Showing 1–50 of 321 results for author: Das, P

Observation of disorder-induced superfluidity

Authors: Nicole Ticea, Elias Portoles, Eliott Rosenberg, Alexander Schuckert, Aaron Szasz, Bryce Kobrin, Nicolas Pomata, Pranjal Praneel, Connie Miao, Shashwat Kumar, Ella Crane, Ilya Drozdov, Yuri Lensky, Sofia Gonzalez-Garcia, Thomas Kiely, Dmitry Abanin, Amira Abbas, Rajeev Acharya, Laleh Aghababaie Beni, Georg Aigeldinger, Ross Alcaraz, Sayra Alcaraz, Markus Ansmann, Frank Arute, Kunal Arya , et al. (277 additional authors not shown)

Abstract: The emergence of states with long-range correlations in a disordered landscape is rare, as disorder typically suppresses the particle mobility required for long-range coherence. But when more than two energy levels are available per site, disorder can induce resonances that locally enhance mobility. Here we explore phases arising from the interplay between disorder, kinetic energy, and interaction… ▽ More The emergence of states with long-range correlations in a disordered landscape is rare, as disorder typically suppresses the particle mobility required for long-range coherence. But when more than two energy levels are available per site, disorder can induce resonances that locally enhance mobility. Here we explore phases arising from the interplay between disorder, kinetic energy, and interactions on a superconducting processor with qutrit readout and control. Compressibility measurements distinguish an incompressible Mott insulator from surrounding compressible phases and reveal signatures of glassiness, reflected in non-ergodic behavior. Spatially-resolved two-point correlator measurements identify regions of the phase diagram with a non-vanishing condensate fraction. We also visualize the spectrum by measuring the dynamical structure factor. A linearly-dispersing phonon mode materializes in the superfluid, appearing even when disorder is introduced to the clean Mott insulator. Our results provide strong experimental evidence for disorder-induced superfluidity. △ Less

Submitted 24 December, 2025; originally announced December 2025.

Conservation laws and chaos propagation in a non-reciprocal classical magnet

Authors: Nisarg Bhatt, Purnendu Das, Subroto Mukerjee, Sriram Ramaswamy

Abstract: We study a nonreciprocal generalization [EPL 60, 418 (2002)] of the classical Heisenberg spin chain, in which the exchange coupling is nonsymmetric, and show that it displays a ballistic spreading of chaos as measured by the decorrelator. We show that the interactions are reciprocal in terms of transformed variables, with conserved quantities that can be identified as magnetization and energy, wit… ▽ More We study a nonreciprocal generalization [EPL 60, 418 (2002)] of the classical Heisenberg spin chain, in which the exchange coupling is nonsymmetric, and show that it displays a ballistic spreading of chaos as measured by the decorrelator. We show that the interactions are reciprocal in terms of transformed variables, with conserved quantities that can be identified as magnetization and energy, with a Poisson-bracket algebra and Hamiltonian dynamics. For strictly antisymmetric couplings in the original model the conserved quantities diffuse, the decorrelator spreads symmetrically, and a simple hydrodynamic theory emerges. The general case in which the interaction has symmetric and antisymmetric parts presents complexities in the limit of large scales. Ballistic propagation of chaos survives the inclusion of interactions beyond nearest neighbours, but the conservation laws in general do not. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Intralayer antiferromagnetism in two-dimensional van der Waals magnet Fe$_3$GeTe$_2$

Authors: Neesha Yadav, Shivani Kumawat, Sandeep, Brajesh Kumar Mani, Pintu Das

Abstract: For the van der Waals magnet Fe$_3$GeTe$_2$, although a ferromagnetic ground state has been reported, there are also reports of complex magnetic behavior suggesting coexistence of ferromagnetism and antiferromagnetism due to the intricate interaction between Fe$^{+3}$ and Fe$^{+2}$ ions in this system. The exact nature of the interactions and the origin of antiferromagnetism are still under debate… ▽ More For the van der Waals magnet Fe$_3$GeTe$_2$, although a ferromagnetic ground state has been reported, there are also reports of complex magnetic behavior suggesting coexistence of ferromagnetism and antiferromagnetism due to the intricate interaction between Fe$^{+3}$ and Fe$^{+2}$ ions in this system. The exact nature of the interactions and the origin of antiferromagnetism are still under debate. Here, we report the observation of signature of ferromagnetic and antiferromagnetic couplings between different Fe-ions in the anomalous Hall effect measured for devices of mechanically exfoliated Fe$_3$GeTe$_2$ nano-flakes of thicknesses ranging from\,$\sim$\,15-20 layers. The temperature-dependent anomalous Hall effect data reveal two sharp step-like switchings at low temperature ($T\lesssim150\,$K). Our detailed analyses suggest the step-like sharp switchings in anomalous Hall resistance are due to the magnetization reversal behavior of different Fe-ions in individual layers of Fe$_3$GeTe$_2$. The experimental results can be explained by considering an intra-layer antiferromagnetic coupling between Fe$^{+3}$ and Fe$^{+3}$ ions, whereas intra-layer ferromagnetic coupling between Fe$^{+3}$ and Fe$^{+2}$ in the system. Our experimental results and the analyses are supported by the first-principles calculations for energetics and intralayer as well as interlayer exchange coupling constants. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Comments: 7 figures

Optical contrast-based determination of number of layers for two-dimensional van der Waals magnet Fe$_3$GeTe$_2$

Authors: Neesha Yadav, Sandeep, Pintu Das

Abstract: Recent advances in revealing intrinsic magnetism in two-dimensional (2D) materials have highlighted their potential for future spintronic applications, driven by their novel physical properties, promising for future spintronic devices. In order to explore layer dependent magnetic behavior, in general, mechanically exfoliated flakes from high-quality single crystals are used. It is crucial to deter… ▽ More Recent advances in revealing intrinsic magnetism in two-dimensional (2D) materials have highlighted their potential for future spintronic applications, driven by their novel physical properties, promising for future spintronic devices. In order to explore layer dependent magnetic behavior, in general, mechanically exfoliated flakes from high-quality single crystals are used. It is crucial to determine the number of layers of these materials accurately. In the absence of an efficient and quick method, researchers often rely on atomic force microscopy (AFM) imaging to identify their number of layers. In this work, we report an optical contrast study as a quick and cost-effective technique to determine the number of layers of Fe$_3$GeTe$_2$ (FGT). Here, we observed a linear relationship between the optical contrast (derived from optical microscopic images) observed for mechanically exfoliated FGT nano-flakes and their thickness, as measured by the AFM imaging method. This technique requires no additional equipment; it relies solely on a conventional optical microscope. Additionally, our results reveal a thickness-dependent evolution of the intensity; in contrast, the Raman frequency demonstrates no significant dependence on layer thickness. Also, our studies reveal two additional Raman modes of FGT, at the frequency of 129\,cm$^-1$ \& 190\,cm$^-1$. Both modes show the intensity dependence on the thickness of FGT, same as out-of-plane (A$_{1g}$) Raman modes. △ Less

Submitted 25 November, 2025; originally announced November 2025.

Comments: 4 figures

Conservation in High-field Quantum Transport

Authors: Mukunda P. Das, Frederick Green

Abstract: We give a short overview of the role of microscopic conservation in charge transport at small scales, and at driving fields beyond the linear-response limit. As a practical example we recall the measurement and theory of interband coupling effects in a quantum point contact driven far from equilibrium. We give a short overview of the role of microscopic conservation in charge transport at small scales, and at driving fields beyond the linear-response limit. As a practical example we recall the measurement and theory of interband coupling effects in a quantum point contact driven far from equilibrium. △ Less

Submitted 25 November, 2025; originally announced November 2025.

Comments: Brief recap of quantum kinetics for 1D transport: 9pp, 6 figures

Journal ref: Condens. Matter 10(4), 59 (2025)

Layer breathing Raman mode in two-dimensional van der Waals material $\mathrm{Cr_2Ge_2Te_6}$

Authors: Nilesh Choudhury, Sandeep, Neesha Yadav, Mayank Shukla, Pintu Das

Abstract: Two-dimensional (2D) van der Waals (vdW) magnetic materials have emerged as key materials for next-generation magneto-electric and spintronic devices, where understanding the relationship between layer number, lattice dynamics, and magnetic interactions is very important. In this work, we report the observation of the layer breathing mode (LBM) in few-layer $\mathrm{Cr_2Ge_2Te_6}$, a ferromagnetic… ▽ More Two-dimensional (2D) van der Waals (vdW) magnetic materials have emerged as key materials for next-generation magneto-electric and spintronic devices, where understanding the relationship between layer number, lattice dynamics, and magnetic interactions is very important. In this work, we report the observation of the layer breathing mode (LBM) in few-layer $\mathrm{Cr_2Ge_2Te_6}$, a ferromagnetic semiconductor with thickness dependent electronic, magnetic and optical properties, using Raman spectroscopy, which serves as a direct fingerprint of interlayer coupling and lattice symmetry. Group-theoretical symmetry analysis confirms that the CGT falls under the non-polar category of layered material. The evolution of the LBM-frequency with increasing layer number (N) reveals a distinct softening trend, characteristic of weakening restoring forces in thicker flakes. By fitting the experimental Raman data using the Linear Chain Model (LCM), we quantitatively extract the interlayer force constant ($\mathrm{K_c}$), providing a measure of the vdW coupling strength between layers. △ Less

Submitted 14 November, 2025; originally announced November 2025.

