Showing 1–50 of 327 results for author: Mishra, S

Probing bulk superconductivity in centrosymmetric Te-doped PtBi$_2$ single crystals

Authors: Kilian Srowik, Pablo Pedrazzini, Soumen Ash, Oksana Kvitnitskaya, Andrii Kuibarov, Susmita Changdar, Oleksandr Suvorov, Volodymyr Bezguba, Alexander Kordyuk, Rafał Kurleto, Dawid Wutke, Reza Firouzmandi, Robert Kluge, Swarnamayee Mishra, Alexander Mistonov, Saicharan Aswartham, Jochen Geck, Sergey Borisenko, Laura T. Corredor, Bernd Büchner

Abstract: The Weyl semimetal $γ$-PtBi$_2$ has been shown to be one of the most promising novel materials, recently proposed as a topological i-wave superconductor. A crucial requirement for observing this physics is the absence of inversion symmetry in its trigonal $P31m$ crystal structure. Centrosymmetry has been reported to be readily restored in the $P\overline{3}m1$ structure upon electron doping, parti… ▽ More The Weyl semimetal $γ$-PtBi$_2$ has been shown to be one of the most promising novel materials, recently proposed as a topological i-wave superconductor. A crucial requirement for observing this physics is the absence of inversion symmetry in its trigonal $P31m$ crystal structure. Centrosymmetry has been reported to be readily restored in the $P\overline{3}m1$ structure upon electron doping, partially substituting Bi with as little as 2% Te. In this work, we synthesized Te-doped PtBi$_{2-x}$Te$_{x}$ samples and thoroughly investigated the bulk superconductivity of selected single crystals with nominal composition PtBi$_{1.96}$Te$_{0.04}$, exhibiting the highest superconducting volume fraction of $\sim100$%. Single crystal XRD measurements confirm the centrosymmetric $P\overline{3}m1$ structure in our samples, whereas bulk superconductivity with a critical temperature of $T_\mathrm{c} \approx 2.4\,$K was observed in magnetization and specific heat measurements. The upper critical fields for two different orientations were determined as $H^{\parallel}_{\mathrm{c2}}(0)\approx 6.3\,$kOe for in-plane and $H^{\perp}_{\mathrm{c2}}(0)\approx 4.7\,$kOe for out-of-plane magnetic fields. Robust superconductivity was also found in resistance and point contact measurements, where the latter showed a slight enhancement of the critical temperature up to $T_\mathrm{c} \sim 3\,$K. Finally, ARPES measurements corroborate the centrosymmetric structure of our samples, showing a single surface termination and the absence of Fermi arcs. △ Less

Submitted 25 August, 2026; originally announced August 2026.

Comments: 9 pages, 7 figures

Chiral Phonons and Giant Anisotropic Photoresponse in Quasi-1D van der Waals Semiconductor ZrSnS3

Authors: Zahir Muhammad, Shashi B. Mishra, Gayatri, Grzegorz Krasucki, Wajid Ali, Katarzyna Olkowska-Pucko, Obaid Iqbal, Zia Ur Rehman, Aziz Ur Rahman, Maciej R. Molas, Lin Xiaoyang, Weisheng Zhao

Abstract: Low-dimensional van der Waals semiconductors with reduced symmetry provide a unique platform for exploring anisotropic physical properties. The quasi-one-dimensional family MXQ$_3$ (M = Hf, Zr; X = Sn; Q = S, Se) exhibits notable structural anisotropy, where zigzag atomic chains influence optical phenomena such as birefringence. This study investigates anisotropic lattice dynamics in ZrSnS$_3$ usi… ▽ More Low-dimensional van der Waals semiconductors with reduced symmetry provide a unique platform for exploring anisotropic physical properties. The quasi-one-dimensional family MXQ$_3$ (M = Hf, Zr; X = Sn; Q = S, Se) exhibits notable structural anisotropy, where zigzag atomic chains influence optical phenomena such as birefringence. This study investigates anisotropic lattice dynamics in ZrSnS$_3$ using angle- and polarization-dependent Raman spectroscopy. Temperature-dependent measurements reveal anharmonic phonon behavior, indicating strong phonon-phonon coupling. Density functional theory calculations show good agreement with the experimentally observed Raman spectra, validating the microscopic description of the lattice dynamics. We also observe a helicity-dependent intensity and a reversal in phonon intensity between lower- and higher-frequency modes under circularly polarized light, which is characteristic of chiral phonons governed by the polarization of the Zr/Sn chains. Our first-principles analysis further shows that angular-momentum-like phonon textures can emerge away from the $Γ$-point near mode-hybridization and avoided-crossing regions, providing microscopic insight into the observed helicity-dependent Raman signatures. Furthermore, we fabricate an optoelectronic device from a thin ZrSnS$_3$ nanowire, demonstrating a photoresponsivity of 50~mA/W under 520~nm laser excitation (1~mW/cm$^2$). The device exhibits a pronounced, power-scalable anisotropic photoresponse with a clear preferred polarization direction. These results highlight the coupling mechanisms between polarization, lattice vibrations, and charge carriers in ZrSnS$_3$, establishing it as a promising material for polarization-sensitive optoelectronics and directional quantum transport. △ Less

Submitted 23 August, 2026; originally announced August 2026.

Comments: 15 pages, 6 figures, and 7 supplemental figures

Robust Discovery of Coarse-Grained Continuum Equations from Microscopic Dynamics

Authors: Partha Sarathi Mondal, Manav Kumar Jalan, Anish Kumar, Shradha Mishra

Abstract: The discovery of governing partial differential equations (PDEs) directly from spatiotemporal data has emerged as a powerful tool for understanding the dynamics of complex systems. In this work, we apply PDE-SINDy to well-known phase-separating systems and examine how its performance depends on the amount of available data, the size of the function library, and the presence of noise. Our results s… ▽ More The discovery of governing partial differential equations (PDEs) directly from spatiotemporal data has emerged as a powerful tool for understanding the dynamics of complex systems. In this work, we apply PDE-SINDy to well-known phase-separating systems and examine how its performance depends on the amount of available data, the size of the function library, and the presence of noise. Our results show that the accuracy of equation discovery depends strongly on the amount of available data. Although the correct equation can be identified with limited data, several spurious terms also acquire finite selection probabilities. As the amount of data increases, these spurious terms are progressively suppressed, leading to a more robust identification of the governing equation. In contrast, increasing the size of the function library adversely affects the efficiency of equation discovery. Further, for the Glauber spin-flip Ising model, we show that the selection probabilities reveal a hierarchy of equations with varying levels of complexity. A sufficiently stringent selection threshold recovers a Model-A-like dynamical equation that accurately reproduces the dynamical and statistical features of phase separation and domain growth. △ Less

Submitted 4 August, 2026; originally announced August 2026.

Comments: 14 pages, 12 figures

Anharmonicity and Nonadiabaticity in Hydride Superconductors

Authors: Shashi B. Mishra, Francesco Belli, Eva Zurek, Elena R. Margine

Abstract: We study superconductivity in representative hydrides using anharmonic phonons, electron-phonon vertex corrections, and full-bandwidth Eliashberg theory. The high-pressure binary hydrides H3S, YH6, and YH9 must be treated with both anharmonic and nonadiabatic corrections, whereas the ambient-pressure PdH/PdD/PdT series is strongly anharmonic but remains adiabatic, reproducing the inverse isotope e… ▽ More We study superconductivity in representative hydrides using anharmonic phonons, electron-phonon vertex corrections, and full-bandwidth Eliashberg theory. The high-pressure binary hydrides H3S, YH6, and YH9 must be treated with both anharmonic and nonadiabatic corrections, whereas the ambient-pressure PdH/PdD/PdT series is strongly anharmonic but remains adiabatic, reproducing the inverse isotope effect without sizable vertex contributions. LaBeH8 exhibits weak anharmonicity, while vertex corrections reduce the critical temperature (Tc) by approximately 4 K, leaving the predicted Tc above experiment. To identify when treatments beyond harmonic, adiabatic Migdal-Eliashberg theory are required, we introduce the anharmonic renormalization $A_λ$ and the vertex ratio $R_{V}$ as material-specific diagnostics. △ Less

Submitted 14 August, 2026; originally announced August 2026.

Comments: 21 pages, 15 figures

Evolution of the Irradiation Induced Defect Landscape through Dislocation Vacancy Loop Interactions in Tungsten

Authors: Soumya Mishra, Suchandrima Das

Abstract: Structural materials for fusion reactors undergo neutron irradiation, generating defect populations that govern their mechanical response through irradiation hardening. Physically based mesoscale constitutive models require accurate descriptions of dislocation defect interactions and, critically, how both defect morphology and obstacle strength evolve during plastic deformation as the irradiation-… ▽ More Structural materials for fusion reactors undergo neutron irradiation, generating defect populations that govern their mechanical response through irradiation hardening. Physically based mesoscale constitutive models require accurate descriptions of dislocation defect interactions and, critically, how both defect morphology and obstacle strength evolve during plastic deformation as the irradiation-induced defect landscape changes. Vacancy loops provide an ideal prototype for addressing this problem because they are among the most prevalent irradiation-induced defects in tungsten, yet their interaction mechanisms with dislocations and subsequent evolution remain poorly understood. Molecular dynamics simulations are used to systematically investigate interactions between edge dislocations and vacancy loops in tungsten by varying loop size, crystallographic orientation, and dislocation loop intersection geometry. Parallel loops exhibit strong geometry dependent behaviour, undergoing complete annihilation, transformation into weaker remnant defects, or defect transport depending on the interaction geometry. In contrast, inclined loops interact through Burgers vector reactions that form sessile <100> dislocation segments, producing substantially higher pinning strengths with little sensitivity to the intersection position. Finally, a framework is demonstrated for translating atomistically determined obstacle strengths into constitutive parameters, such as irradiation hardening, for mesoscale models. The mechanistic understanding developed here provides the physical basis for future mesoscale constitutive laws that explicitly account for the evolution of irradiation-induced defect populations and the resulting changes in dislocation-defect interaction mechanisms and obstacle strength, thereby improving predictive capability beyond calibrated conditions. △ Less

Submitted 29 July, 2026; originally announced July 2026.

Property-Guided Diffusion for Inverse Design of Crystalline Materials

Authors: Sourav Mal, Subhankar Mishra, Prasenjit Sen

Abstract: Diffusion-based generative models with property guidance have emerged as a promising paradigm for inverse materials design by enabling the generation of crystalline materials with user-specified target properties. However, despite recent advances, the effectiveness of property guidance, its influence on crystallographic symmetry, and the physical viability of generated materials remain poorly unde… ▽ More Diffusion-based generative models with property guidance have emerged as a promising paradigm for inverse materials design by enabling the generation of crystalline materials with user-specified target properties. However, despite recent advances, the effectiveness of property guidance, its influence on crystallographic symmetry, and the physical viability of generated materials remain poorly understood. To address these questions, we develop a property-guided framework based on the lightweight diffusion model DiffCrysGen using parameter-efficient adapter fine-tuning and classifier-free guidance (CFG). The resulting framework enables efficient multi-property crystal generation while preserving the knowledge learned during unconditional pre-training. Using formation energy together with saturation magnetization and Vickers hardness as representative inverse-design tasks, we systematically investigate the influence of CFG across a broad range of guidance strengths. Increasing the guidance scale progressively steers the generated property distributions toward the prescribed targets while reducing the fraction of lowest-symmetry ($P1$) structures and increasing the proportion of higher-symmetry structures. To evaluate physical viability, generated structures are geometrically prescreened and subsequently validated using a machine-learning interatomic potential (MLIP)-based workflow comprising structural relaxation and thermodynamic, dynamical, and property-specific analyses. The framework identifies thermodynamically and dynamically stable magnetic and mechanically hard materials with overall success rates of 12.3\% and 3.9\%, respectively. These results establish property-guided DiffCrysGen as an efficient framework for inverse materials design while providing new insights into the role of classifier-free guidance in crystal generation. △ Less

Submitted 23 July, 2026; originally announced July 2026.

