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Interplay of Rashba and Dresselhaus Spin-Orbit Couplings on the Stability of Topological FFLO Phases in 1D Fermi Gases
Authors:
Hamid Mosadeq,
Mohammad-Hossein Zare,
Reza Asgari
Abstract:
We investigate the stabilization of topological Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases, with a specific emphasis on the intraband FFLO phase, in a one-dimensional (1D) Fermi gas subjected to an external magnetic field. This research highlights the crucial role of the interplay between Rashba spin-orbit coupling (RSOC) and Dresselhaus spin-orbit coupling (DSOC). Employing a Fermi-Hubbard mo…
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We investigate the stabilization of topological Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases, with a specific emphasis on the intraband FFLO phase, in a one-dimensional (1D) Fermi gas subjected to an external magnetic field. This research highlights the crucial role of the interplay between Rashba spin-orbit coupling (RSOC) and Dresselhaus spin-orbit coupling (DSOC). Employing a Fermi-Hubbard model alongside the density matrix renormalization group (DMRG) method, we examine the combined effects of RSOC and DSOC on these exotic superfluid phases, taking into account attractive fermionic interactions. Our principal finding reveals that while RSOC primarily stabilizes conventional zero-momentum pairing, DSOC performs a distinct and crucial role in selectively stabilizing the intraband FFLO phase. This stabilization is achieved by enhancing spin polarization within a single helicity band and suppressing interband coherence, thereby facilitating the formation of finite-momentum FFLO pairs within the same band and resulting in the emergence of a topologically nontrivial superfluid. This targeted control of intraband FFLO pairing paves the way for new strategies in the manipulation of superfluid phases in spin-orbit coupled systems and offers essential insights for experimental realizations in ultracold atomic gases, with implications for topological quantum computing and Majorana fermions.
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Submitted 5 December, 2025;
originally announced December 2025.
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Unveiling Non-Kitaev Interactions and Field-Angle Dependence in Topological Magnon Transport of $α$-RuCl$_3$
Authors:
Hamid Mosadeq,
Mohammad-Hossein Zare
Abstract:
Honeycomb lattice Kitaev magnets exhibit exotic magnetic properties governed by the Kitaev interaction. This study delves into $α$-RuCl$_3$, a prototypical example described by effective Hamiltonians encompassing bond-dependent Kitaev interactions alongside additional terms such as the Heisenberg interaction and symmetric off-diagonal exchange interactions. These non-Kitaev terms significantly inf…
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Honeycomb lattice Kitaev magnets exhibit exotic magnetic properties governed by the Kitaev interaction. This study delves into $α$-RuCl$_3$, a prototypical example described by effective Hamiltonians encompassing bond-dependent Kitaev interactions alongside additional terms such as the Heisenberg interaction and symmetric off-diagonal exchange interactions. These non-Kitaev terms significantly influence $α$-RuCl$_3$'s low-temperature magnetism, impacting both magnetic order and excitations. We employ spin-wave theory to elucidate the topological nature of magnetic excitations within the polarized state of $α$-RuCl$_3$ under an external magnetic field. Our focus lies on transverse magnon conductivities, specially the thermal Hall conductivity and spin Nernst coefficient. The calculations unveil a pronounced dependence of the magnitude and sign structure of the low-temperature transverse thermal conductivities on both the applied magnetic field's orientation and the exchange parameters within the nearest neighbor Heisenberg-Kitaev-Gamma-Gamma$'$ $(JKΓΓ')$ model, which govern the nature and strength of spin interactions. This theoretical framework facilitates critical comparisons with experimental observations, ultimately aiding the identification of an effective Hamiltonian for Kitaev magnets exemplified by $α$-RuCl$_3$.
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Submitted 5 November, 2024;
originally announced November 2024.
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Shape and Size-Dependent Surface Plasmonic Resonances of Liquid Metal Alloy (EGaIn) Nanoparticles
Authors:
Sina Jamalzadegan,
Mohammadreza Zare,
Micah J. Dickens,
Florian Schenk,
Alireza Velayati,
Maksym Yarema,
Michael D. Dickey,
Qingshan Wei
Abstract:
Liquid metals (LM) are emerging plasmonic nanomaterials with transformable surface plasmon resonances (SPR) due to their liquid-like deformability. This study delves into the plasmonic properties of LM nanoparticles, with a focus on EGaIn (eutectic gallium-indium)-based materials. Leveraging Finite-Difference Time-Domain (FDTD) simulations and experimental validations for spherical liquid metal na…
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Liquid metals (LM) are emerging plasmonic nanomaterials with transformable surface plasmon resonances (SPR) due to their liquid-like deformability. This study delves into the plasmonic properties of LM nanoparticles, with a focus on EGaIn (eutectic gallium-indium)-based materials. Leveraging Finite-Difference Time-Domain (FDTD) simulations and experimental validations for spherical liquid metal nanoparticles plasmonic properties, we explored the localized SPR (LSPR) effects of EGaIn nanoparticles with various shapes, including nanospheres, dimers, nanorods, nanodisks, nanoellipses, nanocubes, and nanocuboids, in the broad range of ultraviolet (UV)-visible-near infrared (NIR) spectrum. While EGaIn is conventionally known as a UV-active metal alloy, this study reveals unique LSPR features of EGaIn (e.g., higher order resonances, polar and quadrupolar modes) in the broader visible and NIR wavelength ranges, providing a comprehensive map of LSPR properties for different shapes of EGaIn nanoparticles. These findings offer new insights into the dependence of the optical properties of EGaIn nanoparticles on their geometries for diverse applications, ranging from biosensing, nanoelectronics, to optomechanical systems.
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Submitted 11 June, 2025; v1 submitted 29 October, 2024;
originally announced October 2024.
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Ground state of the staggered Heisenberg-$Γ$ honeycomb model in a magnetic field
Authors:
Mojtaba Ahmadi-Yazdi,
Mohammad-Hossein Zare,
Hamid Mosadeq,
Farhad Fazileh
Abstract:
We study the ground state properties of the $S=\frac{1}{2}$ staggered Heisenberg-$Γ$ honeycomb model under a magnetic field based on analytical and numerical methods. Our calculations show that the conventional zigzag and stripy phases are favored because of the staggered Heisenberg interaction away from the pure $Γ$ limit. In our classical analysis, we find that the field induces a series of comp…
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We study the ground state properties of the $S=\frac{1}{2}$ staggered Heisenberg-$Γ$ honeycomb model under a magnetic field based on analytical and numerical methods. Our calculations show that the conventional zigzag and stripy phases are favored because of the staggered Heisenberg interaction away from the pure $Γ$ limit. In our classical analysis, we find that the field induces a series of competing magnetic phases with relatively large unit cells in the region sandwiched between the two magnetic phases with long-range ordering. In the quantum treatment, these large magnetic unit cells are destabilized by strong quantum fluctuations that result in the stabilization of a gapless quantum spin liquid behavior. In a honeycomb $Γ$ magnet, we disclose an intermediate-field gapless quantum spin liquid phase driven by a tilted field away from the out-of-plane direction only for a narrow region between the low-field zigzag and high-field fully polarized phases.
