Showing 1–50 of 70 results for author: Islam, K

Antisite-disorder driven tuning of magnetic properties and exchange-bias in Nd$_{2-x}$Sr$_{x}$CoMnO$_{6-δ}$ $(0 \leq x \leq 1)$ ($δ\sim 0.5$) double perovskites

Authors: Kazi Parvez Islam, Jayjit Kumar Dey, Sourav Chowdhury, Samyabrata Paria, Flora Banerjee, Suryakanta Mishra, Suman Kalyan Samanta, Moritz Hoesch, Robert Dankelman, Indu Dhiman, Debraj Choudhury

Abstract: We demonstrate precise control of exchange bias (EB) in the Nd$_{2-x}$Sr$_x$CoMnO$_{6-δ}$ ($0 \leq x \leq 1$) double-perovskite series through Sr$^{2+}$ induced hole doping, unveiling a remarkable transition between normal and inverse EB states. Employing neutron powder diffraction and X-ray absorption spectroscopy, we reveal a structural evolution from a B-site-ordered monoclinic ($P2_1/n$) phase… ▽ More We demonstrate precise control of exchange bias (EB) in the Nd$_{2-x}$Sr$_x$CoMnO$_{6-δ}$ ($0 \leq x \leq 1$) double-perovskite series through Sr$^{2+}$ induced hole doping, unveiling a remarkable transition between normal and inverse EB states. Employing neutron powder diffraction and X-ray absorption spectroscopy, we reveal a structural evolution from a B-site-ordered monoclinic ($P2_1/n$) phase to a disordered rhombohedral ($R\overline{3}c$) phase with increasing $x$, accompanied by a shift in the effective Co valence from +2 toward +3, while the Mn valence remains essentially unchanged. DC magnetization measurements indicate a gradual suppression of ferromagnetism with hole doping, whereas AC susceptibility measurements at $x = 0.75$ reveal pronounced cluster-glass behavior and the highest EB field of $\sim 4$ kOe at 8 K under a 6 T cooling field. After correcting for minor-loop effects, we identify robust inverse EB at $x = 0.75$, persisting even under a cooling field of 6 T. We attribute this phenomenon to competing ferromagnetic--antiferromagnetic and ferromagnetic--glassy interfaces, governed by strong magnetic frustration and the magnetocrystalline anisotropy associated with rare-earth 4$f$ electrons. These findings elucidate the pivotal role of doping-induced structural and magnetic competition in tailoring EB behavior in rare-earth double perovskites, providing new insights for the design of advanced magnetic materials. △ Less

Submitted 15 June, 2026; originally announced June 2026.

Comments: 28 pages, 20 figures

Journal ref: Physical Review B 114, 084407 (2026)

Genome-Guided Interpretable Screening of Phase-Stable, Lead-Free Double Perovskite Absorbers for All-Inorganic Semiconductors, Sensors, and Photovoltaics with DFT-Validated Design Rules

Authors: Nafis Ahtasu, Sohanur Rahman Sohan, Md. Mostaq Ahmed Himel, Md. Zahid Hassan, Muhammad Harussani Moklis, Masud Rana Rashel, Hasan Jamil, AKM Kamrul Islam, Mouhaydine Tlemcani

Abstract: The discovery of stable, lead-free halide perovskites for optoelectronic applications is constrained by vast compositional space and limited interpretability of conventional screening approaches. We present a genome-guided, physics-informed framework that decodes thermodynamic stability and optoelectronic behavior through four physically interpretable descriptor families: packing, bonding, polariz… ▽ More The discovery of stable, lead-free halide perovskites for optoelectronic applications is constrained by vast compositional space and limited interpretability of conventional screening approaches. We present a genome-guided, physics-informed framework that decodes thermodynamic stability and optoelectronic behavior through four physically interpretable descriptor families: packing, bonding, polarization, and electronic identity. Trained on 1,221 DFT-calculated A2BB'X6 compounds, machine-learning surrogates achieve robust predictive performance, with a recall-optimized stability classifier (ROC-AUC = 0.92) and an XGBoost regressor for band-gap prediction (R2 = 0.93 on held-out data). Applying a staged inverse-design constraint stack to 13,088 charge-balanced, lead-free compositions reduces the search space to five DFT-validated, phase-stable semiconductors: Rb2SnMnBr6, Cs2CdSnBr6, Cs2CdSnI6, Cs2KGaI6, and Cs2AgAlBr6. These candidates lie on the convex hull (E_hull <= 0 meV/atom), preserve ordered double-perovskite structures, and exhibit strong optical absorption (alpha peak ~1e5 cm^-1). Genotype-phenotype coupling analysis reveals a hierarchical control mechanism: packing genes define structural formability, bonding genes govern near-edge optical transitions and conductivity, and optoelectronic response genes regulate dielectric response and exciton screening (epsilon0 = 4.6-8.2). This work establishes a generalizable paradigm for interpretable inverse design, linking descriptor-level genomics to experimentally relevant optoelectronic phenotypes and providing design rules for discovering stable, lead-free double perovskites for photovoltaics, sensing, and transparent electronic applications. △ Less

Submitted 21 May, 2026; originally announced May 2026.

Superconductivity mediated by nematic fluctuations -- the dispersion of collective modes

Authors: Kazi Ranjibul Islam, Andrey Chubukov

Abstract: We analyze the spectrum of collective modes in a superconductor in which pairing is mediated by long-range nematic fluctuations. Previous experimental and theoretical studies have found that the superconducting gap in such a system is highly anisotropic and, at any finite $T<T_c$, vanishes on four arcs of the Fermi surface, even when the pairing symmetry is $s$ wave ($s^{+-}$ between hole and elec… ▽ More We analyze the spectrum of collective modes in a superconductor in which pairing is mediated by long-range nematic fluctuations. Previous experimental and theoretical studies have found that the superconducting gap in such a system is highly anisotropic and, at any finite $T<T_c$, vanishes on four arcs of the Fermi surface, even when the pairing symmetry is $s$ wave ($s^{+-}$ between hole and electron pockets). We derive the expression for the pair susceptibility $χ(\mathbf{q},Ω)$ at finite momentum $\mathbf{q}$ and frequency $Ω$ deep in the superconducting phase. We analyze the spectral function, $\operatorname{Im}χ(\mathbf{q},Ω)$, and its pole structure in the transverse (phase) and longitudinal (amplitude) channels, and compare the results with those of a conventional $s$-wave superconductor. We find that the analytic structure of the pair susceptibility in both channels is qualitatively distinct from that in a BCS superconductor. This gives rise to a highly unconventional dispersion of phase and amplitude collective modes. △ Less

Submitted 6 May, 2026; originally announced May 2026.

Spatially resolved collective modes in d-wave superconductors

Authors: Kazi Ranjibul Islam, Samuel Awelewa, Andrey V. Chubukov, Maxim Dzero

Abstract: We analyze the dispersion of collective modes in a superconductor with $d-$wave symmetry of the order parameter in the presence of long-range Coulomb interaction. We use diagrammatic technique and quasiclassical theory in Keldysh-Nambu formalism to compute longitudinal and transverse pair susceptibilities and extract from them the dispersion of the longitudinal and transverse collective mode. We s… ▽ More We analyze the dispersion of collective modes in a superconductor with $d-$wave symmetry of the order parameter in the presence of long-range Coulomb interaction. We use diagrammatic technique and quasiclassical theory in Keldysh-Nambu formalism to compute longitudinal and transverse pair susceptibilities and extract from them the dispersion of the longitudinal and transverse collective mode. We show that at T=0, the dispersion of the transverse (plasma) mode is the same as in an s-wave superconductor, but at a finite temperature it is softer and has a much larger decay rate due to the partial screening of the Coulomb potential by nodal quasiparticles. We show that the dispersion of the longitudinal mode depends on the direction of momentum with respect to the positions of the nodes of the d-wave gap, while the decay rate of this mode does not depend on momentum. We discuss experimental implications of our results. △ Less

Submitted 14 January, 2026; originally announced January 2026.

Comments: 47 pages, 7 figures

Journal ref: Phys. Rev. B 113, 144514 (2026)

Toward Unified Interphase Engineering: The Solid-Electrolyte Interphase in Batteries and Supercapacitors

Authors: Mehedi Hasan, Ishtiaq Murshed, Khayrul Islam, A. K. M. Masud

Abstract: The development of next-generation electrochemical energy storage requires devices that combine the high energy density of batteries with the power capability and long cycle life of supercapacitors. However, the interfacial phenomena governing performance in these systems remain poorly unified. The solid-electrolyte interphase (SEI), a nanoscale film formed by electrolyte decomposition, is well st… ▽ More The development of next-generation electrochemical energy storage requires devices that combine the high energy density of batteries with the power capability and long cycle life of supercapacitors. However, the interfacial phenomena governing performance in these systems remain poorly unified. The solid-electrolyte interphase (SEI), a nanoscale film formed by electrolyte decomposition, is well studied in batteries but its counterpart in supercapacitors has received limited systematic investigation despite growing experimental evidence. This review argues that SEI formation is a universal electrochemical process that occurs whenever electrode potentials drive electron transfer into electrolyte orbitals beyond their stability limits, independent of whether charge storage is Faradaic or non-Faradaic. Differences between battery SEIs and supercapacitor interphases arise mainly from operating conditions, not fundamental chemistry. Engineered interphases created through electrolyte additives, protective coatings, or surface functionalization suppress leakage currents, improve capacitance retention, and enable stable high-voltage operation. By identifying shared mechanisms and establishing transferable design rules, this unified framework provides a foundation for predictive interphase engineering that supports long-lived, high-performance energy-storage technologies. △ Less

Submitted 28 November, 2025; originally announced November 2025.

Curvature-Dependent Polarity of Interfacial Energy Flow in Functionalized CNT Polymer Nanocomposites: A Reactive Molecular Dynamics Perspective

Authors: Mehedi Hasan, Khayrul Islam, Michael T. Kio, AKM Masud

Abstract: Carbon nanotube (CNT)-polymer composites are widely engineered using surface coatings and chemical treatments to improve interfacial bonding and load transfer. It has been suggested in the nanocomposite literature that nanotube curvature, in conjunction with surface functionalization such as polydopamine (PDA) coating, could serve as an additional control knob for tuning interfacial bonding and en… ▽ More Carbon nanotube (CNT)-polymer composites are widely engineered using surface coatings and chemical treatments to improve interfacial bonding and load transfer. It has been suggested in the nanocomposite literature that nanotube curvature, in conjunction with surface functionalization such as polydopamine (PDA) coating, could serve as an additional control knob for tuning interfacial bonding and energy dissipation in polymer-CNT systems. While experimental and simulation studies have demonstrated the benefits of PDA functionalization, the fundamental mechanism by which nanotube curvature modulates interfacial energy flow and mechanical polarity remains unresolved. This gap is sharpened by a persistent paradox: identical PDA functionalization strengthens some CNT-polymer systems while weakening others, a curvature-dependent inconsistency that has remained unexplained. Here, we employ reactive molecular dynamics (ReaxFF) simulations to resolve how curvature and PDA functionalization jointly govern interfacial energy evolution in CNT-polyvinyl alcohol (PVA) nanocomposites. Our investigation reveals that curvature and PDA functionalization jointly produce opposite regimes of interfacial energy flow: high-curvature CNTs generate dissipative, frictional interphases, whereas low-curvature CNTs confine energy in rigid, cohesive shells. This polarity inversion originates from a curvature-induced transition in PDA adsorption geometry that transforms the interphase from an energy-releasing to an energy-storing configuration. These results establish curvature as a fundamental design parameter for engineering polymer-nanotube interfaces, offering a predictive route to tune interfacial energy flow, mechanical resilience, and transport properties beyond the limits of conventional chemical functionalization. △ Less

Submitted 23 November, 2025; originally announced November 2025.