Comments: 15 pages, 12 figures

Colored $Δ_T$ noise probes the topological character of edge modes

Authors: Sachiraj Mishra, Colin Benjamin

Abstract: We investigate colored $Δ_T$ noise, i.e., finite-frequency $Δ_T$ noise, as a probe of edge-mode (EM) transport in quantum Hall and quantum spin Hall systems. Colored $Δ_T$ noise probes finite-frequency nonequilibrium current fluctuations and dynamical transport properties that are often obscured in DC measurements of conductance and noise. Since $Δ_T$ noise is driven solely by a temperature and vo… ▽ More We investigate colored $Δ_T$ noise, i.e., finite-frequency $Δ_T$ noise, as a probe of edge-mode (EM) transport in quantum Hall and quantum spin Hall systems. Colored $Δ_T$ noise probes finite-frequency nonequilibrium current fluctuations and dynamical transport properties that are often obscured in DC measurements of conductance and noise. Since $Δ_T$ noise is driven solely by a temperature and voltage bias under zero average charge current conditions, it eliminates current-induced Joule heating and directly probes intrinsic thermal fluctuations. We show that chiral, spin-conserving helical, and spin-flip helical (trivial) EMs exhibit distinct colored $Δ_T$-noise signatures under appropriate bias protocols. Incorporating energy-dependent scattering through a quantum point contact, we demonstrate that electron-hole asymmetry significantly modifies the finite-frequency spectrum while preserving these distinguishing features. Notably, colored $Δ_T$ noise exhibits a frequency-dependent sign reversal absent in the corresponding white ($ω=0$) $Δ_T$ noise. We further investigate zero-temperature colored quantum shot noise and find that it vanishes identically for chiral EMs, whereas the spin-conserving helical response changes sign with frequency. By contrast, spin-flip helical (trivial) EMs exhibit a positive colored shot-noise spectrum. However, the corresponding colored $Δ_T$ noise retains its characteristic sign reversal, providing a robust distinction between spin-conserving helical and spin-flip helical (trivial) EM transport. These results establish colored $Δ_T$ noise as a robust, experimentally accessible, complementary probe for identifying chiral, spin-conserving helical, and spin-flip helical (trivial) EM transport in mesoscopic topological systems. △ Less

Submitted 10 August, 2026; v1 submitted 19 July, 2026; originally announced July 2026.

Comments: 7 pages, 2 figures, 2 tables, accepted for publication in Applied Physics Letters (2026)

Journal ref: Applied Physics Letters (2026)

Density-Induced Reentrant Coarsening in a Two-Temperature System

Authors: Partha Sarathi Mondal, Anish Kumar, Nayana Venkatareddy, Prabal K. Maiti, Shradha Mishra

Abstract: Understanding how nonequilibrium driving modifies phase-separation kinetics remains a fundamental challenge. Here we show that phase separation in a two-temperature system exhibits a striking density-induced reentrant coarsening behavior. Using Brownian dynamics simulations and a coarse-grained field-theoretic model, we find that the characteristic domain size grows as $L(t)\sim t^{1/z}$, displayi… ▽ More Understanding how nonequilibrium driving modifies phase-separation kinetics remains a fundamental challenge. Here we show that phase separation in a two-temperature system exhibits a striking density-induced reentrant coarsening behavior. Using Brownian dynamics simulations and a coarse-grained field-theoretic model, we find that the characteristic domain size grows as $L(t)\sim t^{1/z}$, displaying a reentrant sequence $(t^{1/3} \rightarrow t^{1/4}\rightarrow t^{1/3})$ with increasing density. While the low- and high-density regimes are governed by classical curvature-driven bulk diffusion, the intermediate-density regime exhibits anomalously slow growth. We show that this slowdown originates from a transport bottleneck arising from the interplay of particle diffusivity, particle availability, and attachment kinetics, which suppresses the effective mass flux between domains. Unlike equilibrium phase separation, where density primarily affects morphology and crossover scales, the two-temperature drive renders density a key control parameter for coarsening pathways. Our results uncover a nonequilibrium mechanism for anomalous domain growth in two-temperature systems. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Comments: 5 Pages, 5 Figures

Size focusing in core-shell precipitates: A phase-field study

Authors: Soumya Mishra, T. A. Abinandanan

Abstract: Due to their enhanced resistance to coarsening and/or creep, aluminium alloys with precipitates of two distinct phases in a core-shell morphology are of great contemporary interest. In this paper, we focus on the curious observation in two recent studies on Al-Sc-Li and Al-Yb-Li alloys that growth of the shell phase leads to a narrowing of the size distribution. We have studied this phenomenon, kn… ▽ More Due to their enhanced resistance to coarsening and/or creep, aluminium alloys with precipitates of two distinct phases in a core-shell morphology are of great contemporary interest. In this paper, we focus on the curious observation in two recent studies on Al-Sc-Li and Al-Yb-Li alloys that growth of the shell phase leads to a narrowing of the size distribution. We have studied this phenomenon, known as size focusing, using a theoretical framework (which extends Zener's theory of diffusional growth to a core-shell precipitate) and multi-precipitate simulations based on a phase field model. Our results yield key theoretical insights as well as conclusions with practical significance. (a) On the theoretical front, we show clearly that size focusing is a growth phenomenon: it ends when shell growth ends, and coarsening begins. (b) On the practical front, our results offer guidelines for designing alloys with narrower size distributions: size focusing is promoted in alloys with greater shell volume fractions and greater inter-precipitate spacing. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Coexisting Charge Density Wave and Superconducting Order in Quantizing Magnetic Fields

Authors: Ron Q. Nguyen, Peiyu Qin, Hai-Tian Wu, Sparsh Mishra, Tobias Wolf, Joseph Roll, Erin Morissette, Naiyuan J. Zhang, Sarah Alkidim, Kenji Watanabe, Takashi Taniguchi, Aaron W. Hui, Dima E. Feldman, Allan MacDonald, J. I. A. Li

Abstract: Charge density wave (CDW) and superconductivity are both common in strongly interacting electron systems. While CDW order is ubiquitous in both quantum Hall systems and unconventional superconductors, superconductivity is generally suppressed by the strong magnetic fields required for Landau quantization. Here we investigate the intertwined CDW and superconducting phases of rhombohedral hexalayer… ▽ More Charge density wave (CDW) and superconductivity are both common in strongly interacting electron systems. While CDW order is ubiquitous in both quantum Hall systems and unconventional superconductors, superconductivity is generally suppressed by the strong magnetic fields required for Landau quantization. Here we investigate the intertwined CDW and superconducting phases of rhombohedral hexalayer graphene (R6G) in a large displacement field, which generates tunable flat band edges, and a strong magnetic field, which generates a manifold of nearly degenerate Landau levels. We find a series of integer quantum Hall effects with Hall conductance quantum numbers that deviate from nearby integer filling factors, an observation that can be explained only by CDW order that mixes many Landau levels. We also find a nearby superconducting phase stabilized by perpendicular magnetic fields and persists deep within the quantum Hall regime. This intertwinement provides new insight into superconductivity in R6G at zero magnetic field. △ Less

Submitted 13 August, 2026; v1 submitted 6 July, 2026; originally announced July 2026.

Comments: 11 pages for main text, 4 main figures, total of 31 pages, total of 31 figures

One-dimensional carbon nanostructures with periodic graphitic nitrogen substitution

Authors: Nicolò Bassi, Shantanu Mishra, Zheng Zhang, Xiao-Ye Wang, Feifei Xiang, Nils Krane, Carlo A. Pignedoli, Klaus Müllen, Pascal Ruffieux, Akimitsu Narita, Roman Fasel

Abstract: Heteroatom substitution is a powerful route to tune the chemical and electronic properties of carbon nanomaterials. In particular, replacement of an sp2 hybridized carbon atom in the graphene lattice with a nitrogen atom (denoted as graphitic nitrogen) induces substantial changes in the electronic properties. These include changes in the band structure that can influence electronic transport, and… ▽ More Heteroatom substitution is a powerful route to tune the chemical and electronic properties of carbon nanomaterials. In particular, replacement of an sp2 hybridized carbon atom in the graphene lattice with a nitrogen atom (denoted as graphitic nitrogen) induces substantial changes in the electronic properties. These include changes in the band structure that can influence electronic transport, and magnetism. A key requirement for applications is both the periodic and precise incorporation of the heteroatoms in extended carbon lattices. Here, we report the on-surface synthesis and characterization of two one dimensional carbon nanostructures, a polymer and a graphene nanoribbon, consisting of periodically incorporated graphitic nitrogen atoms. The on-surface reactions toward formation of the nanostructures were monitored by scanning tunneling microscopy. The bond-resolved chemical structures of the reaction intermediates and products were investigated by atomic force microscopy, which enabled atomic-scale visualization of the graphitic nitrogen sites. The electronic properties of the nanostructures were studied by scanning tunneling spectroscopy and density functional theory calculations. Our analyses revealed the presence of localized nitrogen-centered electronic states. In the gas phase where the nanostructures are in a neutral charge state, these states undergo spin polarization leading to an open-shell ground state. Upon adsorption on Au(111), the nanostructures exhibit electron transfer to the surface, which resulted in a closed-shell ground state. Our results demonstrate a straightforward and generally applicable route to synthesize graphitic nitrogen-substituted carbon nanomaterials with potential applications in spintronics, catalysis and energy storage. △ Less

Submitted 3 July, 2026; originally announced July 2026.

Comments: Manuscript: 24 pages and 4 figures; Supporting Information: 19 pages and 18 figures

Selectivity in tip-induced skeletal editing via heteroatom substitution

Authors: Shantanu Mishra, Rasmus Svensson, Valentina Malave, Florian Albrecht, Manuel Vilas-Varela, Henrik Grönbeck, Leo Gross, Diego Peña

Abstract: Skeletal editing enables precise structural modifications of molecules at late stages of a synthetic sequence, with applications in drug discovery and materials science. We recently demonstrated skeletal editing on the single-molecule scale. Voltage pulses applied by the tip of a scanning probe microscope to an oxygen-containing seven-membered heterocycle led to both oxygen deletion and ring-contr… ▽ More Skeletal editing enables precise structural modifications of molecules at late stages of a synthetic sequence, with applications in drug discovery and materials science. We recently demonstrated skeletal editing on the single-molecule scale. Voltage pulses applied by the tip of a scanning probe microscope to an oxygen-containing seven-membered heterocycle led to both oxygen deletion and ring-contraction rearrangement reactions. An open question is whether selective skeletal editing of a heterocyclic core can be achieved by an appropriate choice of the heteroatom. Here, we show that tip-induced reactions of an analogous sulfur-containing seven-membered ring results in sulfur deletion in virtually all cases. Our results demonstrate that the combination of tip-induced chemistry and heteroatom selection in the molecular design is a powerful strategy for single-molecule skeletal editing, with the potential to enable diverse structural transformations of heterocyclic frameworks. △ Less

Submitted 21 June, 2026; originally announced June 2026.