Exploring the Role of Interfacial Dzyaloshinskii-Moriya Interaction in Write Error Rate Anomalies of Spin-Transfer Torque Magnetic Tunnel Junctions

Authors: Prosenjit Das, Md Mahadi Rajib, Jayasimha Atulasimha

Abstract: The performance and reliability of spin-transfer torque magnetic random-access memory (STT-MRAM) can be compromised by anomalous switching behavior, especially during high-speed operations. One such anomaly, known as the "ballooning effect" is characterized by an unexpected non-monotonic increase in the write error rate (WER) with increase in STT current at specific current pulse durations. In thi… ▽ More The performance and reliability of spin-transfer torque magnetic random-access memory (STT-MRAM) can be compromised by anomalous switching behavior, especially during high-speed operations. One such anomaly, known as the "ballooning effect" is characterized by an unexpected non-monotonic increase in the write error rate (WER) with increase in STT current at specific current pulse durations. In this study, we systematically investigate the role of the interfacial Dzyaloshinskii-Moriya interaction (DMI) on such WER anomaly using micromagnetic simulations of 20 nm and 50 nm magnetic tunnel junctions (MTJs). We show that DMI promotes incoherent magnetization reversal, prolongs the switching time and creates intermediate multidomain states that result in incomplete reversal. At high DMI values, these states persist even under large switching current densities, reproducing ballooning-like anomalies reported experimentally. In contrast, longer pulses overcome these effects by allowing the system sufficient time to reach a stable state. Our findings show that interfacial DMI can play a role in the ballooning effect and point to interfacial engineering as a practical strategy for improving the reliability of next-generation STT-MRAM. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Facile Salt-Assisted Hydrothermal Synthesis of Nanodiamonds from CHO Precursors: Atomic-Scale Mechanistic Insights

Authors: Soumya Pratap Tripathy, Sayan Saha, Saurabh Kumar Gupta, Pallavee Das, Binay Priyadarsan Nayak, Anup Routray, Priya Choudhary, Srihari V, Bitop Maitra, Ashna Reyaz, Anushka Samant, Debopriya Sinha, Kritideepan Parida, Kuna Das, Abhijeet Sahoo, Kunal Pal, Sirsendu Sekhar Ray

Abstract: Hydrothermal synthesis offers an economical and scalable way to produce nanodiamonds under relatively mild, low-pressure and low-temperature conditions. However,its sustainability and the detailed mechanisms behind diamond formation in such environments are still not fully understood. In this work, we designed ten hydrothermal synthesis protocols using different CHO-based molecular precursors cont… ▽ More Hydrothermal synthesis offers an economical and scalable way to produce nanodiamonds under relatively mild, low-pressure and low-temperature conditions. However,its sustainability and the detailed mechanisms behind diamond formation in such environments are still not fully understood. In this work, we designed ten hydrothermal synthesis protocols using different CHO-based molecular precursors containing COOH and OH groups, such as organic acids, polyols, sugars, and polysaccharides.The reactions were carried out at 190 degrees Centigrade in chlorinated, strongly alkaline aqueous solutions with alkali and alkaline-earth metal ions. Using high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, we confirmed the presence of diamond-specific lattice planes and sp3-hybridized carbon structures. Our results show that the type of precursor, its molecular size, and the ionic composition of the solution play key roles in determining the defect patterns and polymorph distribution in the resulting nanodiamonds. Atomic-scale imaging showed both coherent and incoherent transitions from graphite to diamond, along with gradual lattice compression and complex twinning patterns. These observations provide direct insight into how interfacial crystallography and defect dynamics drive diamond formation in aqueous systems. Overall, the study positions hydrothermal synthesis as a sustainable, chemistry-driven, and tunable approach for creating nanodiamonds tailored for applications in quantum technologies, biomedicine, catalysis, and advanced materials. △ Less

Submitted 9 November, 2025; originally announced November 2025.

Comments: Main Manuscript: 9 pages, 1 table, 5 figures; Supplementary Information: 18 pages, 1 table, 26 figures

Vorticity-induced surfing and trapping in porous media

Authors: Pallabi Das, Mirko Residori, Axel Voigt, Suvendu Mandal, Christina Kurzthaler

Abstract: Microorganisms often encounter strong confinement and complex hydrodynamic flows while navigating their habitats. Combining finite-element methods and stochastic simulations, we study the interplay of active transport and heterogeneous flows in dense porous channels. We find that swimming always slows down the traversal of agents across the channel, giving rise to robust power-law tails of their e… ▽ More Microorganisms often encounter strong confinement and complex hydrodynamic flows while navigating their habitats. Combining finite-element methods and stochastic simulations, we study the interplay of active transport and heterogeneous flows in dense porous channels. We find that swimming always slows down the traversal of agents across the channel, giving rise to robust power-law tails of their exit-time distributions. These exit-time distributions collapse onto a universal master curve with a scaling exponent of $\approx 3/2$ across a wide range of packing fractions and motility parameters, which can be rationalized by a scaling relation. We further identify a new motility pattern where agents alternate between surfing along fast streams and extended trapping phases, the latter determining the power-law exponent. Unexpectedly, trapping occurs in the flow backbone itself -- not only at obstacle boundaries -- due to vorticity-induced reorientation in the highly-heterogeneous fluid environment. These findings provide a fundamentally new active transport mechanism with direct implications for biofilm clogging and the design of novel microrobots capable of operating in heterogeneous media. △ Less

Submitted 4 November, 2025; originally announced November 2025.

From data to design: Random forest regression model for predicting mechanical properties of alloy steel

Authors: Samjukta Sinha, Prabhat Das

Abstract: This study investigates the application of Random Forest Regression for predicting mechanical properties of alloy steel-Elongation, Tensile Strength, and Yield Strength-from material composition features including Iron (Fe), Chromium (Cr), Nickel (Ni), Manganese (Mn), Silicon (Si), Copper (Cu), Carbon (C), and deformation percentage during cold rolling. Utilizing a dataset comprising these feature… ▽ More This study investigates the application of Random Forest Regression for predicting mechanical properties of alloy steel-Elongation, Tensile Strength, and Yield Strength-from material composition features including Iron (Fe), Chromium (Cr), Nickel (Ni), Manganese (Mn), Silicon (Si), Copper (Cu), Carbon (C), and deformation percentage during cold rolling. Utilizing a dataset comprising these features, we trained and evaluated the Random Forest model, achieving high predictive performance as evidenced by R2 scores and Mean Squared Errors (MSE). The results demonstrate the model's efficacy in providing accurate predictions, which is validated through various performance metrics including residual plots and learning curves. The findings underscore the potential of ensemble learning techniques in enhancing material property predictions, with implications for industrial applications in material science. △ Less

Submitted 4 November, 2025; originally announced November 2025.

Journal ref: Book Chapter in: Fundamental Frontiers: Expanding Core Sciences, Editors: Dr. P. Saikia, Dr. D. Core, and J. Mahanta, Dr. J. Gogoi, First Edition, October 2024, ISBN: 978-93-91883-69-0

Fluctuations in first passage times and utility of resetting protocol in biochemical systems with two-state toggling

Authors: Hillol Kumar Barman, Pathik Das, Syed Yunus Ali

Abstract: Interesting theoretical problems of target search or threshold crossing, formally known as {\it first passage}, often arise in both diffusive transport problems as well as problems of chemical reaction kinetics. We study three systems following different chemical kinetics, and are special as they {\it toggle between two states}: (i) a population dynamics of cells with auto-catalytic birth and inte… ▽ More Interesting theoretical problems of target search or threshold crossing, formally known as {\it first passage}, often arise in both diffusive transport problems as well as problems of chemical reaction kinetics. We study three systems following different chemical kinetics, and are special as they {\it toggle between two states}: (i) a population dynamics of cells with auto-catalytic birth and intermittent toxic chemical-induced forced death, (ii) a bond cluster model representing membrane adhesion to extracellular matrix under a fluctuating load, and (iii) a model of gene transcription with a regulated promoter switching between active and inactive states. Each of these systems has a target state to attain, which defines a first passage problem -- namely, population becoming extinct, complete membrane detachment, or mRNA count crossing a threshold. We study the fluctuations in first passage time and show that it is interestingly {\it non-monotonic} in all these cases, with increasing strength of bias towards the target. We also study suitable {\it stochastic resetting} protocols to expedite first passage for these systems, and show that there is a re-entrant transition of the efficacy of this protocol in all the three cases, as a function of the bias. The exact analytical condition for these transitions predicted in earlier literature is verified here through simulations. △ Less

Submitted 21 October, 2025; originally announced October 2025.

Journal ref: J. Phys. Chem. B 2025

Observation of Crystalline Nonlocal Volume Plasmon Waves

Authors: Sathwik Bharadwaj, Makoto Schreiber, Jungho Mun, Sam Ruttiman, Pronoy Das, Misa Hayashida, Marek Malac, Peter Nordlander, Zubin Jacob

Abstract: In plasmonics, nonlocal effects arise when the material response to optical excitations is strongly dependent on the spatial correlations of the excitation. It is well known that a classical free electron gas system supports local Drude volume plasmon waves. Whereas a compressible quantum electron gas system sustains hydrodynamic volume plasmons with nonlocal dispersion isotropic across all high-s… ▽ More In plasmonics, nonlocal effects arise when the material response to optical excitations is strongly dependent on the spatial correlations of the excitation. It is well known that a classical free electron gas system supports local Drude volume plasmon waves. Whereas a compressible quantum electron gas system sustains hydrodynamic volume plasmons with nonlocal dispersion isotropic across all high-symmetry directions. Here, distinct from Drude and Hydrodynamic plasmon waves, we present the first observation of crystalline nonlocal volume plasmon waves. We use transmission-based momentum-resolved electron energy loss spectroscopy to measure the volume plasmon dispersion of silicon along all the fundamental symmetry axes, up to high momentum values ($q \sim 0.7$ reciprocal lattice units). We show that crystalline nonlocal plasmon waves have a prominent anisotropic dispersion with higher curvature along the light-mass ($ΓK$ \& $ΓL$) axes, compared to the heavy-mass ($ΓX$) axis. We unveil the origin of this phenomenon by experimentally extracting the anisotropic Fermi velocities of silicon. Our work highlights an exquisite nonlocality-induced anisotropy of volume plasmon waves, providing pathways for probing many-body quantum effects at extreme momenta. △ Less

Submitted 8 October, 2025; originally announced October 2025.

Thermal gradient-driven skyrmion dynamics with near-zero skyrmion Hall angle

Authors: Yogesh Kumar, Hurmal Saren, Pintu Das

Abstract: Thermal gradient driven skyrmion dynamics offers a promising route toward green spintronics, enabling the utilization of waste heat for information transport and processing. Using micromagnetic simulations, we investigate Neel skyrmions in a Co-Pt bilayer nanoracetrack and demonstrate that stochastic torques induced by a thermal gradient drive skyrmion motion toward the hotter region with a nearly… ▽ More Thermal gradient driven skyrmion dynamics offers a promising route toward green spintronics, enabling the utilization of waste heat for information transport and processing. Using micromagnetic simulations, we investigate Neel skyrmions in a Co-Pt bilayer nanoracetrack and demonstrate that stochastic torques induced by a thermal gradient drive skyrmion motion toward the hotter region with a nearly vanishing Hall angle. The dynamics depends sensitively on intrinsic material parameters - the skyrmion velocity decreases with increasing damping constant, increases with stronger thermal gradients, and varies systematically with saturation magnetization, interfacial DMI strength, and uniaxial out of plane anisotropy. Importantly, we identify a specific range of material parameters within which the skyrmion velocity changes sharply while the Hall angle remains strongly suppressed, saturating near zero. This comprehensive parameter-dependent study establishes a universal design framework for minimizing the Hall effect in thermal gradient driven spintronic systems. △ Less

Submitted 8 October, 2025; originally announced October 2025.