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Submitted 28 April, 2024; v1 submitted 27 October, 2023;
originally announced October 2023.
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Quasicriticality explains variability of human neural dynamics across life span
Authors:
L. J. Fosque,
A. Alipour,
M. Zare,
R. V. Williams-Garcia,
J. M. Beggs,
G. Ortiz
Abstract:
Ageing impacts the brain's structural and functional organization and over time leads to various disorders, such as Alzheimer's disease and cognitive impairment. The process also impacts sensory function, bringing about a general slowing in various perceptual and cognitive functions. Here, we analyze the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) resting-state magnetoencephalography (M…
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Ageing impacts the brain's structural and functional organization and over time leads to various disorders, such as Alzheimer's disease and cognitive impairment. The process also impacts sensory function, bringing about a general slowing in various perceptual and cognitive functions. Here, we analyze the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) resting-state magnetoencephalography (MEG) dataset -- the largest ageing cohort available -- in light of the quasicriticality framework, a novel organizing principle for brain functionality which relates information processing and scaling properties of brain activity to brain connectivity and stimulus. Examination of the data using this framework reveals interesting correlations with age and gender of test subjects. Using simulated data as verification, our results suggest a link between changes to brain connectivity due to ageing, and increased vulnerability to distraction from irrelevant information. Our findings suggest a platform to develop biomarkers of neurological health.
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Submitted 6 September, 2022;
originally announced September 2022.
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Topological Superconductivity in Sn/Si(111) driven by non-local Coulomb interactions
Authors:
Mehdi Biderang,
Mohammad-Hossein Zare,
Jesko Sirker
Abstract:
Superconductivity was recently observed in boron-doped ($\sqrt{3}\times\sqrt{3}$)Sn/Si(111). The material can be described by an extended Hubbard model on a triangular lattice. Here, we use the random-phase approximation to investigate the charge and spin fluctuations as well as the superconducting properties of the system with respect to filling and the relative strength of the extended versus th…
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Superconductivity was recently observed in boron-doped ($\sqrt{3}\times\sqrt{3}$)Sn/Si(111). The material can be described by an extended Hubbard model on a triangular lattice. Here, we use the random-phase approximation to investigate the charge and spin fluctuations as well as the superconducting properties of the system with respect to filling and the relative strength of the extended versus the on-site Hubbard interactions. Our calculations reveal that near half-filling and weak extended Hubbard interactions, the superconducting ground state exhibits chiral $d$-wave pairing. Far from half-filling and for stronger nearest-neighbor Coulomb interactions, the system shows chiral $p$-wave (hole-doping) and $f$-wave (electron-doping) pairings. The dependence of the pairing symmetry on the extended Hubbard interactions suggests that charge fluctuations play an important role in the formation of Cooper pairs. Finally, the temperature dependence of the Knight shift is calculated for all observed superconducting textures and put forward as an experimental method to examine the symmetry of the superconducting gap function.
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Submitted 15 May, 2022;
originally announced May 2022.
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Proximity-driven ferromagnetism and superconductivity in the triangular Rashba-Hubbard model
Authors:
Mehdi Biderang,
Mohammad-Hossein Zare,
Jesko Sirker
Abstract:
Bilayer Moiré structures are a highly tunable laboratory to investigate the physics of strongly correlated electron systems. Moiré transition metal dichalcogenides at low-energies, in particular, are believed to be described by a single narrow band Hubbard model on a triangular lattice with spin-orbit coupling. Motivated by recent experimental evidence for superconductivity in twisted bilayer mate…
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Bilayer Moiré structures are a highly tunable laboratory to investigate the physics of strongly correlated electron systems. Moiré transition metal dichalcogenides at low-energies, in particular, are believed to be described by a single narrow band Hubbard model on a triangular lattice with spin-orbit coupling. Motivated by recent experimental evidence for superconductivity in twisted bilayer materials, we investigate the possible superconducting pairings in a two-dimensional single band Rashba-Hubbard model. Using a random-phase approximation in the presence of nearest and next-nearest neighbor hopping, we analyze the structure of spin fluctuations and the symmetry of the superconducting gap function. We show that Rashba spin-orbit coupling favors ferromagnetic fluctuations which strengthen triplet superconductivity. If parity is violated due to the absence of spatial inversion symmetry, singlet (d-wave) and triplet (p-wave) channels of superconductivity will be mixed. Moreover, we show that time-reversal symmetry can be spontaneously broken leading to a chiral superconducting state. Finally, we consider quasiparticle interference as a possible experimental technique to observe the superconducting gap symmetry.
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Submitted 17 November, 2021;
originally announced November 2021.
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Spin liquid in twisted homobilayers group-VI gichalcogenides
Authors:
Mohammad-Hossein Zare,
Hamid Mosadeq
Abstract:
Twisted transition metal dichalcogenide (TMD) homobilayers have recently emerged as a powerful platform for studying correlated insulating states. In the strongly correlated limit, we construct an effective spin Hamiltonian on a honeycomb lattice that includes the Heisenberg interaction and nonsymmetric interactions such as a Dzyaloshinskii-Moriya interaction and a Kane-Mele coupling for the Mott-…
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Twisted transition metal dichalcogenide (TMD) homobilayers have recently emerged as a powerful platform for studying correlated insulating states. In the strongly correlated limit, we construct an effective spin Hamiltonian on a honeycomb lattice that includes the Heisenberg interaction and nonsymmetric interactions such as a Dzyaloshinskii-Moriya interaction and a Kane-Mele coupling for the Mott-insulating phase at half-filling. For the twisted TMD homobilayers, the spin-orbit coupling in the Hubbard model, which is expected to induce the antisymmetric exchange couplings in the effective spin Hamiltonian, is a highly tunable and experimentally accessible quantity that can be tuned by an applied electric field. In this study, we investigate classical and quantum phase diagrams of the effective spin Hamiltonian using analytical and numerical methods. We show that the model exhibits a rich classical phase diagram including an antiferromagnetic (AFM) phase, a planar spiral ordered phase with high classical degeneracy, a $z$-AFM phase, a noncoplanar phase, a noncollinear phase, and a 120$^{\circ}$-AFM phase. In the quantum treatment, we calculate low-energy magnon excitation spectrum, ground state energy, and static spin structure factor using linear spin-wave theory and density matrix renormalization group methods to compose the quantum phase diagram of the effective spin Hamiltonian. Beyond the Heisenberg interaction, we find that the existence of these antisymmetric couplings is responsible for the quantum spin liquid, $z$-AFM, noncoplanar, and 120$^{\circ}$ phases. Twisted TMD homobilayers, therefore, offer rich platforms for realizing rich phases of matter such as quantum spin liquid, noncoplanar, and 120$^{\circ}$, resulting from the spin-orbit coupling.