Comments: Manuscript: 8 pages and 4 figures; Supporting Information: 10 pages and 11 figures

Effective masses, Burstein-Moss shift, and bandgap renormalization in degenerate Al-doped ZnO from broadband ellipsometry and Hall measurements

Authors: S. Mishra, L. A. Enrique, D. Cespedes, E. Perez, E. Serquen, F. Bravo, P. Llontop, F. Ruske, L. Korte, J. A. Guerra

Abstract: A comprehensive methodology is developed to extract electron and hole effective masses in degenerate semiconductors through a simultaneous global fit of carrier concentration dependence of bandgap and plasma energy, explicitly incorporating band nonparabolicity. Broadband spectroscopic ellipsometry combined with Hall effect analyses enables accurate determination of the bandgap, plasma energy and… ▽ More A comprehensive methodology is developed to extract electron and hole effective masses in degenerate semiconductors through a simultaneous global fit of carrier concentration dependence of bandgap and plasma energy, explicitly incorporating band nonparabolicity. Broadband spectroscopic ellipsometry combined with Hall effect analyses enables accurate determination of the bandgap, plasma energy and carrier concentrations. The dielectric function of sputtered Al-doped ZnO thin films are modeled in the fundamental absorption region using an Elliott based model with overlapping excitonic transitions and Urbach tails, while free carrier absorption is described by a modified sernelius formula. Wide carrier concentrations are achieved via controlled deposition and post-annealing, revealing changes in electron effective masses and deviations from parabolic dispersion. Two nonparabolic models are compared, Pisarkiewicz, assuming spherically symmetric band with a step-function approximation of the Fermi-Dirac distribution and Nilsson, incorporating thermal and impurity effects. The latter is shown to capture accurately band nonparabolicity, yielding effective masses and nonparabolicity parameter consistent with bandgap evolution. This approach quantitatively separates Burstein-Moss shift and bandgap renormalization, reproducing carrier dependent bandgap shifts across a wide concentration range. Neglecting valence band contributions introduces systematic bias. Bandgap renormalization is further evaluated using plasmon pole and random phase approximations, underscoring the importance of many-body screening. This framework also enables determination of the Mott critical concentration and the fundamental absorption edge onset. Collectively, these results establish a reliable methodology for extracting band-structure parameters and bandgap shifts, extendable to other transparent conducting oxides. △ Less

Submitted 18 June, 2026; originally announced June 2026.

Comments: Supplementary material supporting this manuscript will be available upon reasonable request from contact authors

Probing chaos and thermalization through out-of-time-ordered correlators in random field spin chains

Authors: C Jisha, Shivam Mishra, Ravi Prakash

Abstract: Out-of-time-ordered correlators (OTOCs) have emerged as a diagnostic of information scrambling and quantum chaos in many-body systems. We investigate the imprints of chaos in the dynamics of OTOCs in the Heisenberg spin-$1/2$ chain with random fields. The system is parameterized to exhibit a crossover from integrable to chaotic dynamics. We demonstrate numerically that the approach to saturation o… ▽ More Out-of-time-ordered correlators (OTOCs) have emerged as a diagnostic of information scrambling and quantum chaos in many-body systems. We investigate the imprints of chaos in the dynamics of OTOCs in the Heisenberg spin-$1/2$ chain with random fields. The system is parameterized to exhibit a crossover from integrable to chaotic dynamics. We demonstrate numerically that the approach to saturation of the OTOC can distinguish between integrable and chaotic regimes, with a power-law $(1/t)$ relaxation for integrable systems and a higher-degree power-law decay $(1/t^α; α\ge 1)$ followed by an exponential relaxation for the chaotic regime. We further show that long-range spectral statistics, such as the number variance, are more effective in characterizing quantum chaos in the regime near saturation of OTOC. We also demonstrate that the relaxation and initial scrambling regimes exhibit distinct and universal features, with the former being sensitive and the latter being robust against different realizations of random-fields. The long-time saturation of OTOC also fluctuates with different realizations, and its exact expression is derived through the Eigenstate Thermalization Hypothesis. △ Less

Submitted 17 June, 2026; originally announced June 2026.

Comments: 11 pages, 14 figures

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

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

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

Submitted 15 June, 2026; originally announced June 2026.

Comments: 28 pages, 20 figures

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

Finite-Time Orientational Relaxation Restructures Collective Motion in Polar Active Matter

Authors: Rajneesh Kumar, Subhransu Sekhar Mishra, Debasish Chaudhuri

Abstract: We introduce a Langevin formulation of Vicsek-like active particles in which orientations evolve through finite-rate relaxation toward the local mean direction, with alignment strength $J$ and rotational diffusivity $D_r$, thereby combining Vicsek-type local consensus with XY-like orientational dynamics. Using large-scale numerical simulations, we determine the nonequilibrium phase diagram as a fu… ▽ More We introduce a Langevin formulation of Vicsek-like active particles in which orientations evolve through finite-rate relaxation toward the local mean direction, with alignment strength $J$ and rotational diffusivity $D_r$, thereby combining Vicsek-type local consensus with XY-like orientational dynamics. Using large-scale numerical simulations, we determine the nonequilibrium phase diagram as a function of activity and alignment rate. Increasing the alignment rate drives a sequence of transitions from a homogeneous isotropic state to polar bands, a cross-sea phase of intersecting bands, a homogeneous polar state, and ultimately a micro-clustered regime. The isotropic-to-polar transition is strongly first order, as evidenced by Binder cumulants and bimodal distributions of local polarization and density, indicating coexistence of gas-like and liquid-like regions. Near the onset of collective motion, band size increases with activity but depends non-monotonically on alignment rate. Further increasing the alignment rate drives the system through the cross-sea and homogeneous polar phases before enhanced density fluctuations lead to micro-clustering. Our results demonstrate that finite-time orientational relaxation acts as a control parameter that qualitatively restructures collective behavior in polar active matter. △ Less

Submitted 9 June, 2026; originally announced June 2026.

Comments: 12 pages, 10 figures

Hidden periodicities allow the prediction of locked particle motions on quasicrystalline surfaces

Authors: Seemant Mishra, Artem Ryabov, Philipp Maass

Abstract: Motion of particles across quasicrystalline surfaces exhibits peculiar features due to the presence of long-range order without translational periodicity. Under time-periodic forcing, this motion can become locked in directions thatn deviate strongly from the mean driving direction. We show that for surface potentials with a quasicrystalline pattern of minima generated by a superposition of plane… ▽ More Motion of particles across quasicrystalline surfaces exhibits peculiar features due to the presence of long-range order without translational periodicity. Under time-periodic forcing, this motion can become locked in directions thatn deviate strongly from the mean driving direction. We show that for surface potentials with a quasicrystalline pattern of minima generated by a superposition of plane waves, particle trajectories are nonperiodic, yet their mean direction and speed are determined by hidden periodic potentials. The lattice vectors of these underlying potentials define characteristic velocities that dictate both directional and speed locking. The particle motion does not synchronize with the driving, and it is possible for the mean speed to remain nonlocked even in directionally locked states. These findings are demonstrated using a model directly amenable to experimental realization. △ Less

Submitted 4 June, 2026; originally announced June 2026.

Comments: 6 pages, 4 figures plus 3 pages, 3 figures in supplemental material (included)

Active Control of Topological Exceptional Points in Non-Hermitian Metasurfaces

Authors: Parul Sharma, Sobhan Subhra Mishra, Yash Gupta, Brijesh Kumar, Ranjan Singh, Abhishek Kumar, Anshuman Kumar

Abstract: Active control and ultrafast switching of non-Hermitian photonic systems are essential for next-generation reconfigurable optical technologies. Here, we demonstrate dynamic temporal manipulation of EPs in the terahertz (THz) regime using optically excited germanium (Ge) as an active medium. By exploiting pump-probe delay as a continuous tuning parameter, we achieve sub-picosecond eigenmode switchi… ▽ More Active control and ultrafast switching of non-Hermitian photonic systems are essential for next-generation reconfigurable optical technologies. Here, we demonstrate dynamic temporal manipulation of EPs in the terahertz (THz) regime using optically excited germanium (Ge) as an active medium. By exploiting pump-probe delay as a continuous tuning parameter, we achieve sub-picosecond eigenmode switching (~0.5 ps) and realize a complete time-resolved EP encirclement within ~2 ps, enabling direct observation of topological phase accumulation. At EP, the metasurface exhibits highly asymmetric transmission for circularly polarized light, characteristic of chiral mode response. Furthermore, we observe ultrafast eigenmode switching and topological phase evolution within ~1 ps, achieving >99% cross-polarization modulation depth. The measured results show strong agreement with theoretical modeling, with a high Petermann factor of approximately 10^3, confirming the effectiveness of the design. Our work establishes pump-probe delay time as a dynamical control parameter for EP topology, introducing a new regime of ultrafast non-Hermitian photonics for high-speed switching, enhanced sensitivity, and tunable polarization control in the THz domain. △ Less

Submitted 8 May, 2026; originally announced May 2026.

Phase-Transition Induced Magnetic Domain Evolution and Magnetization Dynamics in FePt/FeRh Bilayers for Advanced Heat-Assisted Magnetic Recording

Authors: Saroj K. Mishra, Y. Sasaki, S. Isogami, I. Suzuki, Keerthana P, J. Mohanty, Y. K. Takahashi

Abstract: Achieving ultrahigh recording densities with low power consumption is a central challenge for next generation heat assisted magnetic recording (HAMR), as conventional L10 FePt media require intense laser heating due to their high coercivity (Hc) and high Curie temperature (700 K). Here, we address this issue using FePt/FeRh bilayers, where the antiferromagnetic to ferromagnetic transition of FeRh… ▽ More Achieving ultrahigh recording densities with low power consumption is a central challenge for next generation heat assisted magnetic recording (HAMR), as conventional L10 FePt media require intense laser heating due to their high coercivity (Hc) and high Curie temperature (700 K). Here, we address this issue using FePt/FeRh bilayers, where the antiferromagnetic to ferromagnetic transition of FeRh near 350 K generates strong interfacial exchange coupling that assists magnetization switching in the FePt layer. Magnetometry measurements reveal a 40% reduction in Hc from 300 K to 400 K in the bilayer, compared to only 8% in single layer FePt. Temperature dependent MFM directly captures phase transition induced domain evolution, showing a 30% reduction in domain size and enhanced phase contrast. TR-MOKE measurements reveal only a minor (0.4 T) modification of the effective anisotropy field during phase transition, confirming that the intrinsic anisotropy of FePt remains largely preserved. These results demonstrate that the reduction in Hc in FePt/FeRh bilayers is primarily governed by phase transition induced domain wall mobility coupled with interfacial magnetic interactions, rather than by intrinsic anisotropy softening. This mechanism provides a pathway toward efficient magnetization switching under reduced thermal load, making FePt/FeRh heterostructures promising candidates for advanced HAMR media. △ Less

Submitted 6 May, 2026; v1 submitted 29 April, 2026; originally announced April 2026.