Comments: 5 figures

Superconducting pairing symmetries in charge-ordered kagomé metals

Authors: Pujita Das, Parth Bahuguna, Tulika Maitra, Narayan Mohanta

Abstract: We investigate the superconducting state in a kagomé lattice, with intertwined charge order and time-reversal symmetry-breaking loop current, using self-consistent Bogoliubov-de Gennes formalism to find the emergent pairing symmetries. Using local and nearest-neighbor attractive interactions, treated within Hartree-Fock mean-field approximation, we obtain all possible pairing symmetries in positio… ▽ More We investigate the superconducting state in a kagomé lattice, with intertwined charge order and time-reversal symmetry-breaking loop current, using self-consistent Bogoliubov-de Gennes formalism to find the emergent pairing symmetries. Using local and nearest-neighbor attractive interactions, treated within Hartree-Fock mean-field approximation, we obtain all possible pairing symmetries in position space. Our findings indicate that the uniform $s$-wave symmetry, arising in the absence of the charge order and the loop current, modifies to a pair density wave of $s$-wave symmetry of 2$\times$2 lattice periodicity in the presence of the charge order, and a chiral pair density wave of $d_{x^2-y^2}\!+\!id_{xy}$-wave symmetry of the same 2$\times$2 periodicity in the presence of the charge order and loop current order, in both onsite and nearest-neighbor channels. In the absence of inversion symmetry, such as in the thin-film geometry, Rashba spin-orbit coupling appears, inducing an additional nearest-neighbor triplet $p_x\pm ip_y$-wave pairing. The results are relevant to superconductivity found in $A$V$_{3}$Sb$_{5}$ ($A$ = K, Rb, Cs), coexisting with a charge order that breaks time-reversal symmetry. We discuss fingerprints of these different pairing symmetries in scanning tunneling microscopy experiments. △ Less

Submitted 4 September, 2025; originally announced September 2025.

Comments: 15 pages, 10 figures

Anisotropic exciton-polaritons reveal non-Hermitian topology in van der Waals materials

Authors: Devarshi Chakrabarty, Avijit Dhara, Pritam Das, Kritika Ghosh, Ayan Roy Chaudhuri, Sajal Dhara

Abstract: Topological band theory has expanded into various domains in applied physics, offering significant potential for future technologies. Recent developments indicate that unique bulk band topology perceived for electrons can be realized in a system of light-matter quasiparticles with reduced crystal symmetry utilizing tunable light-matter interaction. In this work we realize topologically non-trivial… ▽ More Topological band theory has expanded into various domains in applied physics, offering significant potential for future technologies. Recent developments indicate that unique bulk band topology perceived for electrons can be realized in a system of light-matter quasiparticles with reduced crystal symmetry utilizing tunable light-matter interaction. In this work we realize topologically non-trivial energy band dispersion of exciton-polaritons confined in two-dimensional anisotropic materials inside an optical microcavity, and show the emergence of exceptional points (EPs) due to non-Hermitian topology arising from excitonic dipole oscillators with finite quasiparticle lifetime. Fourier-plane imaging reveals two pairs of EPs connected by bulk Fermi arcs for each of the transverse electric and magnetic polarized modes. An anisotropic Lorentz oscillator model captures the exact band dispersion observed in our experiment in two-dimensional momentum space. Our findings establish anisotropic two-dimensional materials as a platform for exploring non-Hermitian topological physics, with implications for polarization-controlled optical technologies. △ Less

Submitted 12 August, 2025; originally announced August 2025.

Comments: Main text: 8 pages, 5 figures; Supplementary material: 6 pages, 5 figures

Giant Resonance Raman Scattering via Anisotropic Excitons in ReS2

Authors: Pritam Das, Devarshi Chakrabarty, Neha Gill, Sajal Dhara

Abstract: Anisotropic two-dimensional (2D) semiconductors recently have emerged as a promising platform for polarization-controlled Raman amplification. In this study, we probe energy-dependent resonant Raman scattering in few layer ReS2 under different polarization configurations. We identify two distinct excitation regimes, each characterized by a resonance condition where either the pump or the Stokes ph… ▽ More Anisotropic two-dimensional (2D) semiconductors recently have emerged as a promising platform for polarization-controlled Raman amplification. In this study, we probe energy-dependent resonant Raman scattering in few layer ReS2 under different polarization configurations. We identify two distinct excitation regimes, each characterized by a resonance condition where either the pump or the Stokes photon energy aligns with an excitonic transition. A two-order-of-magnitude enhancement in Raman intensity is observed when the pump energy is tuned near the exciton resonance. Under Stokes-resonant conditions, additional Raman lines accompanied by excitonic photoluminescence are observed, suggesting the participation of non-Bloch intermediate states in the scattering process. These findings shed light into the influence of excitons in modulating nonlinear optical phenomena in anisotropic 2D materials, offering valuable insights for the design of tunable photonic and optoelectronic devices based on anisotropic layered materials. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: Main text: 15 pages, 4 figures, Supporting information: 5 pages, 4 figures

Velocity Distribution and Diffusion of an Athermal Inertial Run-and-Tumble Particle in a Shear-Thickening Medium

Authors: Subhanker Howlader, Sayantan Mondal, Prasenjit Das

Abstract: We study the dynamics of an athermal inertial run-and-tumble particle moving in a shear-thickening medium in $d=1$. The viscosity of the medium is represented by a nonlinear function $f(v)\sim\tan(v)$, while a symmetric dichotomous noise of strength $Σ$ and flipping rate $λ$ models the activity of the particle. Starting from the Fokker-Planck~(FP) equation for the time-dependent probability distri… ▽ More We study the dynamics of an athermal inertial run-and-tumble particle moving in a shear-thickening medium in $d=1$. The viscosity of the medium is represented by a nonlinear function $f(v)\sim\tan(v)$, while a symmetric dichotomous noise of strength $Σ$ and flipping rate $λ$ models the activity of the particle. Starting from the Fokker-Planck~(FP) equation for the time-dependent probability distribution $W_{\pmΣ}(v, t)$ of the particle's velocity $v$ at time $t$ and the active force is $\pmΣ$, we analytically derive the steady-state velocity distribution function $W_s(v)$ and a quadrature expression for the effective diffusion coefficient $D_{\rm eff}$. For a fixed $Σ$, $W_s(v)$ undergoes multiple transitions with varying $λ$, and we have identified the corresponding transition points. We then numerically compute $W_s(v)$, the mean-squared velocity $\langle v^2\rangle(t)$, and the diffusion coefficient $D_{\rm eff}$, all of which show excellent agreement with the analytical results in the steady-state. Finally, we test the robustness of the transitions in $W_s(v)$ by considering an alternative $f(v)$ function that also capture the shear-thickening behavior of the medium. △ Less

Submitted 16 July, 2025; originally announced July 2025.

Comments: 17 Pages, 6 Figures, Accepted in Phys. Rev. E

Journal ref: Phys. Rev. E 112, 025403 (2025)

A new method to find exact solution of nonlinear ordinary differential equations: Application to derive thermophoretic waves in graphene sheets

Authors: Prakash Kumar Das

Abstract: This article proposes a novel approach for determining exact solutions to nonlinear ordinary differential equations. The recommended iterative method provides the solution via a rapidly converging series that readily approaches a closed form solution. The proposed approach is very efficient and essentially perfect for determining exact solutions of nonlinear equations. To demonstrate the effective… ▽ More This article proposes a novel approach for determining exact solutions to nonlinear ordinary differential equations. The recommended iterative method provides the solution via a rapidly converging series that readily approaches a closed form solution. The proposed approach is very efficient and essentially perfect for determining exact solutions of nonlinear equations. To demonstrate the effectiveness of this method, we examined the extended (2 + 1) dimensional equation for thermophoretic motion, which is based on wrinkle wave movements in graphene sheets supported by a substrate. The implementation of the suggested approach effectively yielded closed-form solutions in terms of exponential functions, hyperbolic functions, trigonometric functions, algebraic functions, and Jacobi elliptic functions, respectively. Three generated solutions illustrated to examine the characteristics of thermophoretic waves in graphene sheets. The proposed method's benefits and drawbacks are also examined. Consequently, unlike previous solutions obtained via the variation of parameters method for nonlinear issues, the solutions presented here are exact and unique. △ Less

Submitted 21 June, 2025; originally announced July 2025.

Comments: 3 figures

Quantum Theory of Optical Spin Texture in Chiral Tellurium Lattice

Authors: Pronoy Das, Sathwik Bharadwaj, Jungho Mun, Xueji Wang, Junsuk Rho, Zubin Jacob

Abstract: The absence of inversion symmetry in chiral tellurium (Te) creates exotic spin textures within its electron waves. However, understanding textured optical waves within Te remains a challenge due to the semi-classical limitations of long-wavelength approximation. To unveil these textured optical waves, we develop a spin-resolved deep-microscopic optical bandstructure for Te analogous to its electro… ▽ More The absence of inversion symmetry in chiral tellurium (Te) creates exotic spin textures within its electron waves. However, understanding textured optical waves within Te remains a challenge due to the semi-classical limitations of long-wavelength approximation. To unveil these textured optical waves, we develop a spin-resolved deep-microscopic optical bandstructure for Te analogous to its electronic counterpart. We demonstrate that the degeneracies in this optical bandstructure is lifted by the twisted lattice of Te, which induces optical gyrotropy. Our theory shows excellent agreement with experimental optical gyrotropy measurements. At the lattice level, we reveal that the chirality of Te manifests as deep-microscopic optical spin texture within the optical wave. Our framework uncovers the finite-momentum origin of optical activity and provides a microscopic basis for light-matter interactions in chiral crystalline materials. △ Less

Submitted 30 September, 2025; v1 submitted 20 June, 2025; originally announced June 2025.

Theory of Angle Resolved Photoemission Spectroscopy of Altermagnetic Mott Insulators

Authors: Lorenzo Lanzini, Purnendu Das, Michael Knap

Abstract: Altermagnetism has emerged as an unconventional form of collinear magnetism with spatial rotational symmetries, that give rise to strongly spin-split bands despite of an underlying fully-compensated antiferromagnetic order. Here, we develop a theory for the Angle Resolved Photoemission Spectroscopy (ARPES) response of altermagnetic Mott insulators. Crucially, the spectrum does not simply reflect t… ▽ More Altermagnetism has emerged as an unconventional form of collinear magnetism with spatial rotational symmetries, that give rise to strongly spin-split bands despite of an underlying fully-compensated antiferromagnetic order. Here, we develop a theory for the Angle Resolved Photoemission Spectroscopy (ARPES) response of altermagnetic Mott insulators. Crucially, the spectrum does not simply reflect the non-interacting band structure, but instead a magnetic polaron is formed at low energies, that can be interpreted as a spinon-holon bound state. We develop a spinon-holon parton theory and predict a renormalized bandwidth that we confirm by tensor network simulations. We analyze the characteristic spin-split spectrum and identify a spin-dependent spectral weight of the magnetic polaron, resulting from the altermagnetic symmetry. Our work paves the way for a systematic study of doping effects and correlation phenomena in altermagnetic Mott insulators. △ Less

Submitted 3 June, 2025; originally announced June 2025.