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Submitted 1 October, 2021;
originally announced October 2021.
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Probing divacancy defects in a zigzag graphene nanoribbon through RKKY exchange interaction
Authors:
Moslem Zare,
Reza Asgari
Abstract:
We investigate the effect of vacancy defects on the electronic and magnetic properties of zigzag graphene nanoribbons (zGNRs) by making use of the Green's function formalism in combination with the tight-binding Hamiltonian. The evolution of the indirect exchange coupling, known as Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, including single, double, and multiple 5-8-5 divacancy defects is e…
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We investigate the effect of vacancy defects on the electronic and magnetic properties of zigzag graphene nanoribbons (zGNRs) by making use of the Green's function formalism in combination with the tight-binding Hamiltonian. The evolution of the indirect exchange coupling, known as Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, including single, double, and multiple 5-8-5 divacancy defects is explained. Our numerical calculations show that the changes in the electronic structure and the exchange coupling of zGNRs depend significantly on the location of the divacancy defects with respect to the ribbon edges and on the number of the divacancy defects. In the case both the impurities are located on the edge, the magnitude of the exchange coupling is several orders of magnitude strengthen that result when they are placed on the interior of the nanoribbon. Furthermore, a periodic divacancy causes a dramatic change in the magnetic ground state of the ribbon. In the limit of high vacancy potential, the strength of the RKKY interaction is approximately independent of the Fermi energy.
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Submitted 2 June, 2020;
originally announced June 2020.
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Momentum space imaging of locally noncentrosymmetric superconductors
Authors:
Mehdi Biderang,
Mohammad-Hossein Zare,
Alireza Akbari
Abstract:
The failure of spatial inversion symmetry in noncentrosymmetric materials introduces two different types of spin-independent and spin-dependent electron hopping. The spin-dependent term can be translated into a quasi-spin-orbit coupling and may affect the electronic structure. In the locally noncentrosymmetric crystals, the presence of a sublattice degree of freedom generates a distinction between…
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The failure of spatial inversion symmetry in noncentrosymmetric materials introduces two different types of spin-independent and spin-dependent electron hopping. The spin-dependent term can be translated into a quasi-spin-orbit coupling and may affect the electronic structure. In the locally noncentrosymmetric crystals, the presence of a sublattice degree of freedom generates a distinction between the inter- and intra-sublattice hopping integrals. The spin-dependent part of the former (latter), which is even (odd) under parity, is called symmetric (antisymmetric) quasi-spin-orbit coupling. Here, we show the consequences of such quasi-spin-orbit couplings on the electronic band structure and study their characteristic features via the quasiparticle interference method. We extend our discussions to a realistic class of materials, known as transition metal oxides.
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Submitted 29 April, 2021; v1 submitted 10 October, 2019;
originally announced October 2019.
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RKKY plateau in zero- and one-dimensional triangular Kagome lattice models
Authors:
Moslem Zare
Abstract:
Motivated by the research interests on realizing flat bands and magnetization plateaus in kagome lattices, we study the electronic properties and magnetic interactions in both zero- and one-dimensional triangular Kagome lattice (1D-TKL) models, by using the real-space Greens function approach in tight-binding model. We firstly study the electronic properties of both 0D and 1D-TKL in the presence o…
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Motivated by the research interests on realizing flat bands and magnetization plateaus in kagome lattices, we study the electronic properties and magnetic interactions in both zero- and one-dimensional triangular Kagome lattice (1D-TKL) models, by using the real-space Greens function approach in tight-binding model. We firstly study the electronic properties of both 0D and 1D-TKL in the presence of staggered sublattice potential, then, by analyzing the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction in these lattice structures, the magnetic ground states of both 0D and 1D-TKL in the presence of two magnetic adatoms are evaluated. It is found that the 1D channels of TKL show different electronic and magnetic behaviors due to different values of the hopping integrals and spin-orbit couplings. Two important salient features of these TKLs are the presence of flat bands in their band structure as well as the emergence of the RKKY plateaus versus the Fermi energy. These RKKY plateaus have not been reported before, to the best of our knowledge. The most remarkable observation is the potential and Fermi energy variation of the width and location of the RKKY plateaus in both 0D and 1D TKLs. The spatial configurations of the magnetic impurities can also dramatically change the quality and quantity of the RKKY plateaus. We believe that our results provide significant insights towards designing further experiments to search for the realizing of the flat bands and magnetization plateau phases in spintronics and pseudospin electronics devices based on TKLs.
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Submitted 8 September, 2019;
originally announced September 2019.
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Strain-induced modulation of exchange interaction in monolayer zigzag nanoribbons of B$_2$S
Authors:
Moslem Zare
Abstract:
In this work, the strain modulation of electronic structure and magnetic interaction in monolayer nanoribbons of B$_2$S, a recently realized monolayer system, is investigated. In the first part of our study, we focus on how the electronic structure of monolayer nanoribbons of B$_2$S is modified under uniaxial strains, then employing a tight-binding framework together with the conventional theory o…
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In this work, the strain modulation of electronic structure and magnetic interaction in monolayer nanoribbons of B$_2$S, a recently realized monolayer system, is investigated. In the first part of our study, we focus on how the electronic structure of monolayer nanoribbons of B$_2$S is modified under uniaxial strains, then employing a tight-binding framework together with the conventional theory of elasticity, we discuss how strain-induced local deformations can be used as a means to affect Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in zigzag nanoribbons of B$_2$S. We show that breaking inversion symmetry in zigzag B$_2$S nanoribbons (ZBSNR), e.g., by introducing staggered sublattice potentials, play a key role in the modulation of their electronic properties. More interestingly, for the ZBSNRs belong to the group $M=4p$, with $M$ the width of the ZBSNR and $p$ an integer number, one can see that a band gap, in which a pair of near-midgap bands completely detached from the bulk bands is always observed. As a key feature, the position of the midgap bands in the energy diagram of ZBSNRs can be shifted by applying the in-plane strains $\varepsilon_x$ and $\varepsilon_y$. Moreover, the near-midgap bandwidth monotonically decreases with increasing strength of the strain and increases with the width of the ZBSNR. The energy gap of the ZBSNRs decreased with increasing the applied strain and ribbon width. The spatial and strain dependency of the exchange interaction in various configurations of the magnetic impurities are also evaluated. The magnetic interactions between adsorbed magnetic impurities in B$_2$S nanoribbons can be manipulated by careful strain engineering of such systems. Our results suggest that these tunable electronic and magnetic properties of ZBSNRs mean they may find applications in spintronics and pseudospin electronics based on monolayer B$_2$S nanoribbons.