Origin of sublattice particle-hole asymmetry in monolayer FeSe superconductors

Authors: Mercè Roig, Kazi Ranjibul Islam, Basu Dev Oli, Huimin Zhang, P. M. R. Brydon, Aline Ramires, Yue Yu, Michael Weinert, Lian Li, Daniel F. Agterberg

Abstract: In iron-based superconductors, the two Fe atoms in the unit cell are typically related by crystal symmetries; therefore, we expect no intra-unit cell variations in the superconducting gap. However, recent experiments have challenged this expectation, reporting intra-unit cell variations in the gap with an unusual particle-hole asymmetry. Here, we examine the origin of this asymmetry between the tw… ▽ More In iron-based superconductors, the two Fe atoms in the unit cell are typically related by crystal symmetries; therefore, we expect no intra-unit cell variations in the superconducting gap. However, recent experiments have challenged this expectation, reporting intra-unit cell variations in the gap with an unusual particle-hole asymmetry. Here, we examine the origin of this asymmetry between the two Fe sublattices in monolayer FeSe grown on SrTiO$_3$. We reveal that, in addition to the substrate-induced broken inversion symmetry, substrate nematic symmetry breaking is key to observing this asymmetry. We further identify two possible mechanisms through which this can occur. The first is through an odd-parity gap function that coexists with an extended $s$-wave function. The second is via a nodeless $d$-wave gap function that develops in the presence of a symmetry-breaking substrate. We argue that the latter mechanism is more physical. To test our theory, we performed scanning tunneling spectroscopy measurements across the nematic domain walls, which exhibit a clear enhancement of the asymmetry between the two Fe sublattices. In addition, we reveal that the observed sublattice particle-hole asymmetry is associated with odd-frequency pairing correlations, providing an experimental realization of this unusual pairing correlation. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Comments: 5 pages

Generic deformation channels for critical Fermi surfaces including the impact of collisions

Authors: Kazi Ranjibul Islam, Aditya Savanur, Ipsita Mandal

Abstract: This paper constitutes a sequel to our theoretical efforts to determine the nature of generic low-energy deformations of the Fermi surface of a quantum-critical metal, which arises at the stable non-Fermi liquid (NFL) fixed point of a quantum phase transition. The emergent critical Fermi surface, arising right at the Ising-nematic quantum critical point (QCP), is a paradigmatic example where an NF… ▽ More This paper constitutes a sequel to our theoretical efforts to determine the nature of generic low-energy deformations of the Fermi surface of a quantum-critical metal, which arises at the stable non-Fermi liquid (NFL) fixed point of a quantum phase transition. The emergent critical Fermi surface, arising right at the Ising-nematic quantum critical point (QCP), is a paradigmatic example where an NFL behaviour is induced by the strong interactions of the fermionic degrees of freedom with those of the bosonic order parameter. It is an artifact of the bosonic modes becoming massless at the QCP, thus undergoing Landau-damping at the level of one-loop self-energy. We resort to the well-tested formalism of the quantum Boltzmann equations (QBEs) for identifying the excitations. While in our earlier works, we have focused on the collisionless regime by neglecting the collision integral and assuming the bosons to be in equilibrium, here we embark on a full analysis. In particular, we take into account the bosonic part of the QBEs as well, which, however, turn out to have no effect on the solutions. Decomposing the master equation into angular-momentum ($\ell$) channels, the emergent modes are of two types: Fermi-surface deformations with discrete spectra and particle-hole excitations forming a continuous band. The long-lived zero-sound mode, which corresponds to $\ell = 0$, is found to be robust against damping effects. Intriguingly, we have an infinite family of discrete modes corresponding to higher-order harmonics of the net deformation. △ Less

Submitted 16 March, 2026; v1 submitted 9 April, 2025; originally announced April 2025.

Comments: follow up paper of arXiv:2108.09480 and arXiv:2304.04720; journal version

Journal ref: Phys. Rev. B 113, 125130 (2026)

Unconventional Superconductivity Mediated by Nematic Fluctuations in a Multi-Orbital System -- Application to doped FeSe

Authors: Kazi Ranjibul Islam, Andrey Chubukov

Abstract: We analyze superconductivity in a multi-orbital fermionic system near the onset of a nematic order, using doped FeSe as an example. We associate nematicity with a spontaneous polarization between $d_{\text{xz}}$ and $d_{\text{yz}}$ orbitals (a Pomeranchuk-type order) and analyze the pairing mediated by soft nematic fluctuations. Such a pairing gives rise to a highly anisotropic gap function whose… ▽ More We analyze superconductivity in a multi-orbital fermionic system near the onset of a nematic order, using doped FeSe as an example. We associate nematicity with a spontaneous polarization between $d_{\text{xz}}$ and $d_{\text{yz}}$ orbitals (a Pomeranchuk-type order) and analyze the pairing mediated by soft nematic fluctuations. Such a pairing gives rise to a highly anisotropic gap function whose structure strongly varies with temperature, and leads to strongly non-BCS behavior in thermodynamics, spectroscopy and transport. We compute the specific heat and its directional variation with a magnetic field, magnetic susceptibility, density of states, tunneling conductance, Raman intensity, superfluid stiffness and penetration depth without and with impurity scattering and for the latter computed also optical conductivity and $T_c$ variation. We find good agreement with the existing data for FeSe$_{1-x}$S$_x$ and FeSe$_{1-x}$Te$_x$ and suggest new experiments. △ Less

Submitted 9 December, 2024; originally announced December 2024.

Unconventional Superconductivity near a Nematic Instability in a Multi-Orbital system

Authors: Kazi Ranjibul Islam, Andrey Chubukov

Abstract: We analyze superconductivity in a multi-orbital fermionic system near the onset of a nematic order, using doped FeSe as an example. We associate the nematic order with spontaneous polarization between $d_{xz}$ and $d_{yz}$ orbitals. We derive the pairing interaction, mediated by soft nematic fluctuations, and show that it is attractive, and that its strength depends on the position on the Fermi su… ▽ More We analyze superconductivity in a multi-orbital fermionic system near the onset of a nematic order, using doped FeSe as an example. We associate the nematic order with spontaneous polarization between $d_{xz}$ and $d_{yz}$ orbitals. We derive the pairing interaction, mediated by soft nematic fluctuations, and show that it is attractive, and that its strength depends on the position on the Fermi surface. As the consequence, right at the nematic quantum-critical point (QCP), superconducting gap opens up at $T_c$ only at special points and extends into finite arcs at $T < T_c$. In between the arcs the Fermi surface remains intact. This gives rise to highly unconventional behavior of the specific heat, with no jump at $T_c$ and an apparent finite offset at $T=0$, when extrapolated from a finite $T$. We argue that this behavior is consistent with the specific heat data for FeSe$_{1-x}$S$_x$ near critical $x$ for the onset of a nematic order. We discuss the behavior of the gap away from a QCP and the pairing symmetry, and apply the results to FeSe$_{1-x}$S$_x$ and FeSe$_{1-x}$Te$_x$, which both show superconducting behavior near the QCP distinct from that in a pure FeSe. △ Less

Submitted 26 October, 2023; originally announced October 2023.

Comments: 25 pages, 16 figures

Structural, elastic, electronic, bonding, thermo-mechanical and optical properties of predicted NbAlB MAB phase in comparison to MoAlB: DFT based ab-initio insights

Authors: Mst. Bina Aktar, F. Parvin, A. K. M. Azharul Islam, S. H. Naqib

Abstract: In this study, we have used density functional theory (DFT) based first-principles investigation of the physical properties of prospective NbAlB compound for the first time. From the analysis of the cohesive energy and enthalpy of formation, it was found that NbAlB is chemically stable. The physical properties of NbAlB have been compared and contrasted with those obtained for MoAlB. Both these MAB… ▽ More In this study, we have used density functional theory (DFT) based first-principles investigation of the physical properties of prospective NbAlB compound for the first time. From the analysis of the cohesive energy and enthalpy of formation, it was found that NbAlB is chemically stable. The physical properties of NbAlB have been compared and contrasted with those obtained for MoAlB. Both these MAB phases are elastically anisotropic, mechanically stable, machinable and brittle materials. Structural and elastic features reflect the layered features. The estimated hardness of NbAlB is 19.0 GPa comparable to that of MoAlB (20.8 GPa) suggesting that predicted NbAlB is a hard compound and is suitable for heavy duty industrial applications. NbAlB is more machinable than MoAlB. Electronic band structure calculations reveal conventional metallic behavior with the electronic density of states at the Fermi level arising mainly due to the Nb 4d orbitals in NbAlB. The electronic density of states at the Fermi level is significantly higher in NbAlB in comparison to MoAlB, indicating that NbAlB is expected to exhibit higher level of electrical conductivity. Electronic dispersion is highly anisotropic for both MoAlB and NbAlB with substantially large electronic effective masses in the out-of-plane directions. The bonding features have been elucidated via the analysis of the band structure and charge density distribution. Both the compounds have mixed covalent, ionic and metallic bonding characteristics. The Fermi surfaces of MoAlB and NbAlB consists of electron and hole like sheets. The Debye temperatures of MoAlB and NbAlB are comparable. The estimated melting temperature of NbAlB is somewhat lower than that of MoAlB. NbAlB shows excellent reflection characteristics suitable to be used as an efficient solar reflector. NbAlB is also expected to absorb ultraviolet radiation very effectively. △ Less

Submitted 21 May, 2023; originally announced May 2023.

Emergent room-temperature ferroelectricity in spark-plasma sintered DyCrO$_3$ and LaCrO$_3$

Authors: Suryakanta Mishra, Keerthana, Krishna Rudrapal, Biswajit Jana, Kazi Parvez Islam, Archna Sagdeo, Ayan Roy Chaudhuri, Venimadhav Adyam, Debraj Choudhury

Abstract: Identification of novel multiferroic materials with high-ordering temperatures remains at the forefront of condensed matter physics research. In this regard, the antiferromagnetic RCrO$_3$ compounds (like GdCrO$_3$) constitute a promising class of multiferroic compounds, which, however, mostly become ferroelectric concomitant with the antiferromagnetic ordering much below room-temperature, arising… ▽ More Identification of novel multiferroic materials with high-ordering temperatures remains at the forefront of condensed matter physics research. In this regard, the antiferromagnetic RCrO$_3$ compounds (like GdCrO$_3$) constitute a promising class of multiferroic compounds, which, however, mostly become ferroelectric concomitant with the antiferromagnetic ordering much below room-temperature, arising from a subtle competition between the ferroelectric off-centering mode and a non-polar antiferrodistortive rotation mode that inhibits ferroelectricity. Recently, room-temperature ferroelectricity of structural origin, arising from off-centering displacements of R and Cr ions, has been identified in spark-plasma sintered GdCrO$_3$ [Suryakanta Mishra et al., Phys. Rev. B 104, L180101 (2021)]. Interestingly, some of the experimentally observed non-ferroelectric RCrO$_3$ compounds have been theoretically predicted to host similar ferroelectric instabilities. Here, we have identified two such non-ferroelectric RCrO3 compounds, one DyCrO$_3$ (which is reported as a quantum paraelectric) and another LaCrO$_3$ (which is paraelectric), and using a modified synthesis protocol involving spark-plasma-sintering (SPS), we have been successful in engineering an intrinsic room-temperature ferroelectricity in the paramagnetic state, driven by noncentrosymmetric structural phase in both SPS sintered DyCrO$_3$ and LaCrO$_3$, in contrast to room-temperature paraelectricity in solid-state synthesized DyCrO$_3$ and LaCrO$_3$. While the ferroelectricity in SPS-prepared DyCrO$_3$ and LaCrO$_3$ is stable at room-temperature, it undergoes an irreversible transition from a ferroelectric (Pna2$_1$) phase to a paraelectric (Pbnm) phase at 440 K. Significantly, SPS-sintered LaCrO$_3$, which undergoes antiferromagnetic ordering at 290 K, emerges as a promising near room-temperature multiferroic material. △ Less

Submitted 24 June, 2023; v1 submitted 19 May, 2023; originally announced May 2023.