Comments: 11 pages, 8 figures

Electrically Tunable Terahertz Chirality from Quantum Geometry

Authors: Sobhan Subhra Mishra, Thomas CaiWei Tan, Faxian Xiu, Ranjan Singh

Abstract: Quantum geometry encoded in the momentum space structure of electronic wavefunctions, governs charge dynamics through Berry curvature, enabling unconventional transport and optical responses. In topological semimetals, this geometry is sampled over Fermi pockets, suggesting electrical control by Fermi surface tuning, yet such control has remained largely limited to DC transport. Here we show that… ▽ More Quantum geometry encoded in the momentum space structure of electronic wavefunctions, governs charge dynamics through Berry curvature, enabling unconventional transport and optical responses. In topological semimetals, this geometry is sampled over Fermi pockets, suggesting electrical control by Fermi surface tuning, yet such control has remained largely limited to DC transport. Here we show that electrostatic gating of the 3D Dirac semimetal Cd3As2 reshapes Fermi pockets surrounding photoinduced Floquet Weyl nodes, enabling electrical control of terahertz (THz) emission chirality. Gate tuning selectively modulates the Berry curvature driven linearly polarized THz component by up to 60% and 49% at positive and negative bias, respectively, while the orthogonal linearly polarized photon-drag component remains unchanged. With the two orthogonal fields intrinsically phase-locked at \sfracπ{2} by the excitation geometry, the selective gate-tuned amplitude control enables the polarization tuning across the Poincaré sphere, achieving near-circular polarization (χ\approx-42°) at +10 V. These results establish Fermi surface tuning as a general route to programmable quantum geometric control of chiral terahertz emission. △ Less

Submitted 29 April, 2026; originally announced April 2026.

Non-Equilibrium Orbital Transport in Terahertz Optorbitronics

Authors: Sobhan Subhra Mishra, Ranjan Singh

Abstract: Modern information technologies rely on controlling the flow of electrons through their charge and spin. A rapidly emerging alternative is to use the orbital motion of electrons, the way they circulate around atomic sites as a new carrier of information. This orbital angular momentum (OAM) could enable more energy-efficient devices and reduce reliance on scarce heavy elements, but how orbital curr… ▽ More Modern information technologies rely on controlling the flow of electrons through their charge and spin. A rapidly emerging alternative is to use the orbital motion of electrons, the way they circulate around atomic sites as a new carrier of information. This orbital angular momentum (OAM) could enable more energy-efficient devices and reduce reliance on scarce heavy elements, but how orbital currents are generated and transported, especially on ultrafast timescales, remains largely unknown. In this review, we introduce terahertz optorbitronics, an approach that uses ultrafast femtosecond laser pulses and terahertz radiation to observe orbital transport in real time. On timescales of quadrillionth of a second, this technique allows us to track how orbital currents are launched, propagate, and convert into electrical signals in nanoscale thin-film materials. Surprisingly, recent experiments have revealed conflicting pictures such as orbital currents may travel over tens of nanometres like ballistic waves or instead decay within just a few atomic layers, highlighting a fundamental unresolved question in the field. We explain how these ultrafast measurements can disentangle orbital motion from conventional spin transport, and we highlight new materials from engineered graphene to altermagnets, that could act as tunable sources of orbital currents. We also discuss how light, electrical gating, strain, and interface design can be used to actively control orbital transport and improve its conversion into usable electronic signals. By revealing orbital transport as a dynamic, non-equilibrium process, terahertz optorbitronics opens a new direction for nanoscale science, the one that could lead to faster, more efficient technologies operating beyond the limits of conventional spin-based electronics. △ Less

Submitted 29 April, 2026; originally announced April 2026.

Comments: 27 pages, 5 figures, 1 table

Emergent Rotation of Passive Clusters in a Chiral Active Bath

Authors: Divya Kushwaha, Abhra Puitandy, Shradha Mishra

Abstract: We investigate the dynamics of passive particles immersed in a bath of chiral active particles, focusing on the emergence of collective rotational motion. Using numerical simulations, we show that passive particles aggregate into clusters that can exhibit persistent rotation within a well-defined regime of size ratio and active particle packing fraction. This rotational state is characterized by t… ▽ More We investigate the dynamics of passive particles immersed in a bath of chiral active particles, focusing on the emergence of collective rotational motion. Using numerical simulations, we show that passive particles aggregate into clusters that can exhibit persistent rotation within a well-defined regime of size ratio and active particle packing fraction. This rotational state is characterized by the coexistence of internal structural order, enhanced shape fluctuations, and a coherent net torque generated by the surrounding active bath. Outside this regime, the dynamics remain predominantly diffusive, highlighting that sustained rotation is not ubiquitous but arises from a delicate interplay between geometry, activity, and chirality. Furthermore, we demonstrate that chirality heterogeneity disrupts rotational coherence, while a uniform chiral bath promotes strongly superdiffusive angular dynamics. These results provide new insights into the role of chirality and collective interactions in shaping the emergent behavior of active-passive mixtures. △ Less

Submitted 25 July, 2026; v1 submitted 7 April, 2026; originally announced April 2026.

Temperature-Bias Noise and Quantum Shot Noise as Probes of Pairing Symmetry in Iron Pnictides

Authors: Sachiraj Mishra, A Rajmohan Dora, Colin Benjamin

Abstract: Quantum noise has long served as a powerful probe of quantum transport in mesoscopic junctions. Recently, temperature-driven noise, or $Δ_T$ noise, has attracted growing interest due to its presence even in the absence of average charge current. In this work, we investigate a normal metal-insulator-iron-pnictide junction and demonstrate how zero temperature quantum shot noise, finite temperature q… ▽ More Quantum noise has long served as a powerful probe of quantum transport in mesoscopic junctions. Recently, temperature-driven noise, or $Δ_T$ noise, has attracted growing interest due to its presence even in the absence of average charge current. In this work, we investigate a normal metal-insulator-iron-pnictide junction and demonstrate how zero temperature quantum shot noise, finite temperature quantum noise and $Δ_T$ noise can discriminate between $S_{++}$ and $S_{+-}$ pairing symmetries, which are relevant to iron-based superconductors. We introduce $Δ_T$ noise as a novel probe for distinguishing between the two pairing symmetries. In contrast to conductance, which exhibits a single peak for both $S_{++}$ and $S_{+-}$ states with only a difference in magnitude, the $Δ_T$ noise reveals qualitatively distinct features: a twin-peak structure for the $S_{++}$ pairing symmetry and a single-peak profile for the $S_{+-}$ state. A similar symmetry-dependent contrast is observed in both zero temperature quantum shot noise and finite temperature quantum noise, where the $S_{++}$ state consistently exhibits a twin-peak structure, while the $S_{+-}$ state shows a single-peak response. Our results demonstrate that noise-based measurements form a mutually reinforcing set of probes that enables reliable identification of superconducting gap symmetry in Iron Pnictide superconductors. △ Less

Submitted 23 July, 2026; v1 submitted 20 March, 2026; originally announced March 2026.

Comments: 21 pages, 11 figures, 1 table; accepted for publication in Journal of Applied Physics (2026)

Journal ref: Journal of Applied Physics 140, 063905 (2026)

Charge-ordered states in twisted MoTe$_2$

Authors: Sparsh Mishra, Tobias M. R. Wolf, Allan H. MacDonald

Abstract: We analyze interaction-driven charge-density-wave (CDW) states in the spin-valley polarized first valence miniband of twisted MoTe$_2$ (tMoTe$_2$) using an adiabatic mapping from the continuum model to an effective Landau-level (LL) problem. When projected to the lowest LL, the leading spatial harmonic of the moiré-periodic potential changes sign at a magic twist angle $θ_c$ where the band reaches… ▽ More We analyze interaction-driven charge-density-wave (CDW) states in the spin-valley polarized first valence miniband of twisted MoTe$_2$ (tMoTe$_2$) using an adiabatic mapping from the continuum model to an effective Landau-level (LL) problem. When projected to the lowest LL, the leading spatial harmonic of the moiré-periodic potential changes sign at a magic twist angle $θ_c$ where the band reaches its minimum bandwidth. By solving self-consistent Hartree-Fock equations in a multi-LL Hilbert space, we find that triangular-lattice CDW states with density maxima on MX (or XM) sites or on MM sites are favored on opposite sides of the magic angle at most filling factors and that stripe order appears near $ν_h=1/2$. We show that CDW states at $ν_h >1/2$ can carry a nonzero total Chern number, providing a natural route to reentrant integer quantum Hall effects and discuss the energy competition between fractional Chern insulator and CDW states. △ Less

Submitted 9 March, 2026; v1 submitted 5 March, 2026; originally announced March 2026.

Comments: 6 pages, 3 figures, Supplementary material 9 pages (typos corrected)

Thickness-Driven Control of Room Temperature Ferrimagnetic Skyrmions and their Topological Hall signature in GdFe Single Layers

Authors: Saroj Kumar Mishra, Y. K. Takahashi, C. Malavika, Karthik V. Raman, Jyoti Ranjan Mohanty

Abstract: Magnetic skyrmions are nanoscale, topologically protected spin textures with exceptional potential for high density data storage and energy efficient computing. Among various skyrmion hosting systems, rare earth transition metal ferrimagnets offer a promising platform due to their tunable magnetic properties and intrinsically low net magnetization. Despite this, the fundamental control of ferrimag… ▽ More Magnetic skyrmions are nanoscale, topologically protected spin textures with exceptional potential for high density data storage and energy efficient computing. Among various skyrmion hosting systems, rare earth transition metal ferrimagnets offer a promising platform due to their tunable magnetic properties and intrinsically low net magnetization. Despite this, the fundamental control of ferrimagnetic skyrmions in single layer films remains unexplored. Here, we demonstrate a viable route for engineering room temperature skyrmions in GdFe single layers through precise control of film thickness (60 to 80 nm). Thickness variation enables the systematic tuning of key magnetic parameters, including perpendicular magnetic anisotropy and saturation magnetization, thereby allowing precise control over skyrmion size and density. Magnetic force microscopy (MFM) reveals a clear thickness dependent evolution of isolated skyrmion characteristics, where skyrmion size decreases while skyrmion density increases with increasing GdFe film thickness, in agreement with micromagnetic simulations. At the same time, magnetotransport measurements show a systematic enhancement in the topological Hall resistivity with thickness, further corroborating the increased skyrmion density observed in MFM. Scanning transmission electron microscopy reveals a compositional gradient across the film thickness, indicative of structural asymmetry and potential inversion symmetry breaking, contributing to the emergence of a bulk Dzyaloshinskii Moriya interaction. Notably, sub 60nm skyrmions with high areal density are stabilized at room temperature. This work provides a viable route to tailor the properties of ferrimagnetic skyrmions in single-layer GdFe films, paving the way for the development of high-density ferrimagnetic skyrmionic devices. △ Less

Submitted 25 February, 2026; originally announced February 2026.