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Submitted 25 June, 2019;
originally announced June 2019.
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Tuning the electronic structure and magnetic coupling in armchair B$_2$S nanoribbons using strain and staggered sublattice potential
Authors:
Moslem Zare
Abstract:
Monolayer B$_2$S has been recently unveiled as a desirable honeycomb monolayer with an anisotropic Dirac cone. We investigate the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction, between two magnetic impurity moments in armchair-terminated B$_2$S nanoribbons in the presence of strain and staggered sublattice potential. By using an accurate tight-binding model, we firstly study the electronic pro…
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Monolayer B$_2$S has been recently unveiled as a desirable honeycomb monolayer with an anisotropic Dirac cone. We investigate the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction, between two magnetic impurity moments in armchair-terminated B$_2$S nanoribbons in the presence of strain and staggered sublattice potential. By using an accurate tight-binding model, we firstly study the electronic properties of all infinite-length armchair B$_2$S nanoribbons (ABSNRs), with different edges, in the presence of both strain and staggered potential. The ABSNRs show different electronic and magnetic behaviors due to different edge morphologies. The band gap energy of ABSNRs depends strongly upon the applied staggered potential and thus one can engineer the electronic properties of the ABSNRs via tuning the external staggered potential. A complete and fully reversible semiconductor (or insulator) to metal transition has been observed via tuning the external staggered potential, which can be easily realized experimentally. A prominent feature is the presence of a quasiflat edge mode, isolated from the bulk modes in the ABSNRs belong to the family $M=6p$, with $M$ the width of the ABSNR and $p$ an integer number. The position of the quasi-flatbands(QFBs) in the energy diagram of ABSNRs can be shifted by applying the in-plane strains. At a critical staggered potential, for nanoribbons of arbitrary width, the QFB changes to a perfect flatband. The RKKY interaction has an oscillating behaviour in terms of the applied staggered potentials and width of the ribbon, such that for two magnetic adatoms randomly distributed on the surface of an ABSNR the staggered potential can reverse the RKKY from antiferromagnetism to ferromagnetism and vice versa. Our findings pave the way for applications in spintronics and pseudospin electronics devices based on ABSNRs.
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Submitted 25 June, 2019;
originally announced June 2019.
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Superconductivity of mixed parity and frequency in an anisotropic spin-orbit coupling
Authors:
Mehdi Biderang,
Mohammad-Hossein Zare,
Alireza Akbari
Abstract:
We illuminate the superconducting phases in [001]-grown-noncentrosymmetric quantum wells with an anisotropic spin-orbit coupling in the presence of on-site Hubbard interaction. Within the random phase approximation, we investigate the spin-fluctuation-mediated pairing in the presence of Rashba/Dresselhaus antisymmetric spin-orbit couplings. Although the existence of spatial inversion symmetry desi…
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We illuminate the superconducting phases in [001]-grown-noncentrosymmetric quantum wells with an anisotropic spin-orbit coupling in the presence of on-site Hubbard interaction. Within the random phase approximation, we investigate the spin-fluctuation-mediated pairing in the presence of Rashba/Dresselhaus antisymmetric spin-orbit couplings. Although the existence of spatial inversion symmetry desires a dominant d-wave pairing for all filling levels, a broken inversion symmetry generates antisymmetric spin-orbit coupling and mixes the even- and odd-parity in the superconducting gap. We study the symmetry of the mixed-parity gap for various strengths of Hubbard interaction. Besides, we consider a superconductor-ferromagnet junction to survey the modifications of superconducting order parameters and observe an admixture of even- and odd-frequencies due to the ferromagnet exchange field.
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Submitted 19 June, 2019;
originally announced June 2019.
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Spike-Phase Coupling As an Order Parameter in a Leaky Integrate-and-Fire Model
Authors:
Nahid Safari,
Farhad Shahbazi,
Mohammad Dehghani-Habibabadi,
Moein Esghaei,
Marzieh Zare
Abstract:
While criticality is widely observed in neural networks, its underlying neural mechanism is not known well. We consider a network of $N$ excitatory leaky integrated and fire (LIF) neurons that reside on a regular lattice with periodic boundary conditions. The cooperation between neurons, $K$, plays the role of the control parameter that is expected to generate criticality when the critical coopera…
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While criticality is widely observed in neural networks, its underlying neural mechanism is not known well. We consider a network of $N$ excitatory leaky integrated and fire (LIF) neurons that reside on a regular lattice with periodic boundary conditions. The cooperation between neurons, $K$, plays the role of the control parameter that is expected to generate criticality when the critical cooperation strength, $K_c$, is adopted. We show that the coupling between spike timing and the phase of temporal fluctuations of a cooperative activity of the network, i.e. population-averaged voltage (PAV), resorts to identifying an order parameter. By increasing $K$, we find a continuous transition from irregular spiking to a phase-locked state at the critical point, $K_c$. Moreover, we deploy the finite-size scaling analysis to obtain the critical exponents of this transition. We also show that the neuronal avalanches created at this critical point, display a remarkable scaling behavior with the exponents in a fair agreement with the experimental values.
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Submitted 27 September, 2019; v1 submitted 3 March, 2019;
originally announced March 2019.