Journal ref: Phys. Rev. B 107, 214104 (2023)

Generic deformation channels for critical Fermi surfaces in the collisionless regime

Authors: Kazi Ranjibul Islam, Ipsita Mandal

Abstract: Using a quantum Boltzmann equation framework, we analyse the nature of generic low-energy deformations of a critical Fermi surface, which exists at the non-Fermi liquid fixed point of a system consisting of fermions interacting with massless bosons. The non-Fermi liquid behaviour arises due to the itinerant quasiparticles of the Fermi surface interacting strongly with the massless bosons, which on… ▽ More Using a quantum Boltzmann equation framework, we analyse the nature of generic low-energy deformations of a critical Fermi surface, which exists at the non-Fermi liquid fixed point of a system consisting of fermions interacting with massless bosons. The non-Fermi liquid behaviour arises due to the itinerant quasiparticles of the Fermi surface interacting strongly with the massless bosons, which on the other hand undergo Landau damping as a result of the mutual interactions. Focussing on the collisionless regime, where we neglect the collision integral, we chalk out the possible excitations spanning the entire spectrum of angular momentum ($\ell$) channels (i.e., including both small and large values of $\ell$). The excitations are of two types: particle-hole like localized excitations forming an energy band (or continuum) and delocalized collective modes with discrete energies. Although we find a collective mode analogous to the zero sound of a Fermi liquid, its dispersion shows a crossover from a $Ω\sim |\mathbf q|^{6/5}$ behaviour to the usual $ Ω\sim |\mathbf q|$ dependence, where $Ω$ and $\mathbf q$ represent the frequency and momentum, respectively. We estimate the frequency scale at which this crossover takes place. We also determine the boundary for the particle-hole continuum in the $Ω$--$\mathbf q$ plane, and observe a crossover from $Ω\sim |\mathbf q|^{3/2}$ to $ Ω\sim |\mathbf q|$ behaviour, determined by another crossover frequency scale. △ Less

Submitted 15 July, 2023; v1 submitted 10 April, 2023; originally announced April 2023.

Comments: follow up paper of arXiv:2108.09480; journal version

Journal ref: Annals of Physics 457, 169409 (2023)

The rise of 212 MAX phase borides, Ti$_2$PB$_2$, Zr$_2$PbB$_2$, and Nb$_2$AB$_2$ [A = P, S]: DFT insights into the physical properties for thermo-mechanical applications

Authors: M. A. Ali, M. M. Hossain, M. M. Uddin, A. K. M. A. Islam, S. H. Naqib

Abstract: An interesting class of ternary metallic borides, known as the 212 MAX phase borides, is the recent advancement of the MAX phase family. In this article, results from ab-initio calculations on unexplored Ti$_2$PB$_2$, Zr$_2$PbB$_2$, and Nb$_2$AB$_2$ [A = P, S] are reported wherein Ti$_2$PB$_2$ along with its 211 boride phase Ti$_2$PB are predicted for the first time. The stability was confirmed by… ▽ More An interesting class of ternary metallic borides, known as the 212 MAX phase borides, is the recent advancement of the MAX phase family. In this article, results from ab-initio calculations on unexplored Ti$_2$PB$_2$, Zr$_2$PbB$_2$, and Nb$_2$AB$_2$ [A = P, S] are reported wherein Ti$_2$PB$_2$ along with its 211 boride phase Ti$_2$PB are predicted for the first time. The stability was confirmed by calculating the formation energy, phonon dispersion curve, and elastic stiffness constants. The obtained elastic constants, elastic moduli, and Vickers hardness values of Ti$_2$PB$_2$, Zr$_2$PbB$_2$, and Nb$_2$AB$_2$ [A = P, S] were found to be significantly larger than those of their counterparts 211 borides and carbides, in a trend similar to other 212 borides. The studied compounds are brittle like most of the MAX and MAB phases. The electronic band structure and density of states revealed the metallic nature of the titled borides. Several thermal parameters were explored, certifying the suitability of Ti2PB2, Zr2PbB2, and Nb2AB2 [A = P, S] compared to their counterparts, and a similar trend was found for the other 212 borides. The obtained results predict that Ti2PB2, Zr2PbB2, and Nb2AB2 [A = P, S] have significant potential for use as efficient thermal barrier coating materials. The response of Ti$_2$PB$_2$, Zr$_2$PbB$_2$, and Nb$_2$AB$_2$ [A = P, S] to the incident photon was studied by computing the dielectric constant (real and imaginary part), refractive index, absorption coefficient, photoconductivity, reflectivity, and energy loss function. The ability to protect from solar heating was revealed from the studied reflectivity spectra. In this work, we have explored the physical basis of the improved thermo-mechanical properties of 212 MAX phase borides compared to their carbide and boride counterparts. △ Less

Submitted 2 September, 2022; v1 submitted 17 July, 2022; originally announced July 2022.

Comments: 36 pages

A comprehensive first principles calculations on (Ba0.82K0.18)(Bi0.53Pb0.47)O3 single-cubic-perovskite superconductor

Authors: Mirza H. K. Rubel, Sujon Kumar Mitro, Khandaker Monower Hossain, Md. Mijanur Rahaman, M. Khalid Hossain, Jaker Hossain, B. K. Mondal, Istiak Ahmed, A. K. M. A. Islam, A. El-Denglawey

Abstract: In this present study, the pseudopotential plane-wave (PP-PW) pathway in the scheme of density functional theory (DFT) is utilized to investigate the various physical properties on (Ba0.82K0.18)(Bi0.53Pb0.47)O3 (BKBPO) single perovskite superconductor. We have analyzed elastic constants and moduli at zero and elevated pressures (up to 25 GPa) as well. We also have investigated the anisotropic natu… ▽ More In this present study, the pseudopotential plane-wave (PP-PW) pathway in the scheme of density functional theory (DFT) is utilized to investigate the various physical properties on (Ba0.82K0.18)(Bi0.53Pb0.47)O3 (BKBPO) single perovskite superconductor. We have analyzed elastic constants and moduli at zero and elevated pressures (up to 25 GPa) as well. We also have investigated the anisotropic nature incorporating both the theoretical indices and graphical representations in 2D and 3D dimensions, which reveals a high level of anisotropy. The flatness of the energy bands near EF is a sign of Van-Hf singularity that might increase the electron pairing and origination of high-TC superconductivity. The computed band structure exhibits its metallic characteristics is confirmed by band overlapping. A band of DOS is formed for the strong hybridization of the constituent elements. The orbital electrons of O-2p contribute most dominantly at EF in contrast to all orbital electrons. The orbital electrons at the EF are higher from both the partial density of states and charge density mapping investigation. The coexistence of the electron and hole-like Fermi sheets exhibits the multi-band nature of BKBPO. On the other hand, Fermi surfaces with flat faces promote transport features and Fermi surface nesting as well. The calculated value of the electron-phonon coupling constant (λ = 1.46) is slightly lower than the isostructural superconductor, which indicates that the studied BKBPO can be treated as a strongly coupled superconductor similar to the reported isostructural perovskite superconductors. Furthermore, the thermodynamic properties have been evaluated and analyzed at elevated temperature and pressure by using harmonic Debye approximation (QHDA). △ Less

Submitted 7 December, 2021; originally announced December 2021.

Comments: 20 pages, 7 figures, 6 tables

Journal ref: Materials Today Communications, 33 (2022) 104302

Newly synthesized 3D boron-rich chalcogenides B12X (X = S, Se): Theoretical characterization of physical properties for optoelectronic and mechanical applications

Authors: M. M. Hossain, M. A. Ali, M. M. Uddin, S. H. Naqib, A. K. M. A. Islam

Abstract: Boron rich chalcogenides have been predicted to have excellent properties for optical and mechanical applications in recent times. In this regard, we report the electronic, optical and mechanical properties of recently synthesized boron rich chalcogenide compounds, B12X (X = S and Se) using density functional theory for the first time. The effects of exchange and correlation functional on these pr… ▽ More Boron rich chalcogenides have been predicted to have excellent properties for optical and mechanical applications in recent times. In this regard, we report the electronic, optical and mechanical properties of recently synthesized boron rich chalcogenide compounds, B12X (X = S and Se) using density functional theory for the first time. The effects of exchange and correlation functional on these properties are also investigated. The consistency of the obtained crystal structure with the reported experimental results has been checked in terms of lattice parameters. The considered materials are mechanically stable, brittle and elastically anisotropic. Furthermore, the elastic moduli and hardness parameters are calculated, which show that B12S is likely to be a prominent member of hard materials family compared to B12Se. The origin of different in hardness is explained on the basis of density of states near the Fermi level. Reasonably good values of fracture toughness and machinability index for B12X (X= S and Se) are reported. The melting point, Tm for the B12S and B12Se compounds suggests that both solids are stable, at least up to 4208 and 3577 K, respectively. Indirect band gap of B12S (2.27 eV) and B12Se (1.30 eV) are obtained using the HSE06 functional.The electrons of B12Se compound show lighter average effective mass compared to that of B12S compound, which signifies higher mobility of charge carriers in B12Se. The optical properties are characterized using GGA-PBE and HSE06 method and discussed in detail. These compounds possess bulk optical anisotropy and excellent absorption coefficients in visible light region along with very low static value of reflectivity spectra (range: 7.42-14.0% using both functionals) are noted. Such useful features of the compounds under investigation show promise for applications in optoelectronic and mechanical sectors. △ Less

Submitted 19 August, 2021; originally announced August 2021.

Comments: 34 pages, 13 figures, 6 Tables, This study will be submitted for publication internationally very soon

Specific Heat and the gap structure of a Nematic Superconductor, application to FeSe

Authors: Kazi Ranjibul Islam, Jakob Böker, Ilya M. Eremin, Andrey V. Chubukov

Abstract: We report the results of our in-depth analysis of spectroscopic and thermodynamic properties of a multi-orbital metal, like FeSe, which first develops a nematic order and then undergoes a transition into a superconducting state, which co-exists with nematicity. We analyze the angular dependence of the gap function and specific heat $C_V (T)$ of such nematic superconductor. We specifically address… ▽ More We report the results of our in-depth analysis of spectroscopic and thermodynamic properties of a multi-orbital metal, like FeSe, which first develops a nematic order and then undergoes a transition into a superconducting state, which co-exists with nematicity. We analyze the angular dependence of the gap function and specific heat $C_V (T)$ of such nematic superconductor. We specifically address three issues: (i) angular dependence of the gap in light of the competition between nematicity-induced $s$-$d$ mixture and orbital transmutation of low-energy excitations in the nematic state, (ii) the effect of nematicity on the magnitude of the jump of the specific heat $C_V (T)$ at $T_c$ and the temperature dependence of $C_V (T)$ below $T_c$, and (iii) a potential transition at $T_{c1} < T_c$ from an $s+d$ state to an $s + e^{iη} d$ state that breaks time-reversal symmetry. We consider two scenarios for a nematic order: scenario A, in which this order develops between $d_{xz}$ and $d_{yz}$ orbitals on hole and electron pockets and scenario B, in which there is an additional component of the nematic order for $d_{xy}$ fermions on the two electron pockets. △ Less

Submitted 25 June, 2021; originally announced June 2021.