Comments: 5+5 pages, 4+5 figures

Ultraslow Growth of Domains in a Random-Field System With Correlated Disorder

Authors: Subhanker Howlader, Prasenjit Das, Manoj Kumar

Abstract: We study domain growth kinetics in a random-field system in the presence of a spatially correlated disorder $h_{i}(\vec r)$ after an instantaneous quench at a finite temperature $T$ from a random initial state corresponding to $T=\infty$. The correlated disorder field $h_{i}(\vec r)$ arises due to the presence of magnetic impurities, decaying spatially in a power-law fashion. We use Glauber spin-f… ▽ More We study domain growth kinetics in a random-field system in the presence of a spatially correlated disorder $h_{i}(\vec r)$ after an instantaneous quench at a finite temperature $T$ from a random initial state corresponding to $T=\infty$. The correlated disorder field $h_{i}(\vec r)$ arises due to the presence of magnetic impurities, decaying spatially in a power-law fashion. We use Glauber spin-flip dynamics to simulate the kinetics at the microscopic level. The system evolves via the formation of ordered magnetic domains. We characterize the morphology of domains using the equal-time correlation function $C(r,t)$ and structure factor $S(k,t)$. In the large-$k$ limit, $S(k, t)$ obeys Porod's law: $S(k, t)\sim k^{-(d+1)}$. The average domain size $L(t)$ asymptotically follows \textit{double logarithmic growth behavior}. △ Less

Submitted 11 May, 2025; originally announced May 2025.

Comments: 17 Pages, 10 Figures, Accepted in Physica A

Exploring unconventional superconductivity in PdTe via Point Contact Spectroscopy

Authors: Pritam Das, Sulagna Dutta, Saurav Suman, Amit Vashist, Bibek Ranjan Satapathy, John Jesudasan, Suvankar Chakraverty, Rajdeep Sensarma, Pratap Raychaudhuri

Abstract: Palladium Telluride (PdTe), a non-layered intermetallic crystalline compound, has captured attention for its unique superconducting properties and strong spin-orbit coupling. In this work, we investigate the superconducting state of PdTe using point-contact Andreev reflection (PCAR) spectroscopy. The experimental data are analyzed using the Blonder-Tinkham-Klapwijk (BTK) model for s, p and d wave… ▽ More Palladium Telluride (PdTe), a non-layered intermetallic crystalline compound, has captured attention for its unique superconducting properties and strong spin-orbit coupling. In this work, we investigate the superconducting state of PdTe using point-contact Andreev reflection (PCAR) spectroscopy. The experimental data are analyzed using the Blonder-Tinkham-Klapwijk (BTK) model for s, p and d wave symmetries. Our results reveal clear evidence of unconventional superconductivity. The superconducting gap showing features consistent with either p-wave or d-wave pairing symmetries but cannot be fitted with s-wave symmetry. The observed anisotropic gap structure and deviations from conventional BCS behaviour highlight the complex nature of the pairing interactions in PdTe. These findings provide strong evidence of unconventional pairing symmetry in this material. △ Less

Submitted 8 May, 2025; originally announced May 2025.

Phase Separation in Active Binary Mixtures With Chemical Reaction

Authors: Sayantan Mondal, Prasenjit Das

Abstract: We study motility-induced phase separation~(MIPS) in active AB binary mixtures undergoing the chemical reaction $A \rightleftharpoons B$. Starting from the evolution equations for the density fields $ρ_i(\vec r, t)$ describing MIPS, we phenomenologically incorporate the effects of the reaction through the reaction rate $Γ$ into the equations. The steady-state domain morphologies depend on $Γ$ and… ▽ More We study motility-induced phase separation~(MIPS) in active AB binary mixtures undergoing the chemical reaction $A \rightleftharpoons B$. Starting from the evolution equations for the density fields $ρ_i(\vec r, t)$ describing MIPS, we phenomenologically incorporate the effects of the reaction through the reaction rate $Γ$ into the equations. The steady-state domain morphologies depend on $Γ$ and the relative activity of the species, $Δ$. For a sufficiently large $Γ$ and $Δ\ne 1$, the more active component of the mixture forms a droplet morphology. We characterize the morphology of domains by calculating the equal-time correlation function $C(r, t)$ and the structure factor $S(k, t)$, exhibiting scaling violation. The average domain size, $L(t)$, follows a diffusive growth as $L(t)\sim t^{1/3}$ before reaching the steady state domain size, $L_{\rm ss}$. Additionally, $L_{\rm ss}$ shows the scaling relation $L_{\rm ss}\simΓ^{-1/4}$, independent of $Δ$. △ Less

Submitted 16 April, 2025; originally announced April 2025.

Comments: 16 Pages, 7 Figures, Accepted to Soft Matter

Velocity Distribution and Diffusion of an Athermal Inertial Run-and-Tumble Particle in a Shear-Thinning Medium

Authors: Sayantan Mondal, Prasenjit Das

Abstract: We study the dynamics of an athermal inertial active particle moving in a shear-thinning medium in $d=1$. The viscosity of the medium is modeled using a Coulomb-tanh function, while the activity is represented by an asymmetric dichotomous noise with strengths $-Δ$ and $μΔ$, transitioning between these states at a rate $λ$. Starting from the Fokker-Planck~(FP) equation for the time-dependent probab… ▽ More We study the dynamics of an athermal inertial active particle moving in a shear-thinning medium in $d=1$. The viscosity of the medium is modeled using a Coulomb-tanh function, while the activity is represented by an asymmetric dichotomous noise with strengths $-Δ$ and $μΔ$, transitioning between these states at a rate $λ$. Starting from the Fokker-Planck~(FP) equation for the time-dependent probability distributions $P(v,-Δ,t)$ and $P(v,μΔ,t)$ of the particle's velocity $v$ at time $t$, moving under the influence of active forces $-Δ$ and $μΔ$ respectively, we analytically derive the steady-state velocity distribution function $P_s(v)$, explicitly dependent on $μ$. Also, we obtain a quadrature expression for the effective diffusion coefficient $D_e$ for the symmetric active force case~($μ=1$). For a given $Δ$ and $μ$, we show that $P_s(v)$ exhibits multiple transitions as $λ$ is varied. Subsequently, we numerically compute $P_s(v)$, the mean-squared velocity $\langle v^2\rangle(t)$, and the diffusion coefficient $D_e$ by solving the particle's equation of motion, all of which show excellent agreement with the analytical results in the steady-state. Finally, we examine the universal nature of the transitions in $P_s(v)$ by considering an alternative functional form of medium's viscosity that also capture the shear-thinning behavior. △ Less

Submitted 15 April, 2025; originally announced April 2025.

Comments: 20 Pages, 7 Figures, Accepted to Physics of Fluids

Journal ref: Physics of Fluids 37, 057114 (2025)

Two-Axis planar Hall magnetic field sensors with sub nanoTesla resolution

Authors: Proloy Taran Das, Hariharan Nhalil, Vladislav Mor, Moty Schultz, Nir Hasidim, Asaf Grosz, Lior Klein

Abstract: Planar Hall effect (PHE) magnetic sensors are attractive for various applications where the field resolution is required in the range of sub-nano Tesla or in Pico Tesla. Here we present a detailed noise study of the PHE sensors consisting of two or three intersecting ellipses. It can be used to measure two axes of the magnetic field in the sensor plane in particular along the two perpendicular eas… ▽ More Planar Hall effect (PHE) magnetic sensors are attractive for various applications where the field resolution is required in the range of sub-nano Tesla or in Pico Tesla. Here we present a detailed noise study of the PHE sensors consisting of two or three intersecting ellipses. It can be used to measure two axes of the magnetic field in the sensor plane in particular along the two perpendicular easy axes in the overlapping region for two intersecting ellipses and three easy axes at an angle of 60 degrees for three crossing ellipses. Thus, for each remanent magnetic state in the overlap area, the sensor can measure the vector component of the magnetic field perpendicular to the direction of the remanent magnetization. The two field components are measured with a field resolution less than 200 pT/sqrt(Hz) at 10 Hz and 350 pT/sqrt(Hz) at 1 Hz in the same region, while maintaining a similar size and noise level of a single-axis sensor. Furthermore, we discuss here the possible route for future improvement of the field resolution △ Less

Submitted 9 April, 2025; originally announced April 2025.

Comments: 4 pages, 4 figures

Journal ref: IEEE Transactions on Magnetics, vol. 60, no. 9, pp. 1-4, Sept. 2024, Art no. 4000404

Exchange-Biased multi-ring Planar Hall Magnetoresistive Sensors with nT resolution in Non-Shielded Environments

Authors: Jan Schmidtpeter, Proloy Taran Das, Yevhen Zabila, Conrad Schubert, Thomas Gundrum, Thomas Wondrak, Denys Makarov

Abstract: Planar Hall magnetoresistive sensors (PHMR) are promising candidates for various magnetic sensing applications due to their high sensitivity, low power consumption, and compatibility with integrated circuit technology. However, their performance is often limited by inherent noise sources, impacting their resolution and overall sensitivity. Here the effect of three bilayer structures NiFe(10 nm)/Ir… ▽ More Planar Hall magnetoresistive sensors (PHMR) are promising candidates for various magnetic sensing applications due to their high sensitivity, low power consumption, and compatibility with integrated circuit technology. However, their performance is often limited by inherent noise sources, impacting their resolution and overall sensitivity. Here the effect of three bilayer structures NiFe(10 nm)/IrMn(10 nm), NiFe(30 nm)/IrMn(10 nm), and NiFe(30 nm)/IrMn(20 nm) on noise levels is investigated at low-frequency (DC - 25 Hz). This study includes a detailed investigation on the optimization process and noise characteristics of multiring PHMR sensors, focusing on identifying and quantifying the dominant noise sources. The experimental measurements are complemented by a theoretical analysis of noise sources including thermal noise, 1/f noise, intermixing and environmental noise. The best magnetic resolution is observed for the NiFe(30 nm)/IrMn(10 nm) structure, which achieves a detectivity below 1.5 nT/sqrt(Hz) at 10 Hz in a non-shielded environment at room temperature. In addition, a substantial improvement in sensitivity is observed by annealing the sensors at 250 deg C for 1 hour. The findings of this study contribute to a deeper understanding of noise behavior in PHMR sensors, paving the way for developing strategies to improve their performance for demanding sensing applications at low frequencies. △ Less

Submitted 8 April, 2025; originally announced April 2025.