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Tilt-induced anomalous thermal transport in normal/superconducting borophane junctions
Authors:
Moslem Zare
Abstract:
We study charge and heat transport in normal-metal/superconductor (NS) hybrid junction, based on a tilted anisotropic Dirac material. Using the extended Blonder-Tinkham-Klapwijk formalism, the conductance spectra of NS borophane, a two-dimensional Dirac semimetal with two tilted anisotropic Dirac cones in its dispersion, is investigated. Completely different from the usual normal-metal-superconduc…
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We study charge and heat transport in normal-metal/superconductor (NS) hybrid junction, based on a tilted anisotropic Dirac material. Using the extended Blonder-Tinkham-Klapwijk formalism, the conductance spectra of NS borophane, a two-dimensional Dirac semimetal with two tilted anisotropic Dirac cones in its dispersion, is investigated. Completely different from the usual normal-metal-superconductor junctions, in spite of the large mismatch in Fermi wavevectores of the normal-metal and superconductor sides of the borophane NS junction, the electron-hole conversion happens with unit probability at normal incidences. Furthermore, we demonstrate that in the heavily doped superconducting regime for heavily doped normal borophane, the electron-hole conversion happens with unit probability, approximately at any incident angle. The dependence of the Andreev with Fermi energy and bias voltage, enable us, selecting the retroconfiguration or specular configuration in types of Andreev reflection processes. We numerically establish an anomalous behavior of thermal conductance in borophane. The tilting of the Dirac cones gives rise to an anomalous behaviour in the thermal conductance of the NS hybrid junction of borophane, such that the thermal conductance decreases by increasing the temperature. Our findings will have potential applications for transport and energy control in superconducting quantum interference devices and hybridized mesoscopic systems.
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Submitted 9 April, 2019; v1 submitted 30 January, 2019;
originally announced January 2019.
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Thermoelectric transport properties of borophane
Authors:
Moslem Zare
Abstract:
We theoretically study the influence of impurity scattering on the electric and thermal transport of borophane layer, a two-dimensional anisotropic Dirac semi-metal with two tilted and anisotropic Dirac cones. In a systematic framework, we have calculated exactly the electrical conductivity and thermoelectric coefficients of borophane in the presence of the short-range, long-range charged impurity…
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We theoretically study the influence of impurity scattering on the electric and thermal transport of borophane layer, a two-dimensional anisotropic Dirac semi-metal with two tilted and anisotropic Dirac cones. In a systematic framework, we have calculated exactly the electrical conductivity and thermoelectric coefficients of borophane in the presence of the short-range, long-range charged impurity and the short-range electro-magnetic (SREM) scatterers, by using the exact solution of the Boltzmann transport equation within the linear-response theory. Contrary to the large electron-hole asymmetry in borophane, its electron-hole conductivity is nearly symmetric. Interestingly, for the short-range scatters, just like graphene, the short-range conductivities of borophane have the constant values, independent of the chemical potential, while the conductivities of the SREM scatterers are linearly dependent on the chemical potential. Regardless of the impurity type, the electric conductivity of borophane is highly anisotropic, while the Seebeck coefficient and figure of merit (${\it ZT}$) are isotropic. Along with the ambipolar nature of the borophane thermopower, a very high value of ${\it ZT}$ around unity is obtained at room temperature, due to the large asymmetry between electrons and holes in borophane. More importantly, borophane attains its maximum value of ${\it ZT}$ at very low chemical potentials, in the vicinity of the charge neutrality point. In comparison to phosphorene, a highly unique anisotropic 2D material, borophane with a higher anisotropy ratio ($σ_{xx}/σ_{yy}\sim10$), is an unprecedented anisotropic material. This high anisotropy ratio together with the large figure of merit, suggest that borophane is promising for the thermoelectric applications and transport switching in the Dirac transport channels.
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Submitted 15 April, 2019; v1 submitted 24 November, 2018;
originally announced November 2018.
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Resonance spin transfer torque in ferromagnetic/normal/ferromagnetic spin-valve structure of topological insulators
Authors:
Moslem Zare
Abstract:
We theoretically study the spin current and spin-transfer torque generation in a conventional spin- valve hybrid structure of type ferromagnetic/normal metal/ferromagnetic (FM/NM/FM) made of the topological insulator (TI), in which a gate voltage is attached to the normal layer. We demonstrate the penetration of the spin-transfer torque into the right ferromagnetic layer and show that, unlike grap…
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We theoretically study the spin current and spin-transfer torque generation in a conventional spin- valve hybrid structure of type ferromagnetic/normal metal/ferromagnetic (FM/NM/FM) made of the topological insulator (TI), in which a gate voltage is attached to the normal layer. We demonstrate the penetration of the spin-transfer torque into the right ferromagnetic layer and show that, unlike graphene spin-valve junction, the spin-transfer torque in TI is very sensitive to the chemical potential of the NM region. As an important result, by changing the chemical potential of the NM spacer and magnetization directions, one can control all components of the STT. Interestingly, both the resonance spin current and the resonance spin-transfer torque appear for energies determined from a resonance equation. By increasing the chemical potential of the NM spacer, the amplitude of the STTs decreases while at large chemical potentials of $μ_N$ there are intervals of chemical potential in which both the spin current and the spin-transfer torque become zero. These findings could open new perspectives for applications in spin-transfer torque magnetic random access memory (STT-MRAM) devices based on TI.
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Submitted 25 August, 2018;
originally announced August 2018.
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Exchange interaction of magnetic impurities in biased bilayer phosphorene nanoribbon
Authors:
Moslem Zare,
Ebrahim Sadeghi
Abstract:
We study exchange interaction in zigzag bilayer phosphorene nanoribbons (ZBLPNRs) under a perpendicular electric field. We evaluate the spatial and electric field dependency of static spin susceptibility in real space in various configurations of magnetic impurities at zero temperature. The electronic properties of ZBLPNR in the presence of a gate voltage is also obtained. In comparison to the oth…
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We study exchange interaction in zigzag bilayer phosphorene nanoribbons (ZBLPNRs) under a perpendicular electric field. We evaluate the spatial and electric field dependency of static spin susceptibility in real space in various configurations of magnetic impurities at zero temperature. The electronic properties of ZBLPNR in the presence of a gate voltage is also obtained. In comparison to the other two-dimensional (2D) materials such as graphene and silicene, ZBLPNR has two nearly degenerated quasiflat edge modes at the Fermi level, isolated from the bulk states. The band gap modulation of ZBLPNRs by the ribbon width and perpendicular electric field is investigated. Due to the existence of these quasiflat bands at the Fermi level, in the absence of the electric field, a sharp peak in the RKKY interaction is seen. As shown, the signatures of these quasiflat edge modes in ZBLPNRs could be explored by using the RKKY interaction. In the presence of a large bias potential, a beating pattern of the RKKY oscillations occurs when two impurities located inside the ZBLPNR. The electrically tunable RKKY coupling of ZBLPNRs is expected to have important consequences on the spintronic application of biased ZBLPNR.