Comments: 21 pages, 19 figures

Journal ref: Phys. Rev. B 104, 094522 (2021)

Enhanced thermo-mechanical properties of 212 MAX phase borides Zr2AB2 (A = In, Tl): an ab-initio understanding

Authors: M. A. Ali, M. M. Hossain, M. M. Uddin, A. K. M. A. Islam, S. H. Naqib

Abstract: The discovery of MAX phase borides has added a new dimension for research in the materials science community. In this paper, a first-principles study of the newly known MAX phase borides Zr2AB2 (A = In, Tl) has been carried out. The estimated lattice constants and volumes of the unit cell are found to be consistent with previous study. The dynamical and mechanical stability of the titled compounds… ▽ More The discovery of MAX phase borides has added a new dimension for research in the materials science community. In this paper, a first-principles study of the newly known MAX phase borides Zr2AB2 (A = In, Tl) has been carried out. The estimated lattice constants and volumes of the unit cell are found to be consistent with previous study. The dynamical and mechanical stability of the titled compounds have been checked. Fundamental insights into the stiffness constants, elastic moduli, hardness parameters, brittleness and anisotropy indices are presented. The Variation of these mechanical properties was explained based on the Mulliken population analysis and charge density mapping (CDM). The electronic properties have been dealt with by considering electronic band structure and density of states (DOS) which confirmed the metallic nature of Zr2AB2 (A = In, Tl). The lowly dispersive energy bands along the c-direction confirmed anisotropy in conductivity. The analysis of DOS revealed the dominant contribution from Zr-d orbitals to the conductivity with a small contribution from the In/Tl-p states contributing at the Fermi level. The Debye temperature (Theta-D), minimum thermal conductivity (Kmin), Gruneisen parameter and melting temperature (Tm) have been calculated. The higher values of Theta-D and Tm, and lower value of Kmin for Zr2AB2 (A = In, Tl) compared to those of Zr2AC (A = In, Tl). Besides, the specific heat capacities, thermal expansion coefficient, and different thermodynamic potential functions have been calculated. The optical constants have been studied to reveal their possible relevance for application purposes. The reflectivity spectra revealed the applicability of Zr2AB2 (A = In, Tl) as cover materials to diminish the solar heating. The studied physical properties of Zr2AB2 (A = In, Tl) are compared with those of other relevant 212 and 211 MAX phase nanolaminates. △ Less

Submitted 21 March, 2021; originally announced March 2021.

Comments: 33 pages, 9 figures

Journal ref: Journal of Materials Research and Technology (2021)

Origin of high hardness and optoelectronic and thermo-physical properties of boron-rich compounds B6X (X = S, Se): a comprehensive study via DFT approach

Authors: M. M. Hossain, M. A. Ali, M. M. Uddin, A. K. M. A. Islam, S. H. Naqib

Abstract: In the present study, the structural and hitherto uninvestigated mechanical (elastic stiffness constants, machinability index, Cauchy pressure, anisotropy indices, brittleness/ductility, Poissons ratio), electronic, optical, and thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have been explored using density functional theory. The estimated structural lattice parameters were… ▽ More In the present study, the structural and hitherto uninvestigated mechanical (elastic stiffness constants, machinability index, Cauchy pressure, anisotropy indices, brittleness/ductility, Poissons ratio), electronic, optical, and thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have been explored using density functional theory. The estimated structural lattice parameters were consistent with the prior report. The mechanical and dynamical stability of these compounds have been established theoretically. The materials are brittle in nature and elastically anisotropic. The value of fracture toughness, KIC for the B6S and B6Se are ~ 2.07 MPam0.5, evaluating the resistance to limit the crack propagation inside the materials. Both B6S and B6Se compounds possess high hardness values in the range 31-35 GPa, and have the potential to be prominent members of the class of hard compounds. Strong covalent bonding and sharp peak at low energy below the Fermi level confirmed by partial density of states (PDOS) resulted in the high hardness. The profile of band structure, as well as DOS, assesses the indirect semiconducting nature of the titled compounds. The comparatively high value of Debye temperature (ΘD), minimum thermal conductivity (Kmin), lattice thermal conductivity (kph), low thermal expansion coefficient, and low density suggest that both boron-rich chalcogenides might be used as thermal management materials. Large absorption capacities in the mid ultraviolet region (3.2-15 eV) of the studied materials and low reflectivity (~16 %) are significantly noted. Such favorable features give promise to the compounds under investigation to be used in UV surface-disinfection devices as well as medical sterilizer equipment applications. Excellent correlations are found among all the studied physical properties of these compounds. △ Less

Submitted 31 January, 2021; originally announced February 2021.

Comments: 35 pages, 12 figures, 8 Tables (will be submitted for publication in reputed journal)

Mechanical, optoelectronic and thermoelectric properties of half-Heusler p-type semiconductor BaAgP: A DFT investigation

Authors: F. Parvin, M. A. Hossain, M. I. Ahmed, K. Akter, A. K. M. A. Islam

Abstract: We have explored the mechanical, electronic, optical and thermoelectric properties of p-type half-Heusler compound BaAgP for the first time using density functional theory based calculations. The mechanical and dynamical stability of this compound is confirmed by studying the Born stability criteria and phonon dispersion curve, respectively. It is soft, ductile and elastically anisotropic. The ato… ▽ More We have explored the mechanical, electronic, optical and thermoelectric properties of p-type half-Heusler compound BaAgP for the first time using density functional theory based calculations. The mechanical and dynamical stability of this compound is confirmed by studying the Born stability criteria and phonon dispersion curve, respectively. It is soft, ductile and elastically anisotropic. The atomic bonding along a-axis is stronger than that along c-axis. The calculated electronic structure reveals that the studied compound is an indirect band gap semiconductor. The analysis of charge density distribution map and Mulliken population reveals that the bonding in BaAgP is a mixture of covalent and ionic. The optical features confirm that BaAgP is optically anisotropic. The high absorption coefficient and low reflectivity in the visible to ultraviolet region make this compound a possible candidate for solar cell and optoelectronic device applications. The thermoelectric properties have been evaluated by solving the Boltzmann semi-classical transport equations. The calculated power factor at 1000K along a-axis is 35.2 micro-W/cmK2 (with tau=10-14 s) which is ~3.5 times larger than that of SnSe, a promising layered thermoelectric materials. The thermoelectric figure of merit, ZT of BaAgP is 0.44 which is small due to high thermal conductivity. So the reduction of thermal conductivity is essential to enhance thermoelectric performance of BaAgP in device applications. △ Less

Submitted 20 November, 2020; originally announced November 2020.

Comments: 31 pages, 9 figures

DFT insights into new B-containing 212 MAX phases: Hf2AB2 (A = In, Sn)

Authors: M. A. Ali, M. M. Hossain, M. M. Uddin, A. K. M. A. Islam, D. Jana, S. H. Naqib

Abstract: 212 MAX phase borides are new additions to the MAX phase family with enhanced thermo-mechanical properties. In this article, first-principles calculations have been carried out to explore the mechanical properties, Vickers hardness, elastic anisotropy, thermal properties, and optical properties of predicted thermodynamically stable MAX compounds Hf2AB2 (A = In, Sn). The structural properties are c… ▽ More 212 MAX phase borides are new additions to the MAX phase family with enhanced thermo-mechanical properties. In this article, first-principles calculations have been carried out to explore the mechanical properties, Vickers hardness, elastic anisotropy, thermal properties, and optical properties of predicted thermodynamically stable MAX compounds Hf2AB2 (A = In, Sn). The structural properties are compared with the available data to assess the validity of calculations. The mechanical stability of Hf2AB2 (A = In, Sn) compounds is established with the help of the computed stiffness constants (Cij). The possible reason for enhanced mechanical properties and Vickers hardness of Hf2SnB2 is explained based on the analysis of bonding strength, followed by the electronic density of states. Higher mechanical strength and Vickers hardness of Hf2AB2 (A = In, Sn) compared to Hf2AC (A = In, Sn) are also indicated in the light of charge density mapping. The values of Pugh ratio, Poissons ratio and Cauchy pressure predict brittle character of the studied compounds. Besides, the anisotropic nature of the titled borides is investigated by 2D and 3D plots of elastic moduli along with some well established anisotropy indices. Thermal properties were investigated by calculating the Debye temperature, minimum thermal conductivity, Grüneisen parameter, and melting temperature. The thermal properties of Hf2AB2 (A = In, Sn) are also superior to Hf2AC (A = In, Sn). The optical constants such as real and imaginary parts of the dielectric function, refractive index, extinction coefficient, absorption coefficient, photoconductivity, reflectivity, and loss function are investigated. △ Less

Submitted 9 October, 2020; originally announced October 2020.

Comments: 30 pages, 10 figures, 6 tables

Recently predicted ternary boride Hf3PB4: Insights into the physical properties of this hardest possible boride MAX phase

Authors: M. A. Ali, M. M. Hossain, A. K. M. A. Islam, S. H. Naqib

Abstract: In this work, we have explored via first principles study of mechanical properties including Vickers hardness and mechanical anisotropy, electronic charge density distribution, Fermi surface, thermodynamic and optical properties of the recently predicted thermodynamically stable MAX phase boride Hf3PB4 for the first time. The calculated lattice constants of the optimized cell are consistent with t… ▽ More In this work, we have explored via first principles study of mechanical properties including Vickers hardness and mechanical anisotropy, electronic charge density distribution, Fermi surface, thermodynamic and optical properties of the recently predicted thermodynamically stable MAX phase boride Hf3PB4 for the first time. The calculated lattice constants of the optimized cell are consistent with those found by the predicted data available. Mechanical properties such as C44, B, G, Y, Hmacro and Hmicro of Hf3PB4 boride are compared with those of existing MAX phases. None of the MAX compounds synthesized so far has higher Hmacro and/or Hmicro than that of the predicted Hf3PB4 nanolaminate. Calculations of stiffness constants (Cij) indicate that Hf3PB4 is mechanically stable. The extraordinarily high values of elastic moduli and hardness parameters are explained with the use of density of states (DOS) and charge density mapping (CDM). The high stiffness of Hf3PB4 arises because of the additional B atoms which results in the strong B B covalent bonds in the crystal. The band structure and DOS calculations are used to confirm the metallic properties with dominant contribution from the Hf-5d states to the electronic states around the Fermi level. The technologically important thermal parameters such Debye temperature, minimum thermal conductivity, Gruneisen parameter and melting temperature of Hf3PB4 are calculated. It has been found that the estimated melting temperature of Hf3PB4 is also the highest among all the MAX phase nanolaminates. The important optical constants are calculated and analyzed in detail and their relevance to possible applications in the optoelectronic sectors is discussed. Our study reveals that Hf3PB4 has the potential to be the hardest known MAX phase based on the values of C44, Hmacro and Hmicro. △ Less

Submitted 11 September, 2020; originally announced September 2020.

Comments: 37 pages

Physical properties of new MAX phase borides M2SB (M = Zr, Hf and Nb) in comparison with conventional MAX phase carbides M2SC (M = Zr, Hf and Nb): Comprehensive insights

Authors: M. A. Ali, M. M. Hossain, M. M. Uddin, M. A. Hossain, A. K. M. A. Islam, S. H. Naqib

Abstract: In this article, a detailed study of the recently synthesized MAX phase borides M2SB (M = Zr, Hf and Nb) has been performed via first principles technique. Investigation of mechanical hardness, elastic anisotropy, optical properties, dynamical stability and thermal properties are considered for the first time. The estimated values of stiffness constants and elastic moduli are found in good agreeme… ▽ More In this article, a detailed study of the recently synthesized MAX phase borides M2SB (M = Zr, Hf and Nb) has been performed via first principles technique. Investigation of mechanical hardness, elastic anisotropy, optical properties, dynamical stability and thermal properties are considered for the first time. The estimated values of stiffness constants and elastic moduli are found in good agreement with available results. The micro and macro hardness (Hmicro and Hmacro) parameters are calculated. The Vickers hardness is also calculated using Mulliken population analysis. The electronic density of states and charge density mapping are used to explain the variation of stiffness constants, elastic moduli and hardness parameters among the studied ternary borides. The Nb2SB compound is found to show best combination of mechanical properties. Mixture of covalent and ionic bonding within these borides is explained using Mulliken population analysis. The direction dependent values of Youngs modulus, compressibility, shear modulus and Poissons ratio are visualized by 2D and 3D representations and different anisotropic factors are calculated. The important optical constants are calculated and analyzed. The metallic nature of the studied borides is confirmed from the DOS and optical properties. The reflectivity spectra reveal the potential use of Zr2SB as coating materials to diminish solar heating. The studied borides are dynamically stable as confirmed from the phonon dispersion curves. The characteristic thermodynamic properties have also been calculated and analyzed. The physical properties of corresponding 211 MAX phase carbides are also calculated for comparison with those of the titled ternary borides. △ Less

Submitted 9 September, 2020; originally announced September 2020.