Comments: 4 pages, 5 figures

Journal ref: IEEE Magnetics Letters, vol. 15, pp. 1-5, 2024, Art no. 4100205

Integrating Density Functional Theory with Deep Neural Networks for Accurate Voltage Prediction in Alkali-Metal-Ion Battery Materials

Authors: Sk Mujaffar Hossain, Namitha Anna Koshi, Seung-Cheol Lee, G. P Das, Satadeep Bhattacharjee

Abstract: Accurate prediction of the voltage of battery materials plays a pivotal role in the advancement of energy storage technologies and the rational design of high-performance cathode materials. In this work, we present a deep neural network (DNN) model, built using PyTorch, to estimate the average voltage of cathode materials across Li-ion, Na-ion, and other alkali-metal-ion batteries. The model is tr… ▽ More Accurate prediction of the voltage of battery materials plays a pivotal role in the advancement of energy storage technologies and the rational design of high-performance cathode materials. In this work, we present a deep neural network (DNN) model, built using PyTorch, to estimate the average voltage of cathode materials across Li-ion, Na-ion, and other alkali-metal-ion batteries. The model is trained on an extensive dataset from the Materials Project, incorporating a wide range of specific structural, physical, chemical, electronic, thermodynamic, and battery descriptors, ensuring a comprehensive representation of material properties. Our model exhibits strong predictive performance, as corroborated by first-principles density functional theory (DFT) calculations. The close alignment between the DNN predictions and the DFT outcomes highlights the robustness and accuracy of our machine learning framework to effectively select and identify viable battery materials. Using this validated model, we successfully proposed novel Na-ion battery compositions, with their predicted behavior confirmed by rigorous computational assessment. By seamlessly integrating data-driven prediction with first-principles validation, this study presents an effective framework that significantly accelerates the discovery and optimization of advanced battery materials, contributing to the development of more reliable and efficient energy storage technologies. △ Less

Submitted 21 August, 2025; v1 submitted 17 March, 2025; originally announced March 2025.

Applications of the Quantum Phase Difference Estimation Algorithm to the Excitation Energies in Spin Systems on a NISQ Device

Authors: Boni Paul, Sudhindu Bikash Mandal, Kenji Sugisaki, B. P. Das

Abstract: The Quantum Phase Difference Estimation (QPDE) algorithm, as an extension of the Quantum Phase Estimation (QPE), is a quantum algorithm designed to compute the differences of two eigenvalues of a unitary operator by exploiting the quantum superposition of two eigenstates. Unlike QPE, QPDE is free of controlled-unitary operations, and is suitable for calculations on noisy intermediate-scale quantum… ▽ More The Quantum Phase Difference Estimation (QPDE) algorithm, as an extension of the Quantum Phase Estimation (QPE), is a quantum algorithm designed to compute the differences of two eigenvalues of a unitary operator by exploiting the quantum superposition of two eigenstates. Unlike QPE, QPDE is free of controlled-unitary operations, and is suitable for calculations on noisy intermediate-scale quantum (NISQ) devices. We present the implementation and verification of a novel early fault-tolerant QPDE algorithm for determining energy gaps across diverse spin system configurations using NISQ devices. The algorithm is applied to the systems described by two and three-spin Heisenberg Hamiltonians with different geometric arrangements and coupling strengths, including symmetric, asymmetric, spin-frustrated, and non-frustrated configurations. By leveraging the match gate-like structure of the time evolution operator of Heisenberg Hamiltonian, we achieve constant-depth quantum circuits suitable for NISQ hardware implementation. Our results on IBM quantum processors show remarkable accuracy ranging from 85\% to 93\%, demonstrating excellent agreement with classical calculations even in the presence of hardware noise. The methodology incorporates sophisticated quantum noise suppression techniques, including Pauli Twirling and Dynamical Decoupling, and employs an adaptive framework. Our findings demonstrate the practical viability of the QPDE algorithm for quantum many-body simulations on current NISQ hardware, establishing a robust framework for future applications. △ Less

Submitted 27 February, 2025; originally announced February 2025.

New Methods for Critical Analysis: Revealing the Simultaneous Existence of Universality Classes in Nontrivial Magnetic Systems

Authors: Harish Chandr Chauhan, Umesh C. Roy, Shovan Dan, A. Thamizhavel, Pintu Das

Abstract: In magnetic systems, the microscopic constituents exhibit power law behavior near the paramagnetic transition temperature, $T_C$. The critical exponents (CEs) associated with the physical quantities that demonstrate singular behavior at $T_C$ illustrate the critical behavior, specifically the range and type of exchange interactions emerging in magnetic systems. However, it is realized that the dev… ▽ More In magnetic systems, the microscopic constituents exhibit power law behavior near the paramagnetic transition temperature, $T_C$. The critical exponents (CEs) associated with the physical quantities that demonstrate singular behavior at $T_C$ illustrate the critical behavior, specifically the range and type of exchange interactions emerging in magnetic systems. However, it is realized that the developed methodologies may not yield accurate values of CEs, especially for magnetic systems with competing interactions, referred to as nontrivial magnetic systems. Currently, no comprehensive method effectively addresses the competing effects of the range of magnetic interactions among the constituent entities emerging in such systems. Additionally, there is no definitive explanation for CE values that do not belong to any single universality class. Here, we present new methodologies for critical analysis aimed at determining both the range of exchange interaction(s) and appropriate values of CEs. Using computational and experimental investigations, we analyze the magnetic behavior of trivial Ni and nontrivial Gd. Our findings demonstrate that (i) the critical behavior remains the same on either side of $T_C$, (ii) the critical behavior associated with local electron moments remains unaffected by the magnetic field, and (iii) in Gd, the critical role of competing interactions becomes evident: local electron moments follow a three-dimensional Ising-type short-range interaction, while itinerant electron moments exhibit a mean-field-type long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, which weakens under an external magnetic field due to the localization effect on itinerant electrons. △ Less

Submitted 11 May, 2025; v1 submitted 28 January, 2025; originally announced January 2025.

Hydrodynamic Equations for a system with translational and rotational dynamics

Authors: Akira Yoshimori, Shankar P. Das

Abstract: We obtain the equations of fluctuating hydrodynamics for many-particle systems whose microscopic units have both translational and rotational motion. The orientational dynamics of each element are studied in terms of the rotational Brownian motion of a corresponding fixed-length director ${\bf u}$. The time evolution of a set of collective densities $\{\hatψ\}$ is obtained as an exact representati… ▽ More We obtain the equations of fluctuating hydrodynamics for many-particle systems whose microscopic units have both translational and rotational motion. The orientational dynamics of each element are studied in terms of the rotational Brownian motion of a corresponding fixed-length director ${\bf u}$. The time evolution of a set of collective densities $\{\hatψ\}$ is obtained as an exact representation of the corresponding microscopic dynamics. For the Smoluchowski dynamics, noise in the Langevin equation for the director ${\bf u}$ is multiplicative. We obtain that the equation of motion for the collective number-density has two different forms, respectively, for the Ito and Stratonvich interpretation of the multiplicative noise in the ${\bf u}$-equation. Without the ${\bf u}$ variable, both reduce to the Standard Dean-Kawasaki form. Next, we average the microscopic equations for the collective densities $\{\hatψ\}$ (which are, at this stage, a collection of Dirac delta functions) over phase space variables and obtain a corresponding set of stochastic partial differential equations for the coarse-grained densities $\{ψ\}$ with smooth spatial and temporal dependence. The coarse-grained equations of motion for the collective densities $\{ψ\}$ constitute the fluctuating non-linear hydrodynamics for the fluid with both rotational and translational dynamics. From the stationary solution of the corresponding Fokker-Planck equation, we obtain a free energy functional ${\cal F}[ψ]$ and demonstrate the relation between the ${\cal F}[ψ]$s for different levels of the FNH descriptions with its corresponding set of $\{ψ\}$. △ Less

Submitted 16 January, 2025; originally announced January 2025.

Comments: 45 pages

Local Symmetry Breaking in Skyrmion-Hosting Centrosymmetric Hexagonal Compounds

Authors: Anupam K. Singh, Krishna K. Dubey, Parul Devi, Pritam Das, Martin Etter, Ola. G. Grendal, Catherine Dejoie, Andrew Fitch, Anatoliy Senyshyn, Seung-Cheol Lee, Satadeep Bhattacharjee, Sanjay Singh, Dhananjai Pandey

Abstract: Dzyaloshinskii-Moriya interaction (DMI) plays a crucial role in stabilizing the exotic topologically stable skyrmion spin textures in the noncentrosymmetric crystals. The recent discovery of biskyrmions and skyrmions in the globally centrosymmetric crystals has raised debate about the role of the DMI in causing the spin textures, since DMI vanishes in such crystal structures. Theoretical studies,… ▽ More Dzyaloshinskii-Moriya interaction (DMI) plays a crucial role in stabilizing the exotic topologically stable skyrmion spin textures in the noncentrosymmetric crystals. The recent discovery of biskyrmions and skyrmions in the globally centrosymmetric crystals has raised debate about the role of the DMI in causing the spin textures, since DMI vanishes in such crystal structures. Theoretical studies, on the other hand, suggest non-vanishing DMI even if there is local inversion symmetry breaking in an otherwise globally centrosymmetric crystal structure. Motivated by such theoretical predictions, we present here the results of a systematic crystal structure study of two skyrmion-hosting Ni2In-type centrosymmetric hexagonal compounds, MnNiGa and MnPtGa, using the atomic pair distribution function (PDF) technique. Our result provides information about structural correlations in the short-range (SR), medium-range (MR) and long-range (LR) regimes simultaneously. The analysis of the experimental PDFs, obtained from high flux, high energy, and high Q synchrotron x-ray powder diffraction patterns, reveals that the local SR structure of both MnNiGa and MnPtGa compounds corresponds to the noncentrosymmetric trigonal space group P3m1, while the structure in the MR+LR regimes remains hexagonal in the centrosymmetric P63/mmc space group. These findings are also supported by theoretical DFT calculations. Our results, in conjunction with the previous theoretical predictions, provide a rationale for the genesis of skyrmions in centrosymmetric materials in terms of non-vanishing DMI due to local inversion symmetry breaking. We believe that our findings would encourage a systematic search of skyrmionic textures and other topological phenomena in a vast family of centrosymmetric materials. △ Less

Submitted 5 December, 2025; v1 submitted 12 December, 2024; originally announced December 2024.

Inverse Superconductor-Insulator Transition in Weakly Monitored Josephson Junction Arrays

Authors: Purnendu Das, Sumilan Banerjee

Abstract: Control and manipulation of quantum states by measurements and bath engineering in open quantum systems have emerged as new paradigms in many-body physics. Here, taking a prototypical example of Josephson junction arrays (JJAs), we show how repetitive monitoring through continuous weak measurements and feedback can transform an insulating state in these systems to a superconductor and vice versa.… ▽ More Control and manipulation of quantum states by measurements and bath engineering in open quantum systems have emerged as new paradigms in many-body physics. Here, taking a prototypical example of Josephson junction arrays (JJAs), we show how repetitive monitoring through continuous weak measurements and feedback can transform an insulating state in these systems to a superconductor and vice versa. We show that, even in the absence of any external thermal bath, the monitoring leads to a long-time steady state characterized by an effective `quantum' temperature in a suitably defined semiclassical limit. However, we show that the quantum dissipation due to monitoring has fundamental differences with equilibrium quantum and/or thermal dissipation in the well-studied case of JJAs in contact with an Ohmic bath. In particular, using a variational approximation, and by considering various limiting cases, we demonstrate that this difference can give rise to re-entrant steady-state phase transitions, resulting in unusual inverse transition from an effective low-temperature insulating normal state to superconducting state at intermediate temperature. Our work emphasizes the role of quantum feedback, that acts as an additional knob to control the effective temperature of non-equilibrium steady state leading to a phase diagram, not explored in earlier works on monitored and open quantum systems. △ Less

Submitted 22 March, 2025; v1 submitted 5 December, 2024; originally announced December 2024.