Comments: 20pages, 7 figures

High-Tc Superconductivity in Functionalized Out-of-Plane Ordered Double Transition Metal MXenes

Authors: Mohammad Keivanloo, Fateme Dinmohammad, Shashi B. Mishra, Mohammad Sandoghchi, Mohammad Javad Arshia, Mitsuaki Kawamura, Elena R. Margine, Muhammad Haris Mahyuddin, Hannes Raebiger, Reza Pamungkas Putra Sukanli, Kenta Hongo, Ryo Maezono, Mohammad Khazaei

Abstract: Two-dimensional (2D) superconductors attracted growing interest in condensed-matter physics research. In this work, we explore the superconducting properties of surface-functionalized, out-of-plane ordered double transition-metal MXenes (o-MXenes), which exhibit distinctive structural and electronic characteristics. Using first-principles calculations, we investigate the effects of electronic stru… ▽ More Two-dimensional (2D) superconductors attracted growing interest in condensed-matter physics research. In this work, we explore the superconducting properties of surface-functionalized, out-of-plane ordered double transition-metal MXenes (o-MXenes), which exhibit distinctive structural and electronic characteristics. Using first-principles calculations, we investigate the effects of electronic structure, electron-phonon coupling (EPC), anharmonicity, and anisotropy effect in superconductivity properties of o-MXenes. We examine a wide range of o-MXene systems, M$_{2}$M$^\prime$X$_{2}$T$_{2}$ (M = Mo, W; M$^\prime$ = Sc, Ti, V, Mo, Zr, Nb, Ta; X = C, N), functionalized with F, O, Cl, and H groups. Out of 128 candidates, 32 compounds are found to be mechanically, dynamically, and thermodynamically stable, exhibiting superconducting transition temperatures (T$_{c}$) from 0.1 K to 52 K. Notably, the Mo$_{2}$ScN$_{2}$O$_{2}$ compound achieves the highest T$_{c}$ of 52 K, with a superconducting gap of $\sim$10 meV. Solving the anisotropic Eliashberg equation reveals that Mo$_{2}$ScN$_{2}$O$_{2}$ is an anisotropic two-gap superconductor, and incorporating anharmonic effects decreases its T$_{c}$ slightly. We further analyze flat-band-induced EPC enhancement and present EPC matrix elements as functions of phonon wavevector q for distinct vibrational modes that show anharmonic behavior of these materials. △ Less

Submitted 13 February, 2026; originally announced February 2026.

Atomically-sharp magnetic soliton in the square-net lattice EuRhAl$_{4}$Si$_{2}$

Authors: Kevin Allen, Juba Bouaziz, Yichen Zhang, Kai Du, Sanu Mishra, Gustav Bihlmayer, Yiqing Hao, Victor Ukleev, Chen Luo, Florin Radu, Yuxiang Gao, Marta Zonno, Sergey Gorovikov, Christopher Lane, Jian-Xin Zhu, Huibo Cao, Sang-Wook Cheong, Ming Yi, Stefan Blügel, Emilia Morosan

Abstract: Topological spin textures are hallmark manifestations of competing interactions in magnetic matter. Their effective description by nonlinear field theories reflects an energetic frustration that destabilizes uniform order while selecting finite-size, topologically nontrivial configurations as stationary states. Among the most extreme realizations are atomically-sharp domain wall excitations, namel… ▽ More Topological spin textures are hallmark manifestations of competing interactions in magnetic matter. Their effective description by nonlinear field theories reflects an energetic frustration that destabilizes uniform order while selecting finite-size, topologically nontrivial configurations as stationary states. Among the most extreme realizations are atomically-sharp domain wall excitations, namely one-dimensional (1D) magnetic solitons, which represent the ultimate scaling limit of magnetic textures. Such solitons may emerge in magnetic systems where effective exchange interactions compete directly with uniaxial magnetic anisotropy. Here we show that the square-net rare earth compound EuRhAl$_{4}$Si$_{2}$ realizes a very susceptible regime where the magnetic anisotropy competes with highly frustrated exchange interactions stabilizing a rare ferrimagnetic $\uparrow\uparrow\downarrow$ state that, under applied magnetic field, supports the formation of atomically-sharp soliton defects. We confirm the bulk response of the 1D magnetic solitons via magnetization and electrical transport measurements. We establish both the zero- and in-field $\uparrow\uparrow\downarrow$ order via neutron diffraction, while magnetic force microscopy visualizes its real-space evolution into a stripe-like array. To elucidate the microscopic origin of the soliton, we relate the Ruderman-Kittel-Kasuya-Yosida (RKKY)-driven exchange interactions and the magnetic anisotropy through density functional theory, and we construct an effective 1D $J_{1}$-$J_{2}$-$K$ model whose atomistic spin dynamics simulations reproduce the observed soliton states as a function of external field. Our results demonstrate that EuRhAl$_{4}$Si$_{2}$ hosts atomically-sharp, field-driven 1D magnetic solitons, providing a new platform for studying 1D topological excitations at the atomic length scale. △ Less

Submitted 10 February, 2026; originally announced February 2026.

Homing through Reinforcement Learning

Authors: Riya Singh, Pratikshya Jena, Anish Kumar, Shradha Mishra

Abstract: Homing and navigation are fundamental behaviors in biological systems that enable agents to reliably reach a target under uncertainty. We present a Reinforcement Learning (RL) framework to model adaptive homing in continuous two-dimensional domain. In this framework, the agent's state is given by its angular deviation from home, actions correspond to alignment or stochastic reorientation, and lear… ▽ More Homing and navigation are fundamental behaviors in biological systems that enable agents to reliably reach a target under uncertainty. We present a Reinforcement Learning (RL) framework to model adaptive homing in continuous two-dimensional domain. In this framework, the agent's state is given by its angular deviation from home, actions correspond to alignment or stochastic reorientation, and learning is driven by a radial-distance-based cost that penalizes motion away from the target, where the cost also acts as an effective signal guiding the agent towards the home. For a single self-propelled agent moving with constant speed, we find that the mean homing time $\langle T_{\mathrm{home}} \rangle$ exhibits a non-monotonic dependence on the rotational diffusion strength $D_r$, with an optimal noise level $D_r^\ast$, revealing a subtle interplay between exploration and goal-directed correction. Extending to two agents with soft repulsion, one agent consistently reaches home faster than the other, while in multi-agents system, repulsion ensures separation and the fastest agent becomes progressively faster as group size increases. Finally, we have compared the homing time obtained from the RL agent with that of an Active Brownian Particle (ABP) with resetting and a pure ABP (without resetting) under identical conditions. The RL-based agent consistently achieves shorter homing times with trajectories that are less noisy and more directed than both cases, while the pure ABP typically continues wandering near the target without reliable localization. Our results show that cost-driven learning, stochastic reorientation, and inter-agent interactions enable efficient adaptive navigation, linking individual and collective homing. This RL framework captures key biological features such as feedback-based route learning, randomness to escape unfavorable orientations, and mutual coordination. △ Less

Submitted 30 June, 2026; v1 submitted 9 February, 2026; originally announced February 2026.

Pressure induced electronic band evolution and observation of superconductivity in the Dirac semimetal ZrTe5

Authors: Sanskar Mishra, Nagendra Singh, Vinod K. Gangwar, Rajan Walia, Jianping Sun, Genfu Chen, Dilip Bhoi, Sandip Chatterjee, Yoshiya Uwatoko, Jinguang Cheng, Prashant Shahi

Abstract: We report a comprehensive investigation of the pressure effects on the magnetotransport properties of the topological material ZrTe5 within 1 to 8 GPa pressure range. With increasing pressure, the characteristic peak (Tp) in its electrical resistivity first shifts to higher temperature and then moves quickly towards the lower temperature before disappearing eventually at 6 GPa. Beyond 6 GPa, the s… ▽ More We report a comprehensive investigation of the pressure effects on the magnetotransport properties of the topological material ZrTe5 within 1 to 8 GPa pressure range. With increasing pressure, the characteristic peak (Tp) in its electrical resistivity first shifts to higher temperature and then moves quickly towards the lower temperature before disappearing eventually at 6 GPa. Beyond 6 GPa, the system exhibits metallic behavior across the entire temperature range, and superconductivity emerges below Tc = 1.8 K at 8 GPa. Based on the systematic magnetotransport measurement under pressure, we demonstrate that the superconductivity occurs following a significant electronic structure modulation possibly due to pressure induced structural changes near 6 GPa, which coincides with dramatic enhancement of the magnetoresistance (MR) reaching up to 1400 percent. Our experimental results are substantiated by density functional theory calculations as the application of pressure drastically alters the density of states near the Fermi level. Notably, multiple hole pockets emerge at the Fermi level from 4 GPa onward, and their contributions are further enhanced with increasing pressure. The combined experimental and theoretical investigation reveals a comprehensive evolution of electronic structure of Dirac semimetal ZrTe5 under pressure and suggest a possible link between the Fermi surface reconstruction in the pressure range of structural transition and emergence of superconductivity △ Less

Submitted 9 February, 2026; originally announced February 2026.

Comments: 14 Pages, 16 Figures

Report number: 195113

Journal ref: Physical Review B 113, 195113 (2026)

Controlling HER activity and stability of $γ$- and 6,6,12-Graphyne through engineered B-N doping: DFT and Reactive MD simulations

Authors: Juan Gomez Quispe, Matheus Medina, Subhendu Mishra, Douglas S Galvao, Abhishek Singh, Pedro Alves da Silva Autreto

Abstract: Graphynes offer a chemically heterogeneous $sp/sp^{2}$ carbon framework with distinct electronic regimes and site-selective reactivity. Here, Density Functional Theory and Reactive Molecular Dynamics Simulations are combined to evaluate pristine, B-doped, N-doped, and B-N co-doped $γ$-graphyne and 6,6,12-graphyne (meta/ortho/para). $γ$-graphyne is a semiconductor, while 6,6,12-graphyne exhibits an… ▽ More Graphynes offer a chemically heterogeneous $sp/sp^{2}$ carbon framework with distinct electronic regimes and site-selective reactivity. Here, Density Functional Theory and Reactive Molecular Dynamics Simulations are combined to evaluate pristine, B-doped, N-doped, and B-N co-doped $γ$-graphyne and 6,6,12-graphyne (meta/ortho/para). $γ$-graphyne is a semiconductor, while 6,6,12-graphyne exhibits an anisotropic Dirac-like semi-metallic dispersion. B/N substitution reconstructs near-$E_F$ states via dopant $π$ hybridization, and B-N pairing stabilizes defects through donor-acceptor compensation, with the ortho substitutions being the most favorable. Hydrogen adsorption remains weak on pristine lattices but becomes locally optimized upon doping, with near thermo-neutral $ΔG_{\mathrm{ads}}$ 'hot spots' predominantly on $sp$-proximate carbon sites adjacent to the dopants. Reactive MD at 300 K further reveals an activity stability trade-off: B-N ortho in $γ$-graphyne sustains controlled hydrogen uptake without catastrophic bond scission, whereas B-N meta/para degrade, and 6,6,12-graphyne is generally more susceptible to over-hydrogenation. These results identify the B-N geometry as a key design variable for graphyne-based HER catalysts, which require both a favorable $ΔG_{\mathrm{ads}}$ and finite-temperature hydrogenation stability. △ Less

Submitted 21 January, 2026; originally announced January 2026.