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Submitted 8 August, 2018;
originally announced August 2018.
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Proximity-Induced Mixed Odd and Even Frequency Pairings in Monolayer NbSe$_2$
Authors:
Mojtaba Rahimi Aliabad,
Mohammad-Hossein Zare
Abstract:
Monolayer superconducting transition metal dichalcogenide NbSe$_2$ is a candidate for a nodal topological superconductor by magnetic field. Because of the so-called Ising spin-orbit coupling that strongly pins the electron spins to the out-of-plane direction, Cooper pairs in monolayer superconductor NbSe$_2$ are protected against an applied in-plane magnetic field much larger than the Pauli limit.…
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Monolayer superconducting transition metal dichalcogenide NbSe$_2$ is a candidate for a nodal topological superconductor by magnetic field. Because of the so-called Ising spin-orbit coupling that strongly pins the electron spins to the out-of-plane direction, Cooper pairs in monolayer superconductor NbSe$_2$ are protected against an applied in-plane magnetic field much larger than the Pauli limit. In monolayer NbSe$_2$, in addition to the Fermi pockets at the corners of Brillouin zone with opposite crystal momentum similar to other semiconducting transition metal dichalcogenides, there is an extra Fermi pocket around the $Γ$ point with much smaller spin splitting, which could lead to an alternative strategy for pairing possibilities that are manipulable by a smaller magnetic field. By considering a monolayer NbSe$_2$-ferromagnet substrate junction, we explore the modified pairing correlations on the pocket at $Γ$ point in hole-doped monolayer NbSe$_2$. The underlying physics is fascinating as there is a delicate interplay of the induced exchange field and the Ising spin-orbit coupling. We realize a mixed singlet-triplet superconductivity, s+f, due to the Ising spin-orbit coupling. Moreover, our results reveal the admixture state including both odd- and even-frequency components, associated with the ferromagnetic proximity effect. Different frequency symmetries of the induced pairing correlations can be realized by manipulating the magnitude and direction of the induced magnetization.
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Submitted 23 July, 2018;
originally announced July 2018.
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Edge currents as a probe of the strongly spin-polarized topological noncentrosymmetric superconductors
Authors:
Mehdi Biderang,
Heshmatollah Yavari,
Mohammad-Hossein Zare,
Peter Thalmeier,
Alireza Akbari
Abstract:
Recently the influence of antisymmetric spin-orbit coupling has been studied in novel topological superconductors such as half-Heuslers and artificial hetero-structures. We investigate the effect of Rashba and/or Dresselhaus spin-orbit couplings on the band structure and topological properties of a two-dimensional noncentrosymetric superconductor. For this goal, the topological helical edge modes…
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Recently the influence of antisymmetric spin-orbit coupling has been studied in novel topological superconductors such as half-Heuslers and artificial hetero-structures. We investigate the effect of Rashba and/or Dresselhaus spin-orbit couplings on the band structure and topological properties of a two-dimensional noncentrosymetric superconductor. For this goal, the topological helical edge modes are analyzed for different spin-orbit couplings as well as for several superconducting pairing symmetries. To explore the transport properties, we examine the response of the spin-polarized edge states to an exchange field in a superconductor-ferromagnet heterostructure. The broken chiral symmetry causes the uni-directional currents at opposite edges.
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Submitted 7 March, 2018;
originally announced March 2018.
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Strongly anisotropic RKKY interaction in monolayer black phosphorus
Authors:
Moslem Zare,
Fariborz Parhizgar,
Reza Asgari
Abstract:
We theoretically study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in two-dimensional black phosphorus, phosphorene. The RKKY interaction enhances significantly for the low levels of hole doping owing to the nearly valence flat band. Remarkably, for the hole-doped phosphorene, the highest RKKY interaction occurs when two impurities are located along the zigzag direction and it tends to a…
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We theoretically study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in two-dimensional black phosphorus, phosphorene. The RKKY interaction enhances significantly for the low levels of hole doping owing to the nearly valence flat band. Remarkably, for the hole-doped phosphorene, the highest RKKY interaction occurs when two impurities are located along the zigzag direction and it tends to a minimum value with changing the direction from the zigzag to the armchair direction. We show that the interaction is highly anisotropic and the magnetic ground-state of two magnetic adatoms can be tuned by changing the rotational configuration of impurities. Owing to the anisotropic band dispersion, the oscillatory behavior with respect to the angle of the rotation is well-described by $\sin(2k_{\rm F}R)$, where the Fermi wavelength $k_{\rm F}$ changes in different directions. We also find that the tail of the RKKY oscillations falls off as $1/R^2$ at large distances.
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Submitted 24 December, 2017;
originally announced December 2017.
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Mixed-pairing superconductivity in 5d Mott insulators with antisymmetric exchange
Authors:
Mohammad-Hossein Zare,
Mehdi Biderang,
Alireza Akbari
Abstract:
We investigate the potential existence of a superconducting phase in $5d$ Mott insulators with an eye to hole doped Sr$_2$IrO$_4$. Using a mean-field method, a mixed singlet-triplet superconductivity, $d + p$, is observed due to the antisymmetric exchange originating from a quasi-spin-orbit-coupling. Our calculation on ribbon geometry shows possible existence of the topologically protected edge st…
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We investigate the potential existence of a superconducting phase in $5d$ Mott insulators with an eye to hole doped Sr$_2$IrO$_4$. Using a mean-field method, a mixed singlet-triplet superconductivity, $d + p$, is observed due to the antisymmetric exchange originating from a quasi-spin-orbit-coupling. Our calculation on ribbon geometry shows possible existence of the topologically protected edge states, because of nodal structure of the superconducting gap. These edge modes are spin polarized and emerge as zero-energy flat bands, supporting a symmetry protected Majorana states, verified by evaluation of winding number and $\mathbb{Z}_2$ topological invariant. At the end, a possible experimental approach for observation of these edge states and determination of the superconducting gap symmetry are discussed based on the quasi-particle interference (QPI) technique.
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Submitted 15 May, 2017;
originally announced May 2017.