Comments: 7+13 pages, 2+1 figures

Journal ref: Phys. Rev. B 112, L180503 (2025)

Enhancement of spin Hall angle by an order of magnitude via Cu intercalation in MoS$_2$/CoFeB heterostructures

Authors: Abhisek Mishra, Pritam Das, Rupalipriyadarsini Chhatoi, Soubhagya Dash, Shubhransu Sahoo, Kshitij Singh Rathore, Pil-Ryung Cha, Seung-Cheol Lee, Satadeep Bhattacharjee, Subhankar Bedanta

Abstract: Transition metal dichalcogenides (TMDs) are a novel class of quantum materials with significant potential in spintronics, optoelectronics, valleytronics, and opto-valleytronics. TMDs exhibit strong spin-orbit coupling, enabling efficient spin-charge interconversion, which makes them ideal candidates for spin-orbit torque-driven spintronic devices. In this study, we investigated the spin-to-charge… ▽ More Transition metal dichalcogenides (TMDs) are a novel class of quantum materials with significant potential in spintronics, optoelectronics, valleytronics, and opto-valleytronics. TMDs exhibit strong spin-orbit coupling, enabling efficient spin-charge interconversion, which makes them ideal candidates for spin-orbit torque-driven spintronic devices. In this study, we investigated the spin-to-charge conversion through ferromagnetic resonance in MoS$_2$/Cu/CoFeB heterostructures with varying Cu spacer thicknesses. The conversion efficiency, quantified by the spin Hall angle, was enhanced by an order of magnitude due to Cu intercalation. Magneto-optic Kerr effect microscopy confirmed that Cu did not significantly modify the magnetic domains, indicating its effectiveness in decoupling MoS$_2$ from CoFeB. This decoupling preserves the spin-orbit coupling (SOC) of MoS$_2$ by mitigating the exchange interaction with CoFeB, as proximity to localized magnetization can alter the electronic structure and SOC. First-principles calculations revealed that Cu intercalation notably enhances the spin Berry curvature and spin Hall conductivity, contributing to the increased spin Hall angle. This study demonstrates that interface engineering of ferromagnet/TMD-based heterostructures can achieve higher spin-to-charge conversion efficiencies, paving the way for advancements in spintronic applications. △ Less

Submitted 1 December, 2025; v1 submitted 27 November, 2024; originally announced November 2024.

Glucose Sensing Using Pristine and Co-doped Hematite Fiber-Optic sensors: Experimental and DFT Analysis

Authors: Namrata Pattanayak, Preeti Das, Mihir Ranjan Sahoo, Padmalochan Panda, Monalisa Pradhan, Kalpataru Pradhan, Reshma Nayak, Sumanta Kumar Patnaik, Sukanta Kumar Tripathy

Abstract: Glucose monitoring plays a critical role in managing diabetes, one of the most prevalent diseases globally. The development of fast-responsive, cost-effective, and biocompatible glucose sensors is essential for improving patient care. In this study, a comparative analysis is conducted between pristine and Co-doped hematite samples, synthesized via the hydrothermal method, to evaluate their structu… ▽ More Glucose monitoring plays a critical role in managing diabetes, one of the most prevalent diseases globally. The development of fast-responsive, cost-effective, and biocompatible glucose sensors is essential for improving patient care. In this study, a comparative analysis is conducted between pristine and Co-doped hematite samples, synthesized via the hydrothermal method, to evaluate their structural, morphological, and optical properties. The glucose sensing performance of both samples is assessed using a fiber-optic evanescent wave (FOEW) setup. While the sensitivity remains comparable for both pristine and Co-doped hematite, a reduction in the Limit of Detection (LoD) is observed in the Co-doped sample, suggesting enhanced interactions with glucose molecules at the surface. To gain further insights into the glucose adsorption mechanisms, Density Functional Theory (DFT) calculations are performed, revealing key details regarding charge transfer, electronic delocalization, and glucose binding on the hematite surfaces. These findings highlight the potential of Co-doped hematite for advanced glucose sensing applications, offering a valuable synergy between experimental and theoretical approaches for further exploration in biosensing technologies. △ Less

Submitted 9 November, 2024; originally announced November 2024.

Journal ref: Langmuir 2025, 41, 8866-8875

Linear non-saturating magnetoresistance and superconductivity in epitaxial thin films of YbSb$_{2}$

Authors: Rudra Dhara, Pritam Das, Sulagna Datta, Nilesh Kulkarni, Biswarup Satpati, Pratap Raychaudhuri, Shouvik Chatterjee

Abstract: Rare-earth diantimonides display intriguing ground states often associated with structural order, which can be manipulated in thin film geometries. In this study, we report epitaxial synthesis of one such compound, YbSb$_{2}$, on III-V substrates using molecular-beam epitaxy. The synthesized thin films exhibit large, non-saturating, linear magnetoresistance across a wide magnetic field range. Addi… ▽ More Rare-earth diantimonides display intriguing ground states often associated with structural order, which can be manipulated in thin film geometries. In this study, we report epitaxial synthesis of one such compound, YbSb$_{2}$, on III-V substrates using molecular-beam epitaxy. The synthesized thin films exhibit large, non-saturating, linear magnetoresistance across a wide magnetic field range. Additionally, they demonstrate superconducting properties, with a critical temperature of $\approx$ 1.025 K and a critical field of $\approx$ 83.85 Oe, consistent with the reports in bulk single crystals. While YbSb$_{2}$ has been classified as a Type-I superconductor in its bulk form, our findings provide evidence of a mixed state in the epitaxial thin films. This work paves the way for controlling the electronic ground state in this class of materials through thin film engineering. △ Less

Submitted 7 November, 2024; originally announced November 2024.

Comments: 8 pages, 6 figures

Journal ref: Phys. Rev. Materials 9, 034801 (2025)

Domain Growth Kinetics in Active Binary Mixtures

Authors: Sayantan Mondal, Prasenjit Das

Abstract: We study motility-induced phase separation (MIPS) in symmetric and asymmetric active binary mixtures. We start with the coarse-grained run-and-tumble bacterial model that provides evolution equations for the density fields $ρ_i(\vec r, t)$. Next, we study the phase separation dynamics by solving the evolution equations using the Euler discretization technique. We characterize the morphology of dom… ▽ More We study motility-induced phase separation (MIPS) in symmetric and asymmetric active binary mixtures. We start with the coarse-grained run-and-tumble bacterial model that provides evolution equations for the density fields $ρ_i(\vec r, t)$. Next, we study the phase separation dynamics by solving the evolution equations using the Euler discretization technique. We characterize the morphology of domains by calculating the equal-time correlation function $C(r, t)$ and the structure factor $S(k, t)$, both of which show dynamical scaling. The form of the scaling functions depends on the mixture composition and the relative activity of the species, $Δ$. For $k\rightarrow\infty$, $S(k, t)$ follows Porod's law: $S(k, t)\sim k^{-(d+1)}$ and the average domain size $L(t)$ shows a diffusive growth as $L(t)\sim t^{1/3}$ for all mixtures. △ Less

Submitted 1 October, 2024; originally announced October 2024.

Comments: 19 Pages,11 Figures,

Report number: J. Chem. Phys. 161, 134902 (2024)

A compact inertial nano-positioner operating at cryogenic temperatures

Authors: Pritam Das, Sulagna Dutta, Krishna K. S., John Jesudasan, Pratap Raychaudhuri

Abstract: Nano-positioning plays a very important role in applications such as scanning probe microscopy and optics. We report the development of a compact inertial nanopositioner along with fully computer interfaced electronics operating down to 2 K, and its use in our fully automated needle-anvil type Point Contact Andreev Reflection (PCAR) apparatus. We also present the fully automated operational proced… ▽ More Nano-positioning plays a very important role in applications such as scanning probe microscopy and optics. We report the development of a compact inertial nanopositioner along with fully computer interfaced electronics operating down to 2 K, and its use in our fully automated needle-anvil type Point Contact Andreev Reflection (PCAR) apparatus. We also present the fully automated operational procedures using LabVIEW interface with our home-built electronics. The point contact spectroscopy probe has been successfully used to perform PCAR measurements on elemental superconductors at low temperatures. The small footprint of our nano-positioner makes it ideally suited for incorporation in low temperature scanning probe microscopes and makes this design versatile for various research and industrial purposes. △ Less

Submitted 24 September, 2024; v1 submitted 23 September, 2024; originally announced September 2024.

Journal ref: Rev. Sci. Instrum. 95, 113708 (2024

First-principles study of structural, electronic and optical properties of non-toxic RbBaX$_3$ (X = F, Cl, Br, I) perovskites under hydrostatic pressure

Authors: Pranti Saha, In Jun Park, Protik Das, Fariborz Kargar

Abstract: We have investigated the structural, mechanical, electronic and optical properties of Rb-based cubic perovskite RbBaX$_3$ (X = F, Cl, Br, I) under hydrostatic pressure, using first-principle density functional theory (DFT). All RbBaX$_3$ perovskites exhibit thermodynamic and mechanical stability at ambient pressure. RbBaF$_3$ remains structurally stable across all examined pressures, while RbBaCl… ▽ More We have investigated the structural, mechanical, electronic and optical properties of Rb-based cubic perovskite RbBaX$_3$ (X = F, Cl, Br, I) under hydrostatic pressure, using first-principle density functional theory (DFT). All RbBaX$_3$ perovskites exhibit thermodynamic and mechanical stability at ambient pressure. RbBaF$_3$ remains structurally stable across all examined pressures, while RbBaCl$_3$, RbBaBr$_3$, and RbBaI$_3$ maintain mechanical stability up to 60, 60, and 40 GPa, respectively. These materials are ductile even at elevated pressure. RbBaF$_3$ has a direct bandgap of 4.80 eV while other compositions exhibit indirect band gaps of 4.37, 3.73, and 3.24 eV with halide atoms of Cl, Br, and I, respectively. Under elevated hydrostatic pressure, only RbBaCl$_3$ and RbBaI$_3$ exhibit an indirect-to direct band transition while others preserve their nature of band gap. Our results show that spin-orbit coupling significantly affects only the valance bands of larger-sized halides (Cl, Br, I). With hybrid functional (HSE) correction, the band gaps of these four materials increase to 6.7, 5.6, 4.8 and 4.4 eV, respectively, but the nature of direct/indirect band transition remains unchanged. Orbital-decomposed partial density of states calculation reveals that the halogen p-orbitals dominate the valence band near the Fermi level, while Rb 5s-orbital affects the conduction band minima the most. Investigation of the optical properties reveals wide-band absorption, low electron loss, moderate reflectivity and lower refractive index in the UV to deep-UV range. The strength and range of absorption increases significantly with hydrostatic pressure, suggesting that RbBaX$_3$ perovskites are promising candidates for tunable UV-absorbing optoelectronic devices. △ Less

Submitted 14 September, 2024; originally announced September 2024.