Comments: submitted

Eigenstate Thermalization and Spectral Imprints of the Hamiltonian in Local Observables

Authors: Shivam Mishra, C Jisha, Ravi Prakash

Abstract: The Eigenstate Thermalization Hypothesis explains thermalization in isolated quantum systems through the statistical properties of observables in the energy eigenbasis. We investigate the crossover from integrability to chaos in the spin-$1/2$ XXZ chain, establishing a direct correspondence between the spectral correlations of the Hamiltonian and local observables expressed in the energy eigenbasi… ▽ More The Eigenstate Thermalization Hypothesis explains thermalization in isolated quantum systems through the statistical properties of observables in the energy eigenbasis. We investigate the crossover from integrability to chaos in the spin-$1/2$ XXZ chain, establishing a direct correspondence between the spectral correlations of the Hamiltonian and local observables expressed in the energy eigenbasis as a signature of ergodicity breaking. By introducing a local perturbation that drives the system from integrability to chaos, we track the standard ETH indicators and the eigenstate entanglement entropy. We introduce a submatrix-based framework for analyzing local observables in the energy eigenbasis. By extracting real-symmetric blocks along the diagonal of the local observables represented in eigenbasis, we show that these submatrices exhibit both the short-range and long-range spectral features of the Hamiltonian. Remarkably, this correspondence persists even in a partially ergodic regime, indicating that the emergence of chaos is already encoded locally within the observables' matrix structure and that small blocks are sufficient to capture the underlying spectral correlations. △ Less

Submitted 14 January, 2026; originally announced January 2026.

Comments: 14 pages, 13 figures

$Δ_T$ Noise from Electron-Hole Asymmetry in Normal and Superconducting Quantum Point Contacts

Authors: Sachiraj Mishra, Colin Benjamin

Abstract: This work examines $Δ_T$ noise in two-terminal hybrid nanostructures featuring a quantum point contact (QPC), realized either between two normal metals (NQN) or between a normal metal and a superconductor (NQS). The inclusion of a QPC breaks electron-hole (e-h) symmetry, leading to a finite thermovoltage. In contrast, earlier studies on hybrid junctions incorporating insulating barriers, as e-h sy… ▽ More This work examines $Δ_T$ noise in two-terminal hybrid nanostructures featuring a quantum point contact (QPC), realized either between two normal metals (NQN) or between a normal metal and a superconductor (NQS). The inclusion of a QPC breaks electron-hole (e-h) symmetry, leading to a finite thermovoltage. In contrast, earlier studies on hybrid junctions incorporating insulating barriers, as e-h symmetry is preserved, have vanishing thermovoltage, and consequently, $Δ_T$ noise is calculated at zero thermovoltage. In our setup, the broken e-h symmetry allows for a finite thermovoltage, at which we compute the corresponding $Δ_T$ noise. Unlike earlier studies restricted by e-h symmetry and vanishing thermovoltage, our work establishes a self-consistent framework in mesoscopic hybrid junctions, revealing how Andreev reflection fundamentally reshapes $Δ_T$ noise once e-h symmetry is broken. This broad access to charge fluctuation signatures provides a more comprehensive understanding of non-equilibrium transport in linear response. To our knowledge, this work provides the first self-consistent analysis of $Δ_T$ noise in superconducting hybrid junctions where e-h symmetry is broken, explicitly revealing how Andreev reflection modifies $Δ_T$ noise beyond the symmetry-protected zero-thermovoltage regime. △ Less

Submitted 1 January, 2026; originally announced January 2026.

Comments: 15 pages, 9 figures, 1 table

Coexistence of inequivalent time-crystalline orders in a Floquet collective spin system

Authors: Shashank Mishra, Sayan Choudhury

Abstract: We investigate the dynamical phases that emerge in collective spin models subjected to a spatially non-uniform periodic drive. Taking the paradigmatic Lipkin-Meshkov-Glick (LMG) model as a concrete platform, we establish that a rich landscape of dynamical phases emerges when two regions of the system are driven with different field strengths, $h_1$ and $h_2$. Remarkably, despite the `all-to-all' n… ▽ More We investigate the dynamical phases that emerge in collective spin models subjected to a spatially non-uniform periodic drive. Taking the paradigmatic Lipkin-Meshkov-Glick (LMG) model as a concrete platform, we establish that a rich landscape of dynamical phases emerges when two regions of the system are driven with different field strengths, $h_1$ and $h_2$. Remarkably, despite the `all-to-all' nature of the interactions, the system can be driven into dynamical phases characterized by distinct kinds of discrete time crystal (DTC) orders in different parts of the system. Apart from these coexisting DTCs, tuning the driving field leads to the emergence of phases where DTCs coexist with Floquet-synchronized or oscillatory phases; the former has been dubbed a chimera DTC. Finally, we demonstrate that a tunable set of global DTC phases emerges when $h_1$ and $h_2$ are proximate. Crucially, these dynamical regimes can be observed both for experimentally relevant finite-size systems and in the thermodynamic limit. Our results establish spatially structured driving as a powerful route to realize non-equilibrium phase coexistence in collective spin systems. △ Less

Submitted 21 June, 2026; v1 submitted 23 December, 2025; originally announced December 2025.

Comments: 7+6 pages, 3+4 figures

Spatiotemporal Chaos and Defect Proliferation in Polar-Apolar Active Mixture

Authors: Partha Sarathi Mondal, Tamas Vicsek, Shradha Mishra

Abstract: Chaotic transitions in inertial fluids typically proceed through a direct energy cascade from large to small scales. In contrast, active systems, composed of self propelled units, inject energy at microscopic scales and therefore exhibit an inverse cascade, giving rise to distinctly unconventional flow patterns. Here, we investigate an active mixture consisting of both apolar and polar self driven… ▽ More Chaotic transitions in inertial fluids typically proceed through a direct energy cascade from large to small scales. In contrast, active systems, composed of self propelled units, inject energy at microscopic scales and therefore exhibit an inverse cascade, giving rise to distinctly unconventional flow patterns. Here, we investigate an active mixture consisting of both apolar and polar self driven components, a setting expected to display richer behaviours than those found in living liquid crystal (LLC) systems, where the apolar constituent is passive. Using numerical solutions of the corresponding hydrodynamic equations, we uncover a variety of complex dynamical states. Our results reveal a non-monotonic response of the apolar species to changes in the density and activity of the polar component. In an intermediate regime, reminiscent of LLC-induced disorder, the system develops a dynamically disordered phase characterised by high-density, chaotically evolving band-like structures and by the continual creation and annihilation of half integer topological defects. We show that this regime exhibits spatiotemporal chaos, which we quantify through two complementary measures: the spectral properties of density fluctuations and the maximal Lyapunov exponent. Together, these findings broaden the understanding of complex transitions in active matter and suggest potential experimental realisations in bacterial suspensions or synthetic microswimmer assemblies. △ Less

Submitted 13 April, 2026; v1 submitted 23 December, 2025; originally announced December 2025.

Comments: 22 pages, 20 figures (Accepted in New Journal of Physics)

Phase separation kinetics of 2-TIPS at low density: Cluster growth by ballistic agglomeration

Authors: Nayana Venkatareddy, Partha Sarathi Mondal, Shradha Mishra, Prabal K. Maiti

Abstract: We study the kinetics of two-temperature induced phase separation (2-TIPS) in dilute binary mixtures of active ("hot") and passive ("cold") particles using molecular dynamics simulations and a coarse-grained hydrodynamic model. Following a temperature quench, cold particles nucleate into mobile clusters that move ballistically and merge through successive coalescence events. The resulting domain g… ▽ More We study the kinetics of two-temperature induced phase separation (2-TIPS) in dilute binary mixtures of active ("hot") and passive ("cold") particles using molecular dynamics simulations and a coarse-grained hydrodynamic model. Following a temperature quench, cold particles nucleate into mobile clusters that move ballistically and merge through successive coalescence events. The resulting domain growth exhibits dynamic scaling with a growth exponent of approximately 0.7, markedly faster than diffusive coarsening. We identify this regime as ballistic agglomeration of cold clusters, demonstrating a distinct nonequilibrium growth mechanism in low-density scalar active systems. △ Less

Submitted 21 December, 2025; originally announced December 2025.

Comments: 6 pages, 4 figures

Machine Learning-Guided Discovery of Kagome Superconductors YRu3B2 and LuRu3B2

Authors: Rose Albu Mustaf, Sajilesh K. P., Sanu Mishra, Junze Deng, Yi Jiang, Kaja H. Hiorth, Eeli O. Lamponen, Martin Gutierrez-Amigo, Päivi Törmä, Miguel A. L. Marques, B. Andrei Bernevig, Emilia Morosan

Abstract: We report the experimental discovery of bulk superconductivity in two kagome lattice compounds, YRu$_3$B$_2$ and LuRu$_3$B$_2$, which were predicted through machine learning-accelerated high-throughput screening combined with first principles calculations. These materials crystallize in the hexagonal CeCo$_3$B$_2$-type structure with planar kagome networks formed by Ru atoms. We observe supercondu… ▽ More We report the experimental discovery of bulk superconductivity in two kagome lattice compounds, YRu$_3$B$_2$ and LuRu$_3$B$_2$, which were predicted through machine learning-accelerated high-throughput screening combined with first principles calculations. These materials crystallize in the hexagonal CeCo$_3$B$_2$-type structure with planar kagome networks formed by Ru atoms. We observe superconducting critical temperatures of $T_{c} = 0.81$~K for YRu$_3$B$_2$ and $T_{c} = 0.95$~K for LuRu$_3$B$_2$, confirmed through magnetization and specific heat measurements. Both compounds exhibit nearly 100\% superconducting volume fractions, demonstrating bulk superconductivity. Compared with LaRu$_3$Si$_2$, YRu$_3$B$_2$ and LuRu$_3$B$_2$ show a more dispersive Ru local $d_{x^2-y^2}$ quasi-flat band (and thus a reduced DOS at $E_F$) together with an overall hardening of the phonon spectrum, both of which lower the electron-phonon coupling (EPC) constant $λ$. Meanwhile, the dominant real-space EPC between Ru local $d_{x^2-y^2}$ states and the low-frequency Ru in-plane local $x$ branch remains nearly unchanged, indicating that the reduction of $λ$ originates from the $d_{x^2-y^2}$ DOS reduction and the overall phonon hardening. Superfluid weight calculations show that conventional contributions dominate over quantum geometric effects due to the dispersive nature of bands near the Fermi level. This work demonstrates the effectiveness of integrating machine learning screening, first principles theory, and experimental synthesis for accelerating the discovery of new superconducting materials. △ Less

Submitted 4 February, 2026; v1 submitted 16 December, 2025; originally announced December 2025.