Comments: 33 pages, 10 figues, 7 tables

Dynamical stability, Vibrational and optical properties of anti-perovskite A3BX (Ti3TlN, Ni3SnN and Co3AlC) phases: a first principles study

Authors: K. Das, M. A. Ali, M. M. Hossain, S. H. Naqib, A. K. M. A. Islam, M. M. Uddin

Abstract: We have investigated various physical properties including phonon dispersion, thermodynamic parameters, optical constants, Fermi surface, Mulliken bond population, theoretical Vickers hardness and damage tolerance of anti-perovskite A3BX phases for the first time by employing density functional theory (DFT) methodology based on first principles method. Initially we assessed nine A3BX phases in tot… ▽ More We have investigated various physical properties including phonon dispersion, thermodynamic parameters, optical constants, Fermi surface, Mulliken bond population, theoretical Vickers hardness and damage tolerance of anti-perovskite A3BX phases for the first time by employing density functional theory (DFT) methodology based on first principles method. Initially we assessed nine A3BX phases in total and found that only three phases (Ti3TlN, Ni3SnN and Co3AlC) are mechanically and dynamically stable based on analysis of computed elastic constants and phonon dispersion along with phonon density of states. We revisited the structural, elastic and electronic properties of the compounds to judge the reliability of our calculations. Absence of band gap at the Fermi level characterizes the phases under consideration as metallic in nature. The values of Pugh ratio, Poisson ratio and Cauchy factor have predicted the ductile nature associated with strong metallic bonding in these compounds. High temperature feasibility study of the phases has also been performed using the thermodynamic properties, such as the free energy, enthalpy, entropy, heat capacity and Debye temperature. The Vickers hardness of the compounds are estimated to be around 4 GPa which is comparable to many well-known MAX phases, indicating their reasonable hardness and easily machinable nature. The static refractive index n(zero) has been found around 8.0 for the phases under study that appeals as potential candidate to design optoelectronics appliances. The reflectivity is found above 44 percent for the Ti3TlN compound in the energy range of 0 to 14.8 eV demonstrating that this material holds significant promise as a coating agent to avoid solar heating. △ Less

Submitted 9 July, 2020; originally announced July 2020.

Comments: 29 pages

Collective modes of ultracold fermionic alkaline-earth gases with SU(N) symmetry

Authors: Sayan Choudhury, Kazi R. Islam, Yanhua Hou, Jim A. Aman, Thomas C. Killian, Kaden R. A. Hazzard

Abstract: We calculate the collective modes of ultracold trapped alkaline-earth fermionic atoms, which possess an SU($N$) symmetry of the nuclear spin degree of freedom, and a controllable $N$, with $N$ as large as $10$. We calculate the breathing and quadrupole modes of two-dimensional and three-dimensional harmonically trapped gases in the normal phase. We particularly concentrate on two-dimensional gases… ▽ More We calculate the collective modes of ultracold trapped alkaline-earth fermionic atoms, which possess an SU($N$) symmetry of the nuclear spin degree of freedom, and a controllable $N$, with $N$ as large as $10$. We calculate the breathing and quadrupole modes of two-dimensional and three-dimensional harmonically trapped gases in the normal phase. We particularly concentrate on two-dimensional gases, where the shift is more accessible experimentally, and the physics has special features. We present results as a function of temperature, interaction strength, density, and $N$. We include calculations across the collisionless to hydrodynamic crossover. We assume the gas is interacting weakly, such that it can be described by a Boltzmann-Vlasov equation that includes both mean-field terms and the collision integral. We solve this with an approximate scaling ansatz, taking care in two-dimensions to preserve the scaling symmetry of the system. We predict the collective mode frequency shifts and damping, showing that these are measurable in experimentally relevant regimes. We expect these results to furnish powerful tools to characterize interactions and the state of alkaline-earth gases, as well as to lay the foundation for future work, for example on strongly interacting gases and SU($N$) spin modes. △ Less

Submitted 11 May, 2020; v1 submitted 26 January, 2020; originally announced January 2020.

Comments: 11 pages, 4 figures (including appendices)

Journal ref: Phys. Rev. A 101, 053612 (2020)

A comparative theoretical study on physical properties of synthesized AVO3 (A = Ba, Sr, Ca, Pb) perovskites

Authors: Khandaker Monower Hossain, Mirza H. K. Rubel, M. M. Rahaman, M. M. Hossain, Md Imran Hossain, Anjuman Ara Khatun, J. Hossain, A. K. M. A. Islam

Abstract: In this paper, we employ CASTEP based on DFT (density functional theory) calculations to investigate various physical properties of BaVO3, SrVO3, CaVO3 and PbVO3. The elastic constants, bulk modulus, Shear modulus, Young's modulus, Pugh's ratio, Poisson's ratio, Vickers hardness, universal anisotropy index and Peierls stress are calculated to rationalize the mechanical behavior of the aforemention… ▽ More In this paper, we employ CASTEP based on DFT (density functional theory) calculations to investigate various physical properties of BaVO3, SrVO3, CaVO3 and PbVO3. The elastic constants, bulk modulus, Shear modulus, Young's modulus, Pugh's ratio, Poisson's ratio, Vickers hardness, universal anisotropy index and Peierls stress are calculated to rationalize the mechanical behavior of the aforementioned compounds. The study of electronic band structure and density of states (DOS) reveal the strong evidence of metallic behavior for all the perovskites. The analysis of bonding properties exhibits the existence of covalent, ionic and metallic bonds. The optical properties of AVO3 have been carried out and are discussed in this paper as well. The analysis of phonon property implies the dynamical stability of BaVO3 but not for SrVO3, CaVO3 and PbVO3. The values of Debye temperature and minimum thermal conductivity imply that only PbVO3 compound has potential to be used as TBC material. △ Less

Submitted 4 May, 2019; originally announced May 2019.

Comments: 32 pages (double spacing), 10 figures are added

Structural, elastic, thermal and lattice dynamic properties of new 321 MAX phases

Authors: M. A. Hadi, M. A. Rayhan, S. H. Naqib, A. Chroneos, A. K. M. A. Islam

Abstract: A new series of MAX family designated as 321 phases are recently reported with Nb3As2C, V3As2C, Nb3P2C and Ta3P2C. Most of the physical properties of these new MAX phase compounds are unexplored and the present study aims to investigate their structural, elastic, thermal, and lattice dynamical properties. Their mechanical and dynamical stabilities are examined. All the phases are elastically aniso… ▽ More A new series of MAX family designated as 321 phases are recently reported with Nb3As2C, V3As2C, Nb3P2C and Ta3P2C. Most of the physical properties of these new MAX phase compounds are unexplored and the present study aims to investigate their structural, elastic, thermal, and lattice dynamical properties. Their mechanical and dynamical stabilities are examined. All the phases are elastically anisotropic and brittle in nature. The Debye temperatures and lattice thermal conductivities have been calculated. Lattice dynamical features are investigated in detail and infrared and Raman modes are identified. High melting temperature of these compounds are favorable for their applications at elevated temperatures. △ Less

Submitted 6 April, 2019; originally announced April 2019.

Effect of copper content on thermal and mechanical properties of eutectoid zn-al alloy

Authors: A. R. Khan, T. Ahmed, M. K. Islam, S. A. Dhar, M. R. Qadir

Abstract: Zn-Al alloys have become one of the major engineering alloys among commercially available alloys. This study was conducted on eutectoid composition of Zn-Al alloy with an observation of the effect of copper addition. For this purpose, one eutectoid (Zn-22wt%Al) and three other alloys, adding 1wt%, 3wt% and 5wt% copper with this eutectoid composition, were molded in permanent metal mould. Microscop… ▽ More Zn-Al alloys have become one of the major engineering alloys among commercially available alloys. This study was conducted on eutectoid composition of Zn-Al alloy with an observation of the effect of copper addition. For this purpose, one eutectoid (Zn-22wt%Al) and three other alloys, adding 1wt%, 3wt% and 5wt% copper with this eutectoid composition, were molded in permanent metal mould. Microscopic studies exhibited varied grains which confirmed the formation of different phases. Moreover, the formation of different phases in micro study was supported by XRD analysis. Hardness of the samples were tested on Rockwell B scale and it was observed that the hardness of these alloys was substantially increased with the addition of copper. With increasing amount of copper, phase changing temperature of the alloys reveals a growing trend, which was observed by DTA analysis. From this study it was concluded that addition of copper can significantly add to the mechanical properties of Zn-Al alloys. △ Less

Submitted 9 January, 2019; v1 submitted 6 January, 2019; originally announced January 2019.

Comments: 7 Pages Page 267-273 1st International Conference on Engineering Materials and Metallurgical Engineering 22- 24 December, 2016 Bangladesh Council of Scientific and Industrial Research (BCSIR) Dhaka, Bangladesh

Report number: C130

Physical properties of niobium based intermetallics (Nb3B; B = Os, Pt, Au): a DFT based ab-initio study

Authors: M. I. Naher, F. Parvin, A. K. M. A. Islam, S. H. Naqib

Abstract: Structural, elastic and electronic band structure properties of A-15 type Nb-based intermetallic compounds Nb3B (B = Os, Pt, Au) have been revisited using first principles calculations based on the density functional theory (DFT). All these show excellent agreement with previous reports. More importantly, electronic bonding, charge density distribution and Fermi surface features have been studied… ▽ More Structural, elastic and electronic band structure properties of A-15 type Nb-based intermetallic compounds Nb3B (B = Os, Pt, Au) have been revisited using first principles calculations based on the density functional theory (DFT). All these show excellent agreement with previous reports. More importantly, electronic bonding, charge density distribution and Fermi surface features have been studied in detail for the first time. Vickers hardness of these compounds is also studied. The Fermi surfaces of Nb3B contain both hole- and electron-like sheets, the features of which change systematically as one move from Os to Au. The electronic charge density distribution implies that Nb3Os, Nb3Pt and Nb3Au have a mixture of ionic and covalent bondings with a substantial metallic contribution. The charge transfer between the atomic species in these compounds has been explained via the Mulliken bond population analysis and the Hirshfeld population analysis. The bonding properties show a good correspondence to the electronic band structure derived electronic density of states (DOS) near the Fermi level. Debye temperature of Nb3B (B = Os, Pt, Au) have been estimated from the elastic constants and show a systematic behavior as a function of the B atomic species. We have discussed implications of the results obtained in this study in details in this paper. △ Less

Submitted 8 June, 2018; originally announced June 2018.

Comments: Keywords: Intermetallic compounds; Density functional theory; Elastic constants; Electronic band structure; Fermi surface; Bonding characteristics. arXiv admin note: substantial text overlap with arXiv:1706.03314

First principles study of M2InC (M = Zr, Hf and Ta) MAX phases: The effect of M atomic species

Authors: F. Sultana, M. M. Uddin, M. A. Ali, M. M. Hossain, S. H. Naqib, A. K. M. A. Islam

Abstract: We have studied the physical properties of M2InC (M = Zr, Hf and Ta) MAX phases ternary carbides using density functional theory (DFT) methodology. The structural, elastic and electronic properties are revisited (and found to be in good agreement with recently reported results). The charge density distribution, Fermi surface features, Vickers hardness, dynamical stability, thermodynamics and optic… ▽ More We have studied the physical properties of M2InC (M = Zr, Hf and Ta) MAX phases ternary carbides using density functional theory (DFT) methodology. The structural, elastic and electronic properties are revisited (and found to be in good agreement with recently reported results). The charge density distribution, Fermi surface features, Vickers hardness, dynamical stability, thermodynamics and optical properties have been investigated for the first time. The calculated single crystal elastic constants and phonon dispersion curves endorse the mechanical and dynamical stability of all the compounds under study. The calculated single crystal elastic constants Cij and polycrystalline elastic constants are found to increase with increasing atomic number of M species (M = Zr, Hf and Ta). The values of Pugh ratio and Poisson ratio revealed the brittleness of the compounds under study associated with strong directional covalent bond with a mixture of ionic contribution. Overlapping of conduction band and valence band at Fermi level notify the metallic nature of M2InC (M = Zr, Hf and Ta) MAX phases. Low values of Vicker hardness indicate the softness of the materials and easy machinability.. The thermodynamic properties, such as the free energy, enthalpy, entropy, specific heat capacity and Debye temperature are evaluated using the phonon dispersion curves and a good correspondence is found with the M atomic species. Electronically important optical properties, e.g., dielectric functions, refractive index, photoconductivity, absorption coefficient, loss function and reflectivity are calculated and discussed in detail in this study. △ Less

Submitted 22 May, 2018; v1 submitted 20 May, 2018; originally announced May 2018.