Comments: 14 pages, 13 figures

Insights from the exact analytical solution of periodically driven transverse field Ising chain

Authors: Pritam Das, Anirban Dutta

Abstract: We derive an exact analytical expression at stroboscopic intervals for the time-dependent wave function of a class of integrable quantum many-body systems, driven by the periodic delta-kick protocol. To investigate long-time dynamics, we use the wave function to obtain an exact analytical expression for the expectation values of the defect density, magnetization, residual energy, fidelity, and the… ▽ More We derive an exact analytical expression at stroboscopic intervals for the time-dependent wave function of a class of integrable quantum many-body systems, driven by the periodic delta-kick protocol. To investigate long-time dynamics, we use the wave function to obtain an exact analytical expression for the expectation values of the defect density, magnetization, residual energy, fidelity, and the correlation function after the $n$th drive cycle. Periodically driven integrable closed quantum systems absorb energy, and the long-time universal dynamics are described by the periodic generalized Gibbs ensemble (GGE). We demonstrate that the expectation values of all observables are divided into two parts: one highly oscillatory term that depends on the drive cycle n, and the rest of the terms are independent of it. Typically, the $n$-independent part constitutes the saturation at large n and periodic GGE. The contribution from the highly oscillatory term vanishes in large $n$. We also generalize our formalism to include square pulse and sinusoidal driving protocols. △ Less

Submitted 29 January, 2025; v1 submitted 13 September, 2024; originally announced September 2024.

Comments: 16 pages, 31 figures

Journal ref: Phys. Rev. B 111, 045159 (2025)

Tuning the Planarity of an Aromatic Thianthrene-Based Molecule on Au(111)

Authors: Kwan Ho Au-Yeung, Suchetana Sarkar, Sattwick Haldar, Pranjit Das, Tim Kühne, Dmitry A. Ryndyk, Preeti Bhauriyal, Stefan Kaskel, Thomas Heine, Gianaurelio Cuniberti, Andreas Schneemann, Francesca Moresco

Abstract: Non-planar aromatic molecules are interesting systems for organic electronics and optoelectronics applications due to their high stability and electronic properties. By using scanning tunneling microscopy and spectroscopy, we investigated thianthrene-based molecules adsorbed on Au(111), which are non-planar in the gas phase and the bulk solid state. Varying the molecular coverage leads to the form… ▽ More Non-planar aromatic molecules are interesting systems for organic electronics and optoelectronics applications due to their high stability and electronic properties. By using scanning tunneling microscopy and spectroscopy, we investigated thianthrene-based molecules adsorbed on Au(111), which are non-planar in the gas phase and the bulk solid state. Varying the molecular coverage leads to the formation of two different kinds of self-assembled structures: close-packed islands and quasi one-dimensional chains. We found that the molecules are non-planar within the close-packed islands, while the configuration is planar in the molecular chain and for single adsorbed molecules. Using vertical tip manipulation to isolate a molecule from the island, we demonstrate the conversion of a non-planar molecule to its planar configuration. We discuss the two different geometries and their electronic properties with the support of density functional theory calculations. △ Less

Submitted 9 September, 2024; originally announced September 2024.

Spin dynamics in itinerant antiferromagnet SrCr$_2$As$_2$

Authors: Zhenhua Ning, Pinaki Das, Y. Lee, N. S. Sangeetha, Douglas L. Abernathy, D. C. Johnston, R. J. McQueeney, D. Vaknin, Liqin Ke

Abstract: SrCr$_2$As$_2$ is an itinerant antiferromagnet in the same structural family as the SrFe$_2$As$_2$ high-temperature superconductors. We report our calculations of exchange-coupling parameters $J_{ij}$ for SrCr$_2$As$_2$ using a static linear-response method based on first-principles electronic-structure calculations. We find that the dominant nearest-neighbor exchange coupling $J_{\rm{1}} > 0$ is… ▽ More SrCr$_2$As$_2$ is an itinerant antiferromagnet in the same structural family as the SrFe$_2$As$_2$ high-temperature superconductors. We report our calculations of exchange-coupling parameters $J_{ij}$ for SrCr$_2$As$_2$ using a static linear-response method based on first-principles electronic-structure calculations. We find that the dominant nearest-neighbor exchange coupling $J_{\rm{1}} > 0$ is antiferromagnetic whereas the next-nearest-neighbor interaction $J_{\rm{2}} < 0$ is ferromagnetic with $J_{\rm{2}}$/$J_{\rm{1}}$~=~$-0.68$, reinforcing the checkerboard in-plane magnetic structure. Thus, unlike other transition-metal arsenides based on Mn, Fe, or Co, we find no competing magnetic interactions in SrCr$_2$As$_2$, which aligns with experimental findings. Moreover, the orbital resolution of exchange interactions shows that $J_1$ and $J_2$ are dominated by direct exchange mediated by the Cr $d$ orbitals. To validate the calculations we conduct inelastic neutron-scattering measurements on powder samples that show steeply dispersive magnetic excitations arising from the magnetic $Γ$ points and persisting up to energies of at least 175 meV. The spin-wave spectra are then modeled using the Heisenberg Hamiltonian with the theoretically-calculated exchange couplings. The calculated neutron-scattering spectra are in good agreement with the experimental data. △ Less

Submitted 25 April, 2025; v1 submitted 10 August, 2024; originally announced August 2024.

Comments: 9 pages, 9 figures

Journal ref: Phys. Rev. B 111, 134438 (2025)

Origin of unexpected weak Gilbert damping in the LSMO/Pt bilayer system

Authors: Pritam Das, Pushpendra Gupta, Seung-Cheol Lee, Subhankar Bedanta, Satadeep Bhattacharjee

Abstract: This study presents a first-principles and semiclassical analysis of the puzzling observation that a La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) thin film exhibits larger Gilbert damping than an LSMO/Pt bilayer, contrary to conventional spin-pumping expectations. Density functional theory with Wannier interpolation yields an intrinsic damping of… ▽ More This study presents a first-principles and semiclassical analysis of the puzzling observation that a La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) thin film exhibits larger Gilbert damping than an LSMO/Pt bilayer, contrary to conventional spin-pumping expectations. Density functional theory with Wannier interpolation yields an intrinsic damping of $α_{\mathrm{int}}^{\mathrm{LSMO}}\!\approx\!1.4\times10^{-3}$, supporting an extrinsic origin of the high experimental value. Guided by the self-induced inverse spin Hall effect (ISHE) demonstrated in LSMO [Gupta et al., Phys.Rev. B 109, 014437 (2024)], we argue that the large spin Hall angle $|θ_{\mathrm{SH}}|\simeq 0.093$ and low longitudinal conductivity of LSMO enable an efficient conversion of spin current to charge current boosting the effective damping. In the LSMO/Pt heterostructure the Pt cap shunts the charge current, raising $σ_{xx}$ and reducing the interfacial $|θ_{\mathrm{SH}}|$ to~0.007. A Valet-Fert analysis for layer-resolved ab-initio spin accumulation gives the Pt spin-diffusion length and a non-negligible antidamping SOT coefficient, qualitatively accounting for the observed damping reduction under current bias. The seemingly anomalous damping hierarchy is thus reconciled without invoking additional interfacial mechanisms. The distinct length scales governing spin-pumping normalization, namely, the short absorption depth relevant to self-pumping in a single LSMO film versus the full magnetic thickness applicable to an LSMO/Pt bilayer, are crucial in this context. This observation suggests a practical design strategy: by simultaneously tuning the spin Hall-to-longitudinal conductivity ratio and the spin-diffusion length, one can engineer heterostructures with minimized magnetic losses for spin-orbitronics applications. △ Less

Submitted 19 August, 2025; v1 submitted 2 August, 2024; originally announced August 2024.

Emergent Moiré fringes in direct-grown quasicrystal

Authors: Jingwei Li, Kejie Bao, Honglin Sun, Xingxu Yan, Ting Huang, Qicheng Zhang, Yaoqiang Zhou, Zhenjing Liu, Paul Masih Das, Jiawen You, Jiong Zhao, Jianbin Xu, Xiaoqing Pan, Yongli Mi, Junyi Zhu, Zhaoli Gao

Abstract: Quasicrystals represent a category of rarely structured solids that challenge traditional periodicity in crystal materials. Recent advancements in the synthesis of two-dimensional (2D) van der Waals materials have paved the way for exploring the unique physical properties of these systems. Here, we report on the synthesis of 2D quasicrystals featuring 30° alternating twist angles between multiple… ▽ More Quasicrystals represent a category of rarely structured solids that challenge traditional periodicity in crystal materials. Recent advancements in the synthesis of two-dimensional (2D) van der Waals materials have paved the way for exploring the unique physical properties of these systems. Here, we report on the synthesis of 2D quasicrystals featuring 30° alternating twist angles between multiple graphene layers, using chemical vapor deposition (CVD). Strikingly, we observed periodic Moiré patterns in the quasicrystal, a finding that has not been previously reported in traditional alloy-based quasicrystals. The Moiré periodicity, varying with the parity of the constituent layers, aligns with the theoretical predictions that suggest a stress cancellation mechanism in force. The emergence of Moiré fringes is attributed to the spontaneous mismatched lattice constant in the oriented graphene layers, proving the existence of atomic relaxation. This phenomenon, which has been largely understudied in graphene systems with large twist angles, has now been validated through our use of scanning transmission electron microscopy (STEM). Our CVD-grown Moiré quasicrystal provides an ideal platform for exploring the unusual physical properties that arise from Moiré periodicity within quasicrystals. △ Less

Submitted 11 June, 2024; originally announced June 2024.