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Giant magnetoresistance and anomalous transport in phosphorene-based multilayers with noncollinear magnetization
Authors:
Moslem Zare,
Leyla Majidi,
Reza Asgari
Abstract:
We theoretically investigate the unusual features of the magnetotransport in a monolayer phosphorene ferromagnetic/normal/ferromagnetic (F/N/F) hybrid structure. We find that the charge conductance can feature a minimum at parallel (P) configuration and a maximum near the antiparallel (AP) configuration of magnetization in the F/N/F structure with $n$-doped F and $p$-doped N regions and also a fin…
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We theoretically investigate the unusual features of the magnetotransport in a monolayer phosphorene ferromagnetic/normal/ferromagnetic (F/N/F) hybrid structure. We find that the charge conductance can feature a minimum at parallel (P) configuration and a maximum near the antiparallel (AP) configuration of magnetization in the F/N/F structure with $n$-doped F and $p$-doped N regions and also a finite conductance in the AP configuration with the N region of $n$-type doping. In particular, the proposed structure exhibits giant magnetoresistance, which can be tuned to unity. This perfect switching is found to show strong robustness with respect to increasing the contact length and tuning the chemical potential of the N region with a gate voltage. We also explore the oscillatory behavior of the charge conductance or magnetoresistance in terms of the size of the N region. We further demonstrate the penetration of the spin-transfer torque into the right F region and show that, unlike graphene structure, the spin-transfer torque is very sensitive to the chemical potential of the N region as well as the exchange field of the F region.
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Submitted 25 March, 2017; v1 submitted 14 January, 2017;
originally announced January 2017.
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Thermoelectric transport in monolayer phosphorene
Authors:
Moslem Zare,
Babak Zare Rameshti,
Farnood G. Ghamsari,
Reza Asgari
Abstract:
We apply the generalized Boltzmann theory to describe thermoelectric transport properties of monolayer phosphorene in the presence of short- and long-range charged impurity interactions. First, we propose a low-energy Hamiltonian to explore the accurate electronic band structure of phosphorene in comparison with those results obtained by density-functional simulations. We explain the effect of the…
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We apply the generalized Boltzmann theory to describe thermoelectric transport properties of monolayer phosphorene in the presence of short- and long-range charged impurity interactions. First, we propose a low-energy Hamiltonian to explore the accurate electronic band structure of phosphorene in comparison with those results obtained by density-functional simulations. We explain the effect of the coupling between the conduction and valence bands on the thermoelectric properties. We show that the electric conductivity of phosphorene is highly anisotropic, while the Seebeck coefficient and figure of merit, without being influenced via either the presence or absence of the coupling term, are nearly isotropic. Furthermore, we demonstrate that the conductivity for the $n$ type of doping is more influenced by the coupling term than that of the $p$ type. Along with thermopower sign change, profound thermoelectric effects can be achieved.
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Submitted 26 January, 2017; v1 submitted 29 August, 2016;
originally announced August 2016.
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Neuronal Avalanches: Where Temporal Complexity and Criticality Meet
Authors:
Mohammad Dehghani Habibabadi,
Marzieh Zare,
Farhad Shahbazi,
Javad Usefie-Mafahim,
Paolo Grigolini
Abstract:
The model of the current paper is an extension of a previous publication, wherein we used the leaky integrate-and-fire model on a regular lattice with periodic boundary conditions, and introduced the temporal complexity as a genuine signature of criticality. In that work, the power-law distribution of neural avalanches was manifestation of supercriticality rather than criticality. Here, however, w…
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The model of the current paper is an extension of a previous publication, wherein we used the leaky integrate-and-fire model on a regular lattice with periodic boundary conditions, and introduced the temporal complexity as a genuine signature of criticality. In that work, the power-law distribution of neural avalanches was manifestation of supercriticality rather than criticality. Here, however, we show that continuous solution of the model and replacing the stochastic noise with a Gaussian zero-mean noise leads to the coincidence of power-law display of temporal complexity and spatiotemporal patterns of neural avalanches at the critical point. We conclude that the source of inconsistency may in fact be a numerical artifact originated by the discrete description of the model, which may imply slow numerical convergence of avalanche distribution compared to temporal complexity.
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Submitted 13 December, 2016; v1 submitted 29 August, 2016;
originally announced August 2016.
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Strain-induced topological phase transition in phosphorene and phosphorene nanoribbons
Authors:
E. Taghizadeh Sisakht,
F. Fazileh,
M. H. Zare,
M. Zarenia,
F. M. Peeters
Abstract:
Using the tight-binding (TB) approximation with inclusion of the spin-orbit interaction, we predict a topological phase transition in the electronic band structure of phosphorene in the presence of axial strains. We derive a low-energy TB Hamiltonian that includes the spin-orbit interaction for bulk phosphorene. Applying a compressive biaxial in-plane strain and perpendicular tensile strain in ran…
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Using the tight-binding (TB) approximation with inclusion of the spin-orbit interaction, we predict a topological phase transition in the electronic band structure of phosphorene in the presence of axial strains. We derive a low-energy TB Hamiltonian that includes the spin-orbit interaction for bulk phosphorene. Applying a compressive biaxial in-plane strain and perpendicular tensile strain in ranges where the structure is still stable leads to a topological phase transition. We also examine the influence of strain on zigzag phosphorene nanoribbons (zPNRs) and the formation of the corresponding protected edge states when the system is in the topological phase. For zPNRs up to a width of 100 nm the energy gap is at least three orders of magnitude larger than the thermal energy at room temperature.
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Submitted 18 August, 2016;
originally announced August 2016.
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Topological phase and edge states dependence of the RKKY interaction in zigzag silicene nanoribbon
Authors:
Moslem Zare,
Fariborz Parhizgar,
Reza Asgari
Abstract:
We propose versatile materials based on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in a zigzag silicene nanoribbon (ZSNR) on half filling in the presence of an out-of-plane electric field. We show that the topological phase transition in the band dispersion of ZSNR can be probed by using the RKKY interaction. We find that, due to the zero-energy edge states of the ZSNR, the exchange coup…
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We propose versatile materials based on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in a zigzag silicene nanoribbon (ZSNR) on half filling in the presence of an out-of-plane electric field. We show that the topological phase transition in the band dispersion of ZSNR can be probed by using the RKKY interaction. We find that, due to the zero-energy edge states of the ZSNR, the exchange coupling is significantly enhanced when the impurities are located on the zigzag edges, and also explore that the strength of the interaction in the topological insulator phase is much greater than that when the system is in the band insulator region. We present a model to investigate the phase of a system of two magnetic impurities located on the edge of the ZSNR and find that three different magnetic phases, spiral, ferromagnetic, and anti-ferromagnetic, are possible for different values of the electric field. This electrical tunability of the magnetic phases in silicene can be explored by using current experimental techniques and can be of interest in the field of spintronics.
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Submitted 3 August, 2016; v1 submitted 3 July, 2015;
originally announced July 2015.