Comments: page 24

Effects of transition metals on physical properties of M2BC (M = V, Nb, Mo and Ta): a DFT calculation

Authors: P. Barua, M. M. Hossain, M. A. Ali, M. M. Uddin, S. H. Naqib, A. K. M. A. Islam

Abstract: The electronic band structures along with Fermi surface, anisotropy, Vickers hardness, analysis of Mulliken populations, optical and thermodynamic properties were studied for the first time. The optimized unit cell parameters are compared with available theoretical and experimental results and a reasonable agreement is recorded. The mechanical stability of these compounds is confirmed. All the com… ▽ More The electronic band structures along with Fermi surface, anisotropy, Vickers hardness, analysis of Mulliken populations, optical and thermodynamic properties were studied for the first time. The optimized unit cell parameters are compared with available theoretical and experimental results and a reasonable agreement is recorded. The mechanical stability of these compounds is confirmed. All the compounds herein exhibit metallic conductivity where major contribution comes from d-orbital electrons. The hardness values of 10.71, 12.44, 8.52 and 16.80 GPa were recorded for M2BC (M = V, Nb, Mo and Ta) compounds, respectively. The value of bulk modulus, B is found to increase in the sequence B (V2BC) < B (Nb2BC) < B (Ta2BC) < B (Mo2BC), indicates Mo2BC is highly stiff among all compounds. The Mo2BC and Ta2BC compound might be considered as potential candidates for protection of cutting and forming tools due to the moderately ductile and highly stiff behavior compared to other benchmark hard coating materials such as TiN, TiAlN, Ti0.5Al0.5N and c-BN. Ta2BC compound could also be a promising thermal barrier coating (TBC) material due to the reasonable results of minimum thermal conductivity, Debye temperature and damage tolerance behavior. Various optical functions such as dielectric constants, refractive index, photo-conductivity, absorption, loss function and reflectivity) are calculated and discussed in details. The amount of reflectivity was always more than around 50% with no significant change in the near infrared, visible light and near ultraviolet region (up to ~6 eV), which results a promising coating material to diminish solar heating as well. △ Less

Submitted 24 May, 2018; v1 submitted 9 May, 2018; originally announced May 2018.

Comments: 26 pages, 10 Figures

Journal ref: Journal of Alloys and Compounds; 18 August 2018

Recently synthesized (Zr1-xTix)2AlC (0 - x - 1) solid solutions: Theoretical study of the effects of M mixing on physical properties

Authors: M. A. Ali, M. M. Hossain, M. A. Hossain, M. T. Nasir, M. M. Uddin, M. Z. Hasan, S. H. Naqib, A. K. M. A. Islam

Abstract: The effects of M atomic species mixing on the physical properties of newly synthesized MAX phase (Zr1-xTix)2AlC solid solutions have been studied by means of density functional theory (DFT) calculations. The lattice constants in good accord with the experimental results, are found to decrease with Ti content. The elastic constants, Cij, and the other polycrystalline elastic moduli have been calcul… ▽ More The effects of M atomic species mixing on the physical properties of newly synthesized MAX phase (Zr1-xTix)2AlC solid solutions have been studied by means of density functional theory (DFT) calculations. The lattice constants in good accord with the experimental results, are found to decrease with Ti content. The elastic constants, Cij, and the other polycrystalline elastic moduli have been calculated. The elastic constants satisfy the mechanical stability conditions of these solid solutions. The constants C11, C33 and C44 are found to increase with Ti contents up to x = 0.67, thereafter these decrease slightly. A reverse trend is followed by C12 and C13. The elastic moduli are also found to increase up to x = 0.67, beyond which these moduli go down slightly. Pughs ratio and Poissons ratio both confirm the brittleness of (Zr1-xTix)2AlC. Different anisotropy factors revealed the anisotropic character of these solid solutions. A non-vanishing value of the electronic energy density of states (EDOS) at the Fermi level suggests that (Zr1-xTix)2AlC are metallic in nature. A mixture of covalent, ionic and metallic bonding has been indicated from the electronic structure with dominant covalent bonding due to hybridization of Zr-4d states and C-2p states. The variation of elastic stiffness and elastic parameters with x is seen to be correlated with partial DOS (PDOS) and charge density distribution. The calculated Debye temperature and minimum thermal conductivity are found to increase with Ti contents, while melting temperature is the highest for x = 0.67. The solid solution with x = 0.67 shows improved mechanical and thermal properties compared to that of the two end members Zr2AlC and Ti2AlC. The study of charge transport properties of (Zr1-xTix)2AlC reveals the metallic nature with saturated resistivity. The maximum power factor is obtained at 400 K for (Zr1-xTix)2AlC. △ Less

Submitted 29 October, 2017; v1 submitted 27 September, 2017; originally announced September 2017.

Comments: 16 pages, 7 figures, submitted to Journal of Alloys and Compounds

Structural, elastic, electronic, and bonding properties of intermetallic Nb3Pt and Nb3Os compounds: a DFT study

Authors: M. I. Naher, F. Parvin, A. K. M. A. Islam, S. H. Naqib

Abstract: Theoretical investigation of structural, elastic, electronic and bonding properties of A-15 Nb-based intermetallic compounds Nb3B (B = Pt, Os) have been performed using first principles calculations based on the density functional theory (DFT). Optimized cell parameters are found to be in good agreement with available experimental and theoretical results. The elastic constants at zero pressure and… ▽ More Theoretical investigation of structural, elastic, electronic and bonding properties of A-15 Nb-based intermetallic compounds Nb3B (B = Pt, Os) have been performed using first principles calculations based on the density functional theory (DFT). Optimized cell parameters are found to be in good agreement with available experimental and theoretical results. The elastic constants at zero pressure and temperature are calculated and the anisotropic behaviors of the compounds are studied. Both the compounds are mechanically stable and ductile in nature. Other elastic properties such as Pugh's ratio, Cauchy pressure, machinability index are derived for the first time. Nb3Os is expected to have good lubricating properties compared to Nb3Pt. The electronic band structure and energy density of states (DOS) have been studied with and without spin-orbit coupling (SOC). The band structures of both the compounds are spin symmetric. Electronic band structure and DOS reveal that both the compounds are metallic and the conductivity mainly arise from the Nb 4d states. The Fermi surface features have been studied for the first time. The Fermi surfaces of Nb3B contain both hole- and electron-like sheets which change as one replaces Pt with Os. The electronic charge density distribution shows that Nb3Pt and Nb3Os both have a mixture of ionic and covalent bonding. The charge transfer between atomic species in these compounds has been explained by the Mulliken bond population analysis. △ Less

Submitted 11 June, 2017; originally announced June 2017.

Comments: Submitted to Journal of Alloys and Compounds

Predicted MAX phase Sc2InC: Dynamical stability, vibrational and optical properties

Authors: A. Chowdhury, M. A. Ali, M. M. Hossain, M. M. Uddin, S. H. Naqib, A. K. M. A. Islam

Abstract: First principles pseudopotential calculations have been performed for the first time to investigate the phonon dispersion, thermodynamic and optical properties including charge density, Fermi surface, Mulliken population analysis, theoretical Vickers hardness of predicted MAX phase Sc2InC. We revisited the structural, elastic and electronic properties of the compound which assessed the reliability… ▽ More First principles pseudopotential calculations have been performed for the first time to investigate the phonon dispersion, thermodynamic and optical properties including charge density, Fermi surface, Mulliken population analysis, theoretical Vickers hardness of predicted MAX phase Sc2InC. We revisited the structural, elastic and electronic properties of the compound which assessed the reliability of our calculations. The analysis of the elastic constants and the phonon dispersion along with phonon density of states indicates the mechanical stability and dynamical stability of the MAX phase. The Helmholtz free energy, internal energy, entropy specific heat capacity and Debye temperature have also been calculated from the phonon density of states. Mulliken population analysis indicates the existence of prominent covalency in chemical bonding of Sc2InC. The electronic charge density mapping shows a combination of ionic, covalent and metallic bonding in the compound. The Fermi surface is comprised due to the low dispersive Sc 3d and C 2p states from the [ScC] blocks. The phase is expected to be a soft material and easily mechinable due to its low Vicker hardness value. Furthermore, the analysis of various optical properties (such as dielectric function, refractive index, photoconductivity, absorption coefficients, loss function and reflectivity) suggests that the nanolaminate Sc2InC is a promising candidate for optoelectronic devices in the visible and ultraviolet energy regions and as a coating material to avoid solar heating. △ Less

Submitted 22 May, 2017; originally announced May 2017.

Comments: Submitted for publication, 15 pages, 6 figure

First-principles study of superconducting ScRhP and ScIrP pnictides

Authors: M. T. Nasir, M. A. Hadi, M. A. Rayhan, M. A. Ali, M. M. Hossain, M. Roknuzzaman, S. H. Naqib, A. K. M. A. Islam, M. M. Uddin, K. Ostrikov

Abstract: For the first time, we have reported in this study an ab initio investigation on elastic properties, Debye temperature, Mulliken population, Vickers hardness, and charge density of superconducting ScRhP and ScIrP phosphides. The optimized cell parameters show fair agreement with experimental results. The elastic constants and moduli, Poisson's as well as Pugh's ratio and elastic anisotropy factors… ▽ More For the first time, we have reported in this study an ab initio investigation on elastic properties, Debye temperature, Mulliken population, Vickers hardness, and charge density of superconducting ScRhP and ScIrP phosphides. The optimized cell parameters show fair agreement with experimental results. The elastic constants and moduli, Poisson's as well as Pugh's ratio and elastic anisotropy factors have also been calculated to understand the mechanical behavior of these ternary compounds. Their mechanical stability is confirmed via the calculated elastic constants. The calculated values for Poisson's and Pugh's ratio indicate the ductile nature of these compounds. ScIrP is expected to be elastically more anisotropic than ScRhP. The estimated value of Debye temperature predicts that ScRhP is thermally more conductive than ScIrP and the phonon frequency in ScRhP is higher than that in ScIrP. The hardness of ScRhP is lower due to the presence of anti-bonding Rh-Rh in ScRhP. The investigated electronic structure predict that the metallic conductivity of ScRhP reduces significantly when Rh is replaced with Ir. The main contribution to the total density of states (TDOS) at Fermi-level (EF) comes from the d-electrons of Sc and Rh/Ir in both compounds. These two ternary compounds are characterized mainly by metallic and covalent bonding with little ionic contribution. As far as superconductivity is concerned, the matrix elements of electron-phonon interaction are noticeably enhanced in ScIrP compared to that in ScRhP. △ Less

Submitted 17 May, 2017; originally announced May 2017.