Disentangling the unusual magnetic anisotropy of the near-room-temperature ferromagnet Fe$_{4}$GeTe$_{2}$

Authors: Riju Pal, Joyal J. Abraham, Alexander Mistonov, Swarnamayee Mishra, Nina Stilkerich, Suchanda Mondal, Prabhat Mandal, Atindra Nath Pal, Jochen Geck, Bernd Büchner, Vladislav Kataev, Alexey Alfonsov

Abstract: In the quest for two-dimensional conducting materials with high ferromagnetic ordering temperature the new family of the layered Fe$_{n}$GeTe$_{2}$ compounds, especially the near-room-temperature ferromagnet Fe$_{4}$GeTe$_{2}$, receives a significant attention. Fe$_{4}$GeTe$_{2}$ features a peculiar spin reorientation transition at $T_\mathrm{SR} \sim 110$ K suggesting a non-trivial temperature ev… ▽ More In the quest for two-dimensional conducting materials with high ferromagnetic ordering temperature the new family of the layered Fe$_{n}$GeTe$_{2}$ compounds, especially the near-room-temperature ferromagnet Fe$_{4}$GeTe$_{2}$, receives a significant attention. Fe$_{4}$GeTe$_{2}$ features a peculiar spin reorientation transition at $T_\mathrm{SR} \sim 110$ K suggesting a non-trivial temperature evolution of the magnetic anisotropy (MA) - one of the main contributors to the stabilization of the magnetic order in the low-D systems. An electron spin resonance (ESR) spectroscopic study reported here provides quantitative insights into the unusual magnetic anisotropy of Fe$_{4}$GeTe$_{2}$. At high temperatures the total MA is mostly given by the demagnetization effect with a small contribution of the counteracting intrinsic magnetic anisotropy of an easy-axis type, whose growth below a characteristic temperature $T_{\rm shape} \sim 150$ K renders the sample seemingly isotropic at $T_\mathrm{SR}$. Below one further temperature $T_{\rm d} \sim 50$ K the intrinsic MA becomes even more complex. Importantly, all the characteristic temperatures found in the ESR experiment match those observed in transport measurements, suggesting an inherent coupling between magnetic and electronic degrees of freedom in Fe$_{4}$GeTe$_{2}$. This finding together with the observed signatures of the intrinsic two-dimensionality should facilitate optimization routes for the use of Fe$_{4}$GeTe$_{2}$ in the magneto-electronic devices, potentially even in the monolayer limit. △ Less

Submitted 9 December, 2025; originally announced December 2025.

Journal ref: Adv. Funct. Mater. 34, 2402551 (2024)

WSe2 p-MOSFETs with Nb-Doped WS2 Contacts Deposited using Atomic Layer Deposition

Authors: Shivanshu Mishra, Ruixue Li, Dongjea Seo, Anil Adhikari, Lucas G. Cooper, Rebecca A. Dawley, Ageeth A. Bol, Steven J. Koester

Abstract: WSe2 p-MOSFETs with Nb-doped WS2 contacts formed using atomic layer deposition are demonstrated. The devices are fabricated using a technique that aligns the contact metallization with the Nb-doped WS2 contacts using a selective oxidation process. Devices with source/drain spacing of 0.15 um have on-state current of 103 uA/um at VDS = -1 V at a channel carrier concentration of ~ 7.5 x 1012 cm-2. T… ▽ More WSe2 p-MOSFETs with Nb-doped WS2 contacts formed using atomic layer deposition are demonstrated. The devices are fabricated using a technique that aligns the contact metallization with the Nb-doped WS2 contacts using a selective oxidation process. Devices with source/drain spacing of 0.15 um have on-state current of 103 uA/um at VDS = -1 V at a channel carrier concentration of ~ 7.5 x 1012 cm-2. The results provide a promising CMOS-compatible pathway to create low-resistance contacts to 2D-channel transistors. △ Less

Submitted 24 November, 2025; originally announced November 2025.

Comments: 5 figures, 4 pages

Physical Reinforcement Learning

Authors: Sam Dillavou, Shruti Mishra

Abstract: Digital computers are power-hungry and largely intolerant of damaged components, making them potentially difficult tools for energy-limited autonomous agents in uncertain environments. Recently developed Contrastive Local Learning Networks (CLLNs) - analog networks of self-adjusting nonlinear resistors - are inherently low-power and robust to physical damage, but were constructed to perform superv… ▽ More Digital computers are power-hungry and largely intolerant of damaged components, making them potentially difficult tools for energy-limited autonomous agents in uncertain environments. Recently developed Contrastive Local Learning Networks (CLLNs) - analog networks of self-adjusting nonlinear resistors - are inherently low-power and robust to physical damage, but were constructed to perform supervised learning. In this work we demonstrate success on two simple RL problems using Q-learning adapted for simulated CLLNs. Doing so makes explicit the components (beyond the network being trained) required to enact various tools in the RL toolbox, some of which (policy function and value function) are more natural in this system than others (replay buffer). We discuss assumptions such as the physical safety that digital hardware requires, CLLNs can forgo, and biological systems cannot rely on, and highlight secondary goals that are important in biology and trainable in CLLNs, but make little sense in digital computers. △ Less

Submitted 21 November, 2025; originally announced November 2025.

Comments: 9 pages 4 figures

From LRO to Disorder via QLRO in Spatially Inhomogeneous Polar Flock

Authors: Anish Kumar, Vivek Semwal, Shradha Mishra

Abstract: We study the collective behavior of a polar flock in an inhomogeneous environment in two-dimensions. The inhomogeneity is modelled by introducing regions at random locations on the substrate with higher noise but accessible for the flock to move. Hence inside such regions the particles orientation get randomised. Such inhomogeneities are different from the physical disorder, which obstructs the sp… ▽ More We study the collective behavior of a polar flock in an inhomogeneous environment in two-dimensions. The inhomogeneity is modelled by introducing regions at random locations on the substrate with higher noise but accessible for the flock to move. Hence inside such regions the particles orientation get randomised. Such inhomogeneities are different from the physical disorder, which obstructs the space for the incoming particles. The study focuses on how the phase behavior of polar flock changes by tuning the packing fraction of inhomogeneity. As packing fraction increases, the system crosses over from long-range to quasi long range order and ultimately to a disordered phase, while the order disorder transition for flocking changes from discontinuous to continuous. The resultant phase behavior of polar flock patterns here is comparable to that exhibited in the presence of physical disorder. △ Less

Submitted 14 November, 2025; originally announced November 2025.

Nonadiabatic and anharmonic effects in high-pressure H3S and D3S superconductors

Authors: Shashi B. Mishra, Elena R. Margine

Abstract: Superconductivity in compressed H3S arises from the interplay between high-frequency phonons and a pronounced van Hove singularity near the Fermi level. Using first-principles calculations, we investigate the superconducting properties of H3S and D3S at 160 and 200 GPa, explicitly incorporating anharmonic lattice dynamics and first-order vertex corrections to electron-phonon (e-ph) interactions, t… ▽ More Superconductivity in compressed H3S arises from the interplay between high-frequency phonons and a pronounced van Hove singularity near the Fermi level. Using first-principles calculations, we investigate the superconducting properties of H3S and D3S at 160 and 200 GPa, explicitly incorporating anharmonic lattice dynamics and first-order vertex corrections to electron-phonon (e-ph) interactions, thereby going beyond the Migdal approximation underlying conventional Migdal-Eliashberg theory. We find that both anharmonicity and nonadiabatic vertex corrections suppress the effective e-ph coupling and reduce the superconducting critical temperature (Tc). Calculations performed within the energy-dependent full-bandwidth Eliashberg formalism, including both anharmonic and vertex effects, yield Tc values in close agreement with experimental measurements for D3S at both pressures and for H3S at 200 GPa. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Comments: 10 pages, 5 figures

Comparative study of phonon-limited carrier transport in the Weyl semimetal TaAs family

Authors: Shashi B. Mishra, Zhe Liu, Sabyasachi Tiwari, Feliciano Giustino, Elena R. Margine

Abstract: We present a systematic first-principles study of phonon-limited transport in the TaAs family of Weyl semimetals using the ab initio Boltzmann transport equation. The calculated electrical conductivities show excellent agreement with experimental data for high-quality samples, confirming that transport in these systems is predominantly limited by phonon scattering. Among the four compounds, NbP ac… ▽ More We present a systematic first-principles study of phonon-limited transport in the TaAs family of Weyl semimetals using the ab initio Boltzmann transport equation. The calculated electrical conductivities show excellent agreement with experimental data for high-quality samples, confirming that transport in these systems is predominantly limited by phonon scattering. Among the four compounds, NbP achieves the highest conductivity, governed primarily by its large Fermi velocities that offset its stronger scattering rates. In contrast, TaAs displays the lowest conductivity, linked to reduced carrier pockets and limited carrier velocities. Additionally, NbP conductivity remains largely unaffected by small hole or electron doping, whereas TaAs exhibits pronounced electron-hole asymmetry. NbAs and TaP show intermediate behavior, reflecting their Fermi surface topologies and scattering phase space. These findings provide microscopic insight into the transport mechanisms of the TaAs family and emphasize the critical role of phonons, doping, and carrier dynamics in shaping their electronic response. △ Less

Submitted 15 October, 2025; originally announced October 2025.

Comments: 8 pages, 6 figures

DiffCrysGen: A Generative Diffusion Model for Accelerated Design of Inorganic Crystalline Materials

Authors: Sourav Mal, Nehad Ahmed, Junaid Jami, Subhankar Mishra, Prasenjit Sen

Abstract: Efficient exploration of the vast chemical space is a fundamental challenge in materials design and discovery, particularly for designing functional inorganic crystalline materials with targeted properties. Diffusion-based generative models have emerged as a powerful route, but most existing approaches require domain-specific constraints and separate diffusion processes for atom types, atomic posi… ▽ More Efficient exploration of the vast chemical space is a fundamental challenge in materials design and discovery, particularly for designing functional inorganic crystalline materials with targeted properties. Diffusion-based generative models have emerged as a powerful route, but most existing approaches require domain-specific constraints and separate diffusion processes for atom types, atomic positions, and lattice parameters, adding complexity and limiting efficiency. Here, we present DiffCrysGen, a fully data-driven, score-based diffusion model that generates complete crystal structures in a single, end-to-end diffusion process. This unified framework simplifies the model architecture and accelerates sampling by two to three orders of magnitude compared to existing methods without compromising chemical and structural diversity of the generated materials. In order to demonstrate the efficacy of DiffCrysGen in generating valid and useful materials, using density functional theory (DFT), we validate a number of newly generated rare earth-free magnetic materials that are energetically and dynamically stable, and are potentially synthesizable. These include ferromagnets with high saturation magnetization and large magnetocrystalline anisotropy, as also metallic antiferromagnets. These results establish DiffCrysGen as a general platform for accelerated design of functional materials. △ Less

Submitted 19 March, 2026; v1 submitted 14 October, 2025; originally announced October 2025.