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Valley- and spin-filter in monolayer MoS$_2$
Authors:
Leyla Majidi,
Moslem Zare,
Reza Asgari
Abstract:
We propose a valley- and spin-filter based on a normal/ferromagnetic/normal molybdenum disulfide (MoS$_2$) junction where the polarizations of the valley and the spin can be inverted by reversing the direction of the exchange field in the ferromagnetic region. By using a modified Dirac Hamiltonian and the scattering formalism, we find that the polarizations can be tuned by applying a gate voltage…
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We propose a valley- and spin-filter based on a normal/ferromagnetic/normal molybdenum disulfide (MoS$_2$) junction where the polarizations of the valley and the spin can be inverted by reversing the direction of the exchange field in the ferromagnetic region. By using a modified Dirac Hamiltonian and the scattering formalism, we find that the polarizations can be tuned by applying a gate voltage and changing the exchange field in the structure. We further demonstrate that the presence of a topological term ($β$) in the Hamiltonian results in an enhancement or a reduction of the charge conductance depending on the value of the exchange field.
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Submitted 11 October, 2014;
originally announced October 2014.
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Scaling laws for band gaps of phosphorene nanoribbons: A tight-binding calculation
Authors:
Esmaeil Taghizadeh Sisakht,
Mohammad H. Zare,
Farhad Fazileh
Abstract:
In this study, we analyze the band structure, the state characterization, and electronic transport of monolayer black phosphorus (phosphorene) zigzag nanoribbons (zPNRs) and armchair nanoribbons (aPNRs), using five-parameter tight-binding (TB) approximation. In zPNRs, the ratio of the two dominant hopping parameters indicates the possibility of a relativistic dispersion relation and the existence…
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In this study, we analyze the band structure, the state characterization, and electronic transport of monolayer black phosphorus (phosphorene) zigzag nanoribbons (zPNRs) and armchair nanoribbons (aPNRs), using five-parameter tight-binding (TB) approximation. In zPNRs, the ratio of the two dominant hopping parameters indicates the possibility of a relativistic dispersion relation and the existence of a pair of separate quasi-flat bands at the Fermi level. Moreover, the corresponding states are edge localized if their bands are well separated from the valence and conduction bands. We also investigated the scaling laws of the band gaps versus ribbon widths for the armchair and zigzag phosphorene nanoribbons. In aPNRs, the transverse electric field along the ribbon width enhances the band gap closure by shifting the energy of the valence and conduction band edge states. For zPNRs, a gap occurs at the middle of the relatively degenerate quasi-flat bands; thus, these ribbons are a promising candidate for future field-effect transistors.
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Submitted 14 August, 2015; v1 submitted 26 August, 2014;
originally announced August 2014.
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Valence Bond Phases in $S=1/2$ Kane-Mele-Heisenberg Model
Authors:
Mohammad H. Zare,
Hamid Mosadeq,
Farhad Shahbazi,
S. A. Jafari
Abstract:
The phase diagram of Kane-Mele-Heisenberg (KMH) model in classical limit~\cite{zare}, contains disordered regions in the coupling space, as the result of to competition among different terms in the Hamiltonian, leading to frustration in finding a unique ground state. In this work we explore the nature of these phase in the quantum limit, for a $S=1/2$. Employing exact diagonalization (ED) in…
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The phase diagram of Kane-Mele-Heisenberg (KMH) model in classical limit~\cite{zare}, contains disordered regions in the coupling space, as the result of to competition among different terms in the Hamiltonian, leading to frustration in finding a unique ground state. In this work we explore the nature of these phase in the quantum limit, for a $S=1/2$. Employing exact diagonalization (ED) in $S_z$ and nearest neighbor valence bond (NNVB) bases, bond and plaquette valence bond mean field theories, We show that the disordered regions are divided into ordered quantum states in the form of plaquette valence bond crystal(PVBC) and staggered dimerized (SD) phases.
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Submitted 25 July, 2014;
originally announced July 2014.
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Zero Temperature Phase Diagram of the Classical Kane-Mele-Heisenberg Model
Authors:
Mohammad Hossein Zare,
Farhad Fazileh,
Farhad Shahbazi
Abstract:
The classical phase diagram of the Kane-Mele-Heisenberg model is obtained by three complementary methods: Luttinger-Tisza, variational minimization, and the iterative minimization method. Six distinct phases were obtained in the space of the couplings. Three phases are commensurate with long-range ordering, planar N{é}el states in horizontal plane (phase.I), planar states in the plane vertical to…
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The classical phase diagram of the Kane-Mele-Heisenberg model is obtained by three complementary methods: Luttinger-Tisza, variational minimization, and the iterative minimization method. Six distinct phases were obtained in the space of the couplings. Three phases are commensurate with long-range ordering, planar N{é}el states in horizontal plane (phase.I), planar states in the plane vertical to the horizontal plane (phase.VI) and collinear states normal to the horizontal plane (phase.II). However the other three, are infinitely degenerate due to the frustrating competition between the couplings, and characterized by a manifold of incommensurate wave-vectors. These phases are, planar helical states in horizontal plane (phase.III), planar helical states in a vertical plane (phase.IV) and non-coplanar states (phase.V). Employing the linear spin-wave analysis, it is found that the quantum fluctuations select a set of symmetrically equivalent states in phase.III, through the quantum order-by-disorder mechanism. Based on some heuristic arguments is argued that the same scenario may also occur in the other two frustrated phases VI and V.
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Submitted 28 June, 2013; v1 submitted 10 April, 2013;
originally announced April 2013.
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Anderson Transition in Disordered Bilayer Graphene
Authors:
M. H. Zare,
Mohsen Amini,
Farhad Shahbazi,
S. A. Jafari
Abstract:
Employing the Kernel Polynomial method (KPM), we study the electronic properties of the graphene bilayers in the presence of diagonal disorder, within the tight-binding approximation. The KPM method enables us to calculate local density of states (LDOS) without need to exactly diagonalize the Hamiltonian. We use the geometrical averaging of the LDOS's at different lattice sites as a criterion to…
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Employing the Kernel Polynomial method (KPM), we study the electronic properties of the graphene bilayers in the presence of diagonal disorder, within the tight-binding approximation. The KPM method enables us to calculate local density of states (LDOS) without need to exactly diagonalize the Hamiltonian. We use the geometrical averaging of the LDOS's at different lattice sites as a criterion to distinguish the localized states from extended ones. We find that bilayer graphene undergoes Anderson metal-insulator transition at a critical value of disorder strength.
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Submitted 23 February, 2010;
originally announced February 2010.