Electrically Tunable Magnetoconductance of Close-Packed CVD Bilayer Graphene Layer Stacking Walls

Authors: Qicheng Zhang, Sheng Wang, Zhaoli Gao, Sebastian Hurtado-Parra, Joel Berry, Zachariah Addison, Paul Masih Das, William M. Parkin, Marija Drndic, James M. Kikkawa, Feng Wang, Eugene J. Mele, A. T. Charlie Johnson, Zhengtang Luo

Abstract: Quantum valley Hall (QVH) domain wall states are a new class of one-dimensional (1D) one-way conductors that are topologically protected in the absence of valley mixing. Development beyond a single QVH channel raises important new questions as to how QVH channels in close spatial proximity interact with each other, and how that interaction may be controlled. Scalable epitaxial bilayer graphene syn… ▽ More Quantum valley Hall (QVH) domain wall states are a new class of one-dimensional (1D) one-way conductors that are topologically protected in the absence of valley mixing. Development beyond a single QVH channel raises important new questions as to how QVH channels in close spatial proximity interact with each other, and how that interaction may be controlled. Scalable epitaxial bilayer graphene synthesis produces layer stacking wall (LSW) bundles, where QVH channels are bound, providing an excellent platform to study QVH channel interactions. Here we show that distinct strain sources lead to the formation of both well-separated LSWs and close packed LSW bundles. Comparative studies of electronic transport in these two regimes reveal that close-packed LSW bundles support electrically tunable magnetoconductance. The coexistence of different strain sources offers a potential pathway to realize scalable quantum transport platform based on LSWs where electrically tunability enables programmable functionality. △ Less

Submitted 10 June, 2024; originally announced June 2024.

Electron Confinement-Induced Plasmonic Breakdown in Metals

Authors: Prasanna Das, Sourav Rudra, Dheemahi Rao, Souvik Banerjee, Ashalatha Indiradevi Kamalasanan Pillai, Magnus Garbrecht, Alexandra Boltasseva, Igor V. Bondarev, Vladimir M. Shalaev, Bivas Saha

Abstract: Plasmon resonance in metals represents the collective oscillation of the free electron gas density and enables enhanced light-matter interactions in nanoscale dimensions. Traditionally, the classical Drude model describes the plasmonic excitation, wherein the plasma frequency exhibits no spatial dispersion. Here, we show conclusive experimental evidence of the breakdown of the plasmon resonance an… ▽ More Plasmon resonance in metals represents the collective oscillation of the free electron gas density and enables enhanced light-matter interactions in nanoscale dimensions. Traditionally, the classical Drude model describes the plasmonic excitation, wherein the plasma frequency exhibits no spatial dispersion. Here, we show conclusive experimental evidence of the breakdown of the plasmon resonance and a consequent photonic metal-insulator transition in an ultrathin archetypal refractory plasmonic material, hafnium nitride (HfN). Epitaxial HfN thick films exhibit a low-loss and high-quality Drude-like plasmon resonance in the visible spectral range. However, as the film thickness is reduced to nanoscale dimensions, the Coulomb interaction among electrons increases due to the electron confinement, leading to the spatial dispersion of the plasma frequency. Importantly, with the further decrease in thickness, electrons lose their ability to shield the incident electric field, turning the medium into a dielectric. The breakdown of the plasmon resonance in epitaxial ultrathin metals could be useful for fundamental physics studies in transdimensional regimes and novel photonic device applications. △ Less

Submitted 5 June, 2024; originally announced June 2024.

Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

Authors: Carlos G. Torres-Castanedo, Dominic P. Goronzy, Thang Pham, Anthony McFadden, Nicholas Materise, Paul Masih Das, Matthew Cheng, Dmitry Lebedev, Stephanie M. Ribet, Mitchell J. Walker, David A. Garcia-Wetten, Cameron J. Kopas, Jayss Marshall, Ella Lachman, Nikolay Zhelev, James A. Sauls, Joshua Y. Mutus, Corey Rae H. McRae, Vinayak P. Dravid, Michael J. Bedzyk, Mark C. Hersam

Abstract: Superconducting Nb thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride-based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potenti… ▽ More Superconducting Nb thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride-based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, we present comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments. In particular, secondary-ion mass spectrometry, X-ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb2O5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power-independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two-level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices. △ Less

Submitted 5 April, 2024; originally announced April 2024.

Virial Equation of State for a Granular System

Authors: Subhanker Howlader, Prasenjit Das

Abstract: The equation of state for an ideal gas is simple, which is $P=nk_{\rm B}T$. In the case of imperfect gases where mutual interactions among the constituents are important, pressure $P$ can be expressed as the series expansion of density $n$ with appropriate coefficients, known as virial coefficients $B_m$. In this paper, we have obtained the first four virial coefficients for a model interaction po… ▽ More The equation of state for an ideal gas is simple, which is $P=nk_{\rm B}T$. In the case of imperfect gases where mutual interactions among the constituents are important, pressure $P$ can be expressed as the series expansion of density $n$ with appropriate coefficients, known as virial coefficients $B_m$. In this paper, we have obtained the first four virial coefficients for a model interaction potential $Φ(r)$ using multidimensional Monte-Carlo integration and importance sampling methods. Next, we perform molecular dynamics simulations with the same $Φ(r)$ for a many-particle system to obtain $P$ as a function of $T$ and $n$. We compare our numerical data with the virial equation of state. △ Less

Submitted 16 March, 2024; v1 submitted 26 February, 2024; originally announced February 2024.

Comments: 15 Pages, 7 Figures

Journal ref: Eur. Phys. J. E 47, 20 (2024)

Quantum Linear Magnetoresistance and Fermi Liquid Behavior in Kagome Metal Ni3In2S2

Authors: P. Das, P. Saha, M. Singh, P. Kumar, S. Patnaik

Abstract: Kagome metals gain attention as they manifest a spectrum of quantum phenomena, including superconductivity, charge order, frustrated magnetism, and intertwined correlated states of condensed matter. With regard to electronic band structure, several of the them exhibit non-trivial topological characteristics. Here, we present a thorough investigation on the growth and the physical properties of sin… ▽ More Kagome metals gain attention as they manifest a spectrum of quantum phenomena, including superconductivity, charge order, frustrated magnetism, and intertwined correlated states of condensed matter. With regard to electronic band structure, several of the them exhibit non-trivial topological characteristics. Here, we present a thorough investigation on the growth and the physical properties of single crystals of Ni3In2S2 which is established to be a Dirac nodal line Kagome metal. Extensive characterization is attained through temperature and field-dependent resistivity, angle-dependent magnetoresistance and specific heat measurements. In most metals, the Fermi liquid behaviour is mostly restricted to a narrow range of temperature. In Ni3In2S2, this characteristic feature has been observed for an extensive temperature range of 82 K. This is attributed to the strong electron-electron correlation in the material. Specific heat measurements reveal a high Kadowaki-Woods ratio which is in good agreement with strongly correlated systems. Almost linear positive magnetoresistance follows the conventional Kohler scaling which depicts the applicability of semi-classical theories. The angle-dependent magneto-resistance been explained using the Voigt-Thomson formula. Furthermore, de-Haas van Alphen oscillations are observed in magnetization vs. magnetic field measurement which shed light on the topological features in the Shandite Ni3In2S2. △ Less

Submitted 15 February, 2024; originally announced February 2024.

A Hybrid Machine Learning Framework for Predicting Hydrogen Storage Capacities in Metal Hydrides: Unsupervised Feature Learning with Deep Neural Networks

Authors: Satadeep Bhattacharjee, Pritam Das, Swetarekha Ram, Seung-Cheol Lee

Abstract: In this study, we present a sophisticated hybrid machine-learning framework that significantly improves the accuracy of predicting hydrogen storage capacities in metal hydrides. This is a critical challenge due to the scarcity of experimental data and the complexity of high-dimensional feature spaces. Our approach employs the power of unsupervised learning through the use of a state-of-the-art aut… ▽ More In this study, we present a sophisticated hybrid machine-learning framework that significantly improves the accuracy of predicting hydrogen storage capacities in metal hydrides. This is a critical challenge due to the scarcity of experimental data and the complexity of high-dimensional feature spaces. Our approach employs the power of unsupervised learning through the use of a state-of-the-art autoencoder. This autoencoder is trained on elemental descriptors obtained from Mendeleev software, enabling the extraction of a meaningful and lower dimensional latent space from the input data. This latent representation serves as the basis for our deep multi-layer perceptron (MLP) model, which consists of five layers and shows good precision in predicting hydrogen storage capacities. Furthermore, our results show very good agreement with the results of density functional theory (DFT). In addition to addressing the limitations caused by limited and unevenly distributed data in the field of hydrogen storage materials, we also focus on discovering new materials that show promising opportunities for hydrogen storage. These materials were identified using both feature-based approaches and predictions generated by a large language model. Finally, our investigation into the effectiveness of transferring weights from the autoencoder to the MLP, in addition to the latent features, suggests that while this strategy slightly improves model performance indicated by a slightly higher R$^2$ value and lower RMSE, it emphasizes the intricate challenge of adapting pre-trained weights for specific supervised tasks. △ Less

Submitted 28 August, 2024; v1 submitted 30 January, 2024; originally announced January 2024.

Endless Dirac nodal lines and high mobility in kagome semimetal Ni3In2Se2 single crystal

Authors: Sanand Kumar Pradhan, Sharadnarayan Pradhan, Priyanath Mal, P. Rambabu, Archana Lakhani, Bipul Das, Bheema Lingam Chittari, G. R. Turpu, Pradip Das

Abstract: Kagome-lattice crystal is crucial in quantum materials research, exhibiting unique transport properties due to its rich band structure and the presence of nodal lines and rings. Here, we investigate the electronic transport properties and perform first-principles calculations for Ni$_{3}$In$_{2}$Se$_{2}$ kagome topological semimetal. First-principle calculations indicate six endless Dirac nodal li… ▽ More Kagome-lattice crystal is crucial in quantum materials research, exhibiting unique transport properties due to its rich band structure and the presence of nodal lines and rings. Here, we investigate the electronic transport properties and perform first-principles calculations for Ni$_{3}$In$_{2}$Se$_{2}$ kagome topological semimetal. First-principle calculations indicate six endless Dirac nodal lines and two nodal rings with a $π$-Berry phase in the Ni$_{3}$In$_{2}$Se$_{2}$ compound. The temperature-dependent resistivity is dominated by two scattering mechanisms: $s$-$d$ interband scattering occurs below 50 K, while electron-phonon ($e$-$p$) scattering is observed above 50 K. The magnetoresistance (MR) curve aligns with the theory of extended Kohler's rule, suggesting multiple scattering origins and temperature-dependent carrier densities. A maximum MR of 120\% at 2 K and 9 T, with a maximum estimated mobility of approximately 3000 cm$^{2}$V$^{-1}$s$^{-1}$ are observed. The Ni atom's hole-like d$_{x^{2}-y^{2} }$ and electron-like d$_{z^{2}}$ orbitals exhibit peaks and valleys, forming a local indirect-type band gap near the Fermi level (E$_{F}$). This configuration enhances the motion of electrons and holes, resulting in high mobility and relatively high magnetoresistance. △ Less

Submitted 6 January, 2024; originally announced January 2024.