Comments: Slightly modified version of the one submitted to the Computational Materials Science

Mechanical behavior, bonding nature, and defect processes of Mo2ScAlC2: a new ordered MAX phase

Authors: M. A. Hadi, S. H. Naqib, S. -R. G. Christopoulos, A. Chroneos, A. K. M. A. Islam

Abstract: In the present study we employed density functional theory calculations to investigate the mechanical behavior, bonding nature and defect processes of the new ordered MAX phase Mo2ScAlC2. The mechanical stability of the compound is verified with its single crystal elastic constants. The new phase Mo2ScAlC2 is anticipated to be prone to shear along the crystallographic b and c axes, when a rational… ▽ More In the present study we employed density functional theory calculations to investigate the mechanical behavior, bonding nature and defect processes of the new ordered MAX phase Mo2ScAlC2. The mechanical stability of the compound is verified with its single crystal elastic constants. The new phase Mo2ScAlC2 is anticipated to be prone to shear along the crystallographic b and c axes, when a rational force is applied to the crystallographic a axis. The compressibility along the <001> direction under uniaxial stress is expected to be easier in Mo2ScAlC2. Additionally, the volume deformation should be easier in Mo2ScAlC2 than in the isostructural Mo2TiAlC2. Mo2ScAlC2 is predicted to behave in a brittle manner. Due to its higher Debye temperature, Mo2ScAlC2 is expected to be thermally more conductive than Mo2TiAlC2. The cross-slip pinning procedure should be significantly easier in Mo2ScAlC2 as compared to Mo2TiAlC2. The new ordered MAX phase Mo2ScAlC2 has a mixed character of strong covalent and metallic bonding with limited ionic nature. Both Mo-C and Mo-Al bonds are expected to be more covalent in Mo2ScAlC2 than those of Mo2TiAlC2. the level of covalency of Sc-C bond is somewhat low compared to a similar bond Ti-C in Mo2TiAlC2. Due to its reduced hardness, Mo2ScAlC2 should be softer and more easily machinable compared to Mo2TiAlC2. Fermi surface topology of the new compound is formed mainly due to the low-dispersive Mo 4d-like bands. The intrinsic defect processes reveal that the level of radiation tolerance in Mo2ScAlC2 is not as high as in other MAX phases such as Ti3AlC2. △ Less

Submitted 9 February, 2017; originally announced February 2017.

Comments: Submitted to Journal of Alloys and Compounds

Ab-initio study of mechanical and electronic properties of MoAlB

Authors: M. A. Ali, M. A. Hadi, M. M. Hossain, S. H. Naqib, A. K. M. A. Islam

Abstract: Using first-principles calculations, the structural, elastic and electronic properties of MoAlB have been investigated for the first time. The optimized lattice constants exhibit fair agreement with the experimental values. The computed elastic constants satisfy the mechanical stability conditions for the MoAlB. The Mo-based boride MoAlB is elastically anisotropic and can be classified as brittle… ▽ More Using first-principles calculations, the structural, elastic and electronic properties of MoAlB have been investigated for the first time. The optimized lattice constants exhibit fair agreement with the experimental values. The computed elastic constants satisfy the mechanical stability conditions for the MoAlB. The Mo-based boride MoAlB is elastically anisotropic and can be classified as brittle material. This boride is expected to show reasonable thermal conductivity due to its high Debye temperature of 693 K. The metallic electrical conductivity of this compound is predicted from the electronic band structure calculations. The chemical bonding in MoAlB is basically covalent in nature which is supported by the calculated electronic density of states (DOS), Mulliken population, and charge density distribution. The estimated hardness value of 11.6 GPa for MoAlB suggests that it is softer compared to many other borides. The Fermi surface is formed due to low dispersive Mo 4d-like bands, which makes the compound a conductive one. △ Less

Submitted 26 January, 2017; originally announced January 2017.

New Ternary Superconducting Compound LaRu2As2: Physical Properties from DFT Calculations

Authors: M. A. Hadi, M. S. Ali, S. H. Naqib, A. K. M. A. Islam

Abstract: In this paper, we have presented the density functional theory (DFT) based calculations performed within the first-principles pseudopotential method to investigate the physical properties of the newly discovered superconductor LaRu2As2 for the first time. The optimized structural parameters are in good agreement with the experimental results. The calculated independent elastic constants ensure mec… ▽ More In this paper, we have presented the density functional theory (DFT) based calculations performed within the first-principles pseudopotential method to investigate the physical properties of the newly discovered superconductor LaRu2As2 for the first time. The optimized structural parameters are in good agreement with the experimental results. The calculated independent elastic constants ensure mechanical stability of the compound. The calculated Cauchy pressure, Pugh's ratio as well as Poisson's ratio indicate that LaRu2As2 should behave as a ductile material. Due to low Debye temperature, LaRu2As2 may be used as a thermal barrier coating (TBC) material. The new compound should exhibit metallic nature as its valence bands overlap considerably with the conduction bands. LaRu2As2 is expected to be a soft material and easily machineable because of its low hardness value of 6.8 Gpa. The multi-band nature is observed in calculated Fermi surface. A highly anisotropic combination of ionic, covalent, and metallic interactions is expected in accordance with charge density calculations. △ Less

Submitted 12 December, 2016; originally announced December 2016.

Comments: To appear in Chinese Physics B

Noise-induced subdiffusion in strongly localized quantum systems

Authors: Sarang Gopalakrishnan, K. Ranjibul Islam, Michael Knap

Abstract: We consider the dynamics of strongly localized systems subject to dephasing noise with arbitrary correlation time. Although noise inevitably induces delocalization, transport in the noise-induced delocalized phase is subdiffusive in a parametrically large intermediate-time window. We argue for this intermediate-time subdiffusive regime both analytically and using numerical simulations on single-pa… ▽ More We consider the dynamics of strongly localized systems subject to dephasing noise with arbitrary correlation time. Although noise inevitably induces delocalization, transport in the noise-induced delocalized phase is subdiffusive in a parametrically large intermediate-time window. We argue for this intermediate-time subdiffusive regime both analytically and using numerical simulations on single-particle localized systems. Furthermore, we show that normal diffusion is restored in the long-time limit, through processes analogous to variable-range hopping. With numerical simulations based on Lanczos exact diagonalization, we demonstrate that our qualitative conclusions are also valid for interacting systems in the many-body localized phase. △ Less

Submitted 27 July, 2017; v1 submitted 15 September, 2016; originally announced September 2016.

Comments: 5 pages, 4 figures + Supplemental Material, v2: additional data on noise-induced dynamics in many-body localized systems

Journal ref: Phys. Rev. Lett. 119, 046601 (2017)

First-principles prediction of mechanical and bonding characteristics of new T2 superconductor Ta5GeB2

Authors: M. A. Hadi, M. T. Nasir, M. Roknuzzaman, M. A. Rayhan, S. H. Naqib, A. K. M. A. Islam

Abstract: In the present paper, DFT (Density Functional Theory) based first-principles methods are applied to investigate the mechanical and bonding properties of newly synthesized T2 phase superconductor Ta5GeB2 for the first time. The calculated lattice constants are in reasonable agreement with the experiment. The elastic constants (Cij), bulk modulus (B), shear modulus (G), Young's modulus (Y), Poisson… ▽ More In the present paper, DFT (Density Functional Theory) based first-principles methods are applied to investigate the mechanical and bonding properties of newly synthesized T2 phase superconductor Ta5GeB2 for the first time. The calculated lattice constants are in reasonable agreement with the experiment. The elastic constants (Cij), bulk modulus (B), shear modulus (G), Young's modulus (Y), Poisson ratio (nu), Pugh ratio (G/B), and elastic anisotropy factor, A, of Ta5GeB2 are calculated to explore the mechanical behavior of the compound.To give an explanation of the bonding nature of this new ternary tetragonal system, the band structure, density of states, and Mulliken atomic population are investigated. The estimated Debye temperature and Vickers hardness are also used to justify both the mechanical and bonding properties of Ta5GeB2. △ Less

Submitted 21 July, 2016; originally announced July 2016.

Comments: To appear in Physica Status Solidi B (2016)

Newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX phases: A first-principles study

Authors: M. A. Ali, M. M. Hossain, N. Jahan, S. H. Naqib, A. K. M. A. Islam

Abstract: The structural, elastic, and electronic properties of newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX nanolaminates have been studied using first-principles density functional theory (DFT) calculations for the first time. Theoretical Vickers hardness has also been estimated for these compounds. All the calculated results are compared with experimental data and also… ▽ More The structural, elastic, and electronic properties of newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX nanolaminates have been studied using first-principles density functional theory (DFT) calculations for the first time. Theoretical Vickers hardness has also been estimated for these compounds. All the calculated results are compared with experimental data and also with that of recently discovered Zr2AlC phase, where available. Zr2(Al0.58Bi0.42)C and Zr2(Al0.2Sn0.8)C are the two first Bi and Sn containing MAX compounds. The calculated structural parameters are found to be in good agreement with the experimental data. The single crystal elastic constants Cij and other polycrystalline elastic coefficients have been calculated and the mechanical stabilities of these compounds have been theoretically confirmed. The bulk modulus increases and the shear modulus decreases due to partial Bi/Sn/Sb substitution for Al in Zr2AlC. The calculated elastic moduli show that these Bi/Sn/Sb containing MAX phases are more anisotropic than Zr2AlC, and have a tendency towards ductility. The Vickers hardness decreases in the Bi/Sn/Sb containing compounds. Further, the electronic band structures and electronic density of states (EDOS) are calculated and the effects of different elemental substitution on these properties are investigated. The electronic band structures show metallic characteristics with contribution predominantly coming from the Zr 4d orbitals. Partial presence of Bi/Sn/Sb atoms increases the EDOS at the Fermi level to some extent. Possible implications of the theoretical results for these recently discovered MAX nanolaminates have been discussed in detail in this paper. △ Less

Submitted 8 December, 2016; v1 submitted 21 April, 2016; originally announced April 2016.

Comments: Submitted to Computational Materials Science

Journal ref: Computational Materials Science 131 (2017) 139

First Principles Study of SnO Under High Pressure

Authors: Md. Ashraf Ali, A. K. M. Azharul Islam, Nusrat Jahan, Syeda Karimunnesa

Abstract: This article reports the study of SnO by using the first-principles pseudopotential plane-wave method within the generalized gradient approximation (GGA). We have calculated the structural, elastic, electronic and optical of SnO under high pressure. The elastic properties such as the elastic constants Cij bulk modulus, shear modulus, Young modulus, anisotropic factor, Pugh ratio, Poisson ratio are… ▽ More This article reports the study of SnO by using the first-principles pseudopotential plane-wave method within the generalized gradient approximation (GGA). We have calculated the structural, elastic, electronic and optical of SnO under high pressure. The elastic properties such as the elastic constants Cij bulk modulus, shear modulus, Young modulus, anisotropic factor, Pugh ratio, Poisson ratio are calculated and analyzed. Mechanical stability of SnO at all pressure are confirmed by using Born stability criteria in terms of elastic constants and are associated with ductile behaviour based on G/B ratios. It is also found that SnO exhibits very high anisotropy. The energy band structure and density of states are also calculated and analyzed. The results show the semiconducting and metallic properties at 0 (zero) and high pressure, respectively. Furthermore, the optical properties such as dielectric function, refractive index, photoconductivity, absorption coefficients, loss function and reflectivity are also calculated. All the results are compared with those of the SnO where available but most of the results at high pressure are not compared due to unavailability of the results. △ Less

Submitted 21 July, 2016; v1 submitted 26 March, 2016; originally announced March 2016.

Comments: 08 pages

Journal ref: International Journal of Modern Physics B 30 (2016) 1650228

Ab initio Investigation of Vibrational, Thermodynamic, and Optical properties of Sc2AlC MAX compound

Authors: M. A. Ali, M. T. Nasir, M. R. Khatun, A. K. M. A. Islam, S. H. Naqib

Abstract: The structural, vibrational, thermodynamical and optical properties of technologically important, weakly coupled MAX compound, Sc2AlC are calculated using density functional theory (DFT). The structural properties of Sc2AlC are compared with results reported earlier. The vibrational, thermodynamical, and optical properties are theoretically estimated for the first time. The phonon dispersion curve… ▽ More The structural, vibrational, thermodynamical and optical properties of technologically important, weakly coupled MAX compound, Sc2AlC are calculated using density functional theory (DFT). The structural properties of Sc2AlC are compared with results reported earlier. The vibrational, thermodynamical, and optical properties are theoretically estimated for the first time. The phonon dispersion curve has been calculated and the dynamical stability of this compound has been investigated. The optical and acoustic modes are observed clearly. We have calculated the Helmholtz free energy (F), internal energy (E), entropy (S) and specific heat capacity (Cv) from the phonon density of states. Various optical parameters have also been calculated. The reflectance spectrum shows that it this compound has the potential to be used as a solar reflector. △ Less

Submitted 24 March, 2016; originally announced March 2016.

Comments: Submitted for publication

New MAX Phase Compound Mo2TiAlC2: First-principles Study

Authors: M. S. Ali, M. A. Rayhan, M. A. Ali, R. Parvin, A. K. M. A. Islam

Abstract: A theoretical study of Mo2TiAlC2 compound belonging to the MAX phases has been performed by using the firstprinciples pseudopotential plane-wave method within the generalized gradient approximation. We have calculated the structural, elastic, electronic and optical properties of Mo2TiAlC2. To confirm mechanical stability, the elastic constants Cij are calculated. Other elastic parameters such as b… ▽ More A theoretical study of Mo2TiAlC2 compound belonging to the MAX phases has been performed by using the firstprinciples pseudopotential plane-wave method within the generalized gradient approximation. We have calculated the structural, elastic, electronic and optical properties of Mo2TiAlC2. To confirm mechanical stability, the elastic constants Cij are calculated. Other elastic parameters such as bulk modulus, shear modulus, compressibility, Young modulus, anisotropic factor, Pugh ratio, Poisson ratio are also calculated. The energy band structure and density of states are calculated and analyzed. The results show that the electrical conductivity is metallic with a high density of states at the Fermi level in which Mo 4d states dominate. Furthermore, the optical properties such as dielectric function, refractive index, photoconductivity, absorption coefficients, loss function and reflectivity are also calculated. Its reflectance spectrum shows that it has the potential to be used as a promising shielding material to avoid solar heating. △ Less

Submitted 14 March, 2016; originally announced March 2016.

Comments: 9 pages

Journal ref: Journal of Scientific Research 8(2) (2016) 109-117

Structural, elastic, and electronic properties of newly discovered Li2PtSi3 superconductor: Effect of transition metals

Authors: M. A. Alam, M. A. Hadi, M. T. Nasir, M. Roknuzzaman, F. Parvin, M. A. K. Zilani, A. K. M. A. Islam, S. H. Naqib

Abstract: First-principles calculations within the density functional theory (DFT) with GGA-PBE exchange-correlation scheme have been employed to predict the structural, the elastic and the electronic properties of newly discovered lithium silicide superconductor, Li2PtSi3, for the first time. All the theoretical results are compared with those calculated recently for isostructural Li2IrSi3. The present stu… ▽ More First-principles calculations within the density functional theory (DFT) with GGA-PBE exchange-correlation scheme have been employed to predict the structural, the elastic and the electronic properties of newly discovered lithium silicide superconductor, Li2PtSi3, for the first time. All the theoretical results are compared with those calculated recently for isostructural Li2IrSi3. The present study sheds light on the effect of replacement of transition metal element Ir with Pt on different mechanical, electronic, and superconducting properties. The effect of spin-orbit coupling on electronic band structure was found to be insignificant for Li2PtSi3. The difference in superconducting transition temperatures of Li2PtSi3 and Li2IrSi3 arises primarily due to the difference in electronic energy density of states at the Fermi level. Somewhat reduced Debye temperature in Li2PtSi3 plays a minor role. We have discussed the implications of the theoretical results in details in this study. △ Less

Submitted 8 February, 2016; originally announced February 2016.

Comments: Submitted for publication

Physical properties of predicted Ti2CdN versus existing Ti2CdC MAX phase: An ab initio study

Authors: M Roknuzzaman, M A Hadi, M J Abedin, M T Nasir, A K M A Islam, M S Ali, K Ostrikov, S H Naqib

Abstract: Ab intio calculations were done to investigate the structural, elastic, electronic and optical properties of the Cd-containing theoretically predicted MAX phase, Ti2CdN, in comparison with the isostructural and already synthesized phase, Ti2CdC. These calculations reveal that the substitution of C by N affects the lattice parameter c, whereas the lattice parameter a, remains almost unchanged. All… ▽ More Ab intio calculations were done to investigate the structural, elastic, electronic and optical properties of the Cd-containing theoretically predicted MAX phase, Ti2CdN, in comparison with the isostructural and already synthesized phase, Ti2CdC. These calculations reveal that the substitution of C by N affects the lattice parameter c, whereas the lattice parameter a, remains almost unchanged. All the elastic constants and moduli increase when carbon is replaced by nitrogen. The elastic anisotropy in Ti2CdC is higher in comparison with that of Ti2CdN. Both these nanolaminates are brittle in nature. The calculated electronic band structures and density of states suggest that the chemical bonding in these two ternary compounds is a combination of covalent, ionic and metallic in nature. Electrical conductivity of Ti2CdC is found to be higher than that of Ti2CdN. The calculated reflectivity spectra show that both the MAX phases Ti2CdC and Ti2CdN have the potential to be used as coating materials to minimize solar heating. △ Less

Submitted 27 November, 2015; originally announced November 2015.

Comments: To appear in Computational Materials Science

Sulvanite Compounds Cu3TMS4 (TM= V, Nb and Ta): Elastic, Electronic, Optical and Thermal Properties using First-principles Method

Authors: M. A. Ali, N. Jahan, A. K. M. A. Islam

Abstract: We present a systematic first-principles study of the structural, elastic, electronic, optical and thermodynamics properties of the sulvanite compounds Cu3TMS4 (TM = V, Nb and Ta). The structural, elastic and electronic properties are in fact revisited using a different calculation code than that used by other workers and the results are compared. The band gaps are found to be 1.041, 1.667 and 1.8… ▽ More We present a systematic first-principles study of the structural, elastic, electronic, optical and thermodynamics properties of the sulvanite compounds Cu3TMS4 (TM = V, Nb and Ta). The structural, elastic and electronic properties are in fact revisited using a different calculation code than that used by other workers and the results are compared. The band gaps are found to be 1.041, 1.667 and 1.815 eV for Cu3VS4, Cu3NbS4 and Cu3TaS4, respectively which are comparable to other available calculated results. The optical properties such as dielectric function, refractive index, photoconductivity, absorption coefficients, reflectivity and loss function have been calculated for the first time. The calculated results are compared with the limited measured data on energy dependent refractive index and reflectivity coefficient available only for Cu3TaS4. All the materials are dielectric, transparent in the visible range. The values of plasma frequencies are found to be 15.36, 15.58 and 15.64 eV for Cu3VS4, Cu3NbS4 and Cu3TaS4, respectively. Furthermore, following the quasi-harmonic Debye model, the temperature effect on the bulk modulus, heat capacity, and Debye temperature is calculated reflecting the anharmonic phonon effects and these are compared with both experimental and other theoretical data where available. △ Less

Submitted 19 October, 2015; originally announced October 2015.

Comments: 13 pages

Journal ref: Journal of Scientific Research 6 (2014) 407-419

First-principles study of Vickers hardness and thermodynamic properties of Ti3SnC2 polymorphs

Authors: M. A. Rayhan, M. A. Ali, S. H. Naqib, A. K. M. A. Islam

Abstract: We have investigated Vickers hardness and the thermodynamic properties of the recently discovered nanolaminate carbide Ti3SnC2 polymorphs using the first-principles calculations. The chemical bonding shows a combination of covalent, ionic and metallic types. The strong covalent bonding is mainly responsible for high Vickers hardness of Ti3SnC2 polymorphs. Thermodynamic properties are studied using… ▽ More We have investigated Vickers hardness and the thermodynamic properties of the recently discovered nanolaminate carbide Ti3SnC2 polymorphs using the first-principles calculations. The chemical bonding shows a combination of covalent, ionic and metallic types. The strong covalent bonding is mainly responsible for high Vickers hardness of Ti3SnC2 polymorphs. Thermodynamic properties are studied using the quasi-harmonic Debye model. The variation of bulk modulus, thermal expansion co-efficient, specific heats, and Debye temperature with applied pressure (P) and temperature (T) are investigated systematically within the ranges of 0 - 50 GPa and 0 - 1000 K. The calculated results have been compared with available experimental and theoretical data. △ Less

Submitted 14 May, 2015; originally announced May 2015.

Comments: 8 pages

Journal ref: JOURNAL OF SCIENTIFIC RESEARCH 7 (2015) 53-64

Structural, Elastic, and Electronic Properties of Recently Discovered Ternary Silicide Superconductor Li2IrSi3: An ab-initio Study

Authors: M. A. Hadi, M. A. Alam, M. Roknuzzaman, M. T. Nasir, A. K. M. A. Islam, S. H. Naqib

Abstract: The structural, elastic, and electronic properties of the very recently discovered ternary silicide superconductor, Li2IrSi3, have been calculated using ab-initio technique. We have carried out the plane-wave pseudopotential approach within the framework of the first-principles density functional theory (DFT) implemented within the CASTEP code. The calculated structural parameters show a reasonabl… ▽ More The structural, elastic, and electronic properties of the very recently discovered ternary silicide superconductor, Li2IrSi3, have been calculated using ab-initio technique. We have carried out the plane-wave pseudopotential approach within the framework of the first-principles density functional theory (DFT) implemented within the CASTEP code. The calculated structural parameters show a reasonable agreement with the experimental results. Elastic moduli of this interesting material have been calculated for the first time. The electronic band structure and electronic energy density of states indicate the strong covalent Ir-Si and Si-Si bonding which lead to the formation of the rigid structure of Li2IrSi3. Strong covalency give rise to a high Debye temperature in this system. We have discussed the theoretical results in detail in this paper. △ Less

Submitted 11 May, 2015; originally announced May 2015.

Comments: Submitted to Current Applied Physics

Synthesized inverse-perovskites Sc3InX (X = B, C, N): A theoretical investigation

Authors: M. A. Hossain, M. S. Ali, F. Parvin, A. K. M. A. Islam

Abstract: We present first-principles density functional theory (DFT) investigations of mechanical, thermodynamic and optical properties of synthesized inverse-perovskites Sc3InX (X = B, C, N). The elastic constants at zero pressure and temperature are calculated and the anisotropic behavior of the compounds is illustrated. All the three materials are shown to be brittle in nature. The computed Peierls stre… ▽ More We present first-principles density functional theory (DFT) investigations of mechanical, thermodynamic and optical properties of synthesized inverse-perovskites Sc3InX (X = B, C, N). The elastic constants at zero pressure and temperature are calculated and the anisotropic behavior of the compounds is illustrated. All the three materials are shown to be brittle in nature. The computed Peierls stress, approximately 3 to 5 times larger than of a selection of MAX phases, show that dislocation movement may follow but with much reduced occurrences compared to these MAX phases. The Mulliken bonding population and charge density maps show stronger covalency between Sc and X atoms compared with Sc-Sc bond. The Vickers hardness values of Sc3InX are predicted to be between 3.03 and 3.88 GPa. The Fermi surfaces of Sc3InX contain both hole- and electron-like topology which changes as one replaces B with C or N. The bulk modulus, specific heats, thermal expansion coefficient, and Debye temperature are calculated as a function both temperature and pressure using the quasi-harmonic Debye model with phononic effects. The results so obtained are analysed in comparison to the characteristics of other related compounds. Moreover optical functions are calculated and discussed for the first time. The reflectivity is found to be high in the IR-UV regions up to ~ 10.7 eV (Sc3InB, Sc3InC) and 12.3 eV (Sc3InN), thus showing promise as good coating materials. Keywords: Sc3InX, Mechanical properties; Fermi surface; Quasi-harmonic Debye model; Thermodynamic properties; Optical properties △ Less

Submitted 24 November, 2012; v1 submitted 22 October, 2012; originally announced October 2012.

Comments: 14 pages, 8 figures, 2 tables, some text modifications. arXiv admin note: substantial text overlap with arXiv:1208.5567