Comments: v2: Updated title and author list; manuscript revised with supplementary information included. Total 66 pages, 11 figures

Field-induced magnetic phases in the Kitaev candidate Na$_3$Co$_2$SbO$_6$

Authors: Kranthi Kumar Bestha, Manaswini Sahoo, Niccolò Francini, Robert Kluge, Ryan Morrow, Andrey Maljuk, Sabine Wurmehl, Sven Luther, Yurii Skourski, Hannes Kühne, Swarnamayee Mishra, Jochen Geck, Manuel Brando, Bernd Büchner, Laura T. Corredor, Lukas Janssen, Anja U. B. Wolter

Abstract: We report a rich anisotropic magnetic phase diagram of Na$_3$Co$_2$SbO$_6$, a previously proposed cobaltate Kitaev candidate, based on field- and temperature-dependent magnetization, specific heat, and magnetocaloric effect studies. At low temperatures, our experiments uncover a low-lying $j_{\textrm{eff}} = \frac{1}{2}$ state with an antiferromagnetic ground state and pronounced in-plane versus o… ▽ More We report a rich anisotropic magnetic phase diagram of Na$_3$Co$_2$SbO$_6$, a previously proposed cobaltate Kitaev candidate, based on field- and temperature-dependent magnetization, specific heat, and magnetocaloric effect studies. At low temperatures, our experiments uncover a low-lying $j_{\textrm{eff}} = \frac{1}{2}$ state with an antiferromagnetic ground state and pronounced in-plane versus out-of-plane anisotropy. The experimentally identified magnetic phases are theoretically characterized through classical Monte Carlo simulations within an extended Kitaev-Heisenberg model with additional ring exchange interactions. The resulting phase diagram reveals a variety of exotic field-induced magnetic phases, including double-$\textbf{q}$, $\frac{1}{3}$-AFM, zigzag, and vortex phases. △ Less

Submitted 10 October, 2025; originally announced October 2025.

Journal ref: Phys. Rev. B 113, L100412 (2026)

Quantum oscillations and anisotropic magnetoresistance in the quasi-two-dimensional Dirac nodal line superconductor $\mathrm{YbSb_2}$

Authors: Yuxiang Gao, Kevin Allen, Rose Albu Mustaf, Yichen Zhang, Sanu Mishra, Christopher Lane, Marta Zonno, Sergey Gorovikov, Jian-Xin Zhu, Ming Yi, Emilia Morosan

Abstract: Recent interest in quantum materials has focused on systems exhibiting both superconductivity and non-trivial band topology as material candidates to realize topological or unconventional superconducting states. So far, superconductivity in most topological materials has been identified as type II. In this work, we present magnetotransport studies on the quasi-two-dimensional type I superconductor… ▽ More Recent interest in quantum materials has focused on systems exhibiting both superconductivity and non-trivial band topology as material candidates to realize topological or unconventional superconducting states. So far, superconductivity in most topological materials has been identified as type II. In this work, we present magnetotransport studies on the quasi-two-dimensional type I superconductor $\mathrm{YbSb_2}$. Combined ab initio DFT calculations and quantum oscillation measurements confirm that $\mathrm{YbSb_2}$ is a Dirac nodal line semimetal in the normal state. The complex Fermi surface morphology is evidenced by the non-monotonic angular dependence of both the quantum oscillation amplitude and the magnetoresistance. Our results establish $\mathrm{YbSb_2}$ as a candidate material platform for exploring the interplay between band topology and superconductivity. △ Less

Submitted 6 October, 2025; originally announced October 2025.

Comments: 9 pages, 8 figures

Fermi surface and Berry phase analysis for Dirac nodal line semimetals: cautionary tale to SrGa$_2$ and BaGa$_2$

Authors: Yuxiang Gao, Yichen Zhang, Shiming Lei, Neil Harrison, Mun Keat Chan, Jonathan D. Denlinger, Sergey Gorovikov, Sanu Mishra, Yan Sun, Ming Yi, Emilia Morosan

Abstract: A Berry phase of odd multiples of $π$ inferred from quantum oscillations (QOs) has often been treated as evidence for nontrivial reciprocal space topology. However, disentangling the Berry phase values from the Zeeman effect and the orbital magnetic moment is often challenging. In centrosymmetric compounds, the case is simpler as the orbital magnetic moment contribution is negligible. Although the… ▽ More A Berry phase of odd multiples of $π$ inferred from quantum oscillations (QOs) has often been treated as evidence for nontrivial reciprocal space topology. However, disentangling the Berry phase values from the Zeeman effect and the orbital magnetic moment is often challenging. In centrosymmetric compounds, the case is simpler as the orbital magnetic moment contribution is negligible. Although the Zeeman effect can be significant, it is usually overlooked in most studies of QOs in centrosymmetric compounds. Here, we present a detailed study on the non-magnetic centrosymmetric $\mathrm{SrGa_2}$ and $\mathrm{BaGa_2}$, which are predicted to be Dirac nodal line semimetals (DNLSs) based on density functional theory (DFT) calculations. Evidence of the nontrivial topology is found in magnetotransport measurements. The Fermi surface topology and band structure are carefully studied through a combination of angle-dependent QOs, angle-resolved photoemission spectroscopy (ARPES), and DFT calculations, where the nodal line is observed in the vicinity of the Fermi level. Strong de Haas-van Alphen fundamental oscillations associated with higher harmonics are observed in both compounds, which are well-fitted by the Lifshitz-Kosevich (LK) formula. However, even with the inclusion of higher harmonics in the fitting, we found that the Berry phases cannot be unambiguously determined when the Zeeman effect is included. We revisit the LK formula and analyze the phenomena and outcomes that were associated with the Zeeman effect in previous studies. Our experimental results confirm that $\mathrm{SrGa_2}$ and $\mathrm{BaGa_2}$ are Dirac nodal line semimetals. Additionally, we highlight the often overlooked role of spin-damping terms in Berry phase analysis. △ Less

Submitted 6 October, 2025; originally announced October 2025.

Comments: 15 pages, 13 figures

$Δ_T$ Noise as a Robust Diagnostic for Chiral, Helical and Trivial Edge Modes

Authors: Sachiraj Mishra, Colin Benjamin

Abstract: In this article, we demonstrate that $Δ_T$ noise provides a sensitive, practical probe for distinguishing chiral edge modes from topological helical and trivial (non-topological) helical edge transport. Measured under zero-current conditions, $Δ_T$ noise reveals contrasts that conventional conductance measurements typically miss. Crucially, $Δ_T$ noise requires no external energy input in the form… ▽ More In this article, we demonstrate that $Δ_T$ noise provides a sensitive, practical probe for distinguishing chiral edge modes from topological helical and trivial (non-topological) helical edge transport. Measured under zero-current conditions, $Δ_T$ noise reveals contrasts that conventional conductance measurements typically miss. Crucially, $Δ_T$ noise requires no external energy input in the form of an applied voltage bias, yet encodes the same intrinsic information that shot noise yields in the zero-temperature, finite-bias limit, without the distorting effects of Joule heating. This absence of bias-induced heating makes $Δ_T$ noise both more precise and more reliable than conventional shot-noise approaches. △ Less

Submitted 5 July, 2026; v1 submitted 20 September, 2025; originally announced September 2025.

Comments: 25 pages, 11 figures, 2 Tables; accepted for publication in J. Phys.: Condens. Matter

Journal ref: J. Phys.: Condens. Matter 38, 275901 (2026)

Skeletal editing by tip-induced chemistry

Authors: Shantanu Mishra, Valentina Malave, Rasmus Svensson, Henrik Grönbeck, Florian Albrecht, Diego Peña, Leo Gross

Abstract: Skeletal editing of cyclic molecules has garnered considerable attention in the context of drug discovery and green chemistry, with notable examples in solution-phase synthesis. Here, we extend the scope of skeletal editing to the single-molecule scale. We demonstrate tip-induced oxygen deletion and ring contraction of an oxygen-containing seven-membered ring on bilayer NaCl films to generate mole… ▽ More Skeletal editing of cyclic molecules has garnered considerable attention in the context of drug discovery and green chemistry, with notable examples in solution-phase synthesis. Here, we extend the scope of skeletal editing to the single-molecule scale. We demonstrate tip-induced oxygen deletion and ring contraction of an oxygen-containing seven-membered ring on bilayer NaCl films to generate molecules containing the perylene skeleton. The products were identified and characterized by atomic force and scanning tunneling microscopies, which provided access to bond-resolved molecular structures and orbital densities. Insights into the reaction mechanisms were obtained by density functional theory calculations. Our work expands the toolbox of tip-induced chemistry for single-molecule synthesis. △ Less

Submitted 15 September, 2025; originally announced September 2025.

Comments: Manuscript: 6 pages and 4 figures; Supporting Information: 18 pages, 21 figures and 1 table

Electric-field Control of Giant Ferronics

Authors: Baolong Zhang, Ruihuan Duan, Sobhan Subhra Mishra, Sambhu Jana, Jonghyeon Kim, Thomas Tan Caiwei, Yi Ji Tan, Wenhao Wang, Pang Teng Chen Ietro, Zheng Liu, Ranjan Singh

Abstract: Ferrons are quantum excitations of electric polarization in ferroelectrics and electric analogues of magnons but have lacked direct experimental verification at room temperature. We harness the coupling of soft phonons and ferroelectric order in layered NbOX2 (X = I, Br, Cl) to generate, detect, and control giant ferrons, creating a new class of ultralow-power, chip-scale terahertz (THz) sources.… ▽ More Ferrons are quantum excitations of electric polarization in ferroelectrics and electric analogues of magnons but have lacked direct experimental verification at room temperature. We harness the coupling of soft phonons and ferroelectric order in layered NbOX2 (X = I, Br, Cl) to generate, detect, and control giant ferrons, creating a new class of ultralow-power, chip-scale terahertz (THz) sources. Multiple ferron modes produce intense, narrowband THz emission with quality factors up to 228 and radiation efficiencies up to five orders of magnitude greater than state of the art semiconductor emitters. Resonant excitation of a high-Q ferron mode achieves efficiencies two orders of magnitude higher than intense lithium niobate THz sources. We further demonstrate direct, non-volatile electric-field control of ferron oscillations. These findings provide evidence for multiple ferrons and establish Ferronics as a foundational platform for light- and field-driven control of quantum order, with broad impact on ultrafast electronics, photonics, quantum technologies, and next-generation wireless communication. △ Less

Submitted 7 September, 2025; originally announced September 2025.

Comments: 15 pages, 5 figures

Analytical Theory of Chiral Active Particle Transport in a Fluctuating Density Field

Authors: Jayam Joshi, Abhra Puitandy, Shradha Mishra

Abstract: We develop a closed-form analytical theory for the transport of a chiral active Brownian particle in three dimensions, moving through a fluctuating local density field that models steric and dynamical interactions in a dense active medium. The density field is modeled as an Ornstein--Uhlenbeck process with finite correlation time $τ$ and fluctuation strength $σ_ρ^2$, capturing both spatial fluctua… ▽ More We develop a closed-form analytical theory for the transport of a chiral active Brownian particle in three dimensions, moving through a fluctuating local density field that models steric and dynamical interactions in a dense active medium. The density field is modeled as an Ornstein--Uhlenbeck process with finite correlation time $τ$ and fluctuation strength $σ_ρ^2$, capturing both spatial fluctuations and temporal memory. Within this framework, we derive exact expressions for the mean-squared displacement and time-dependent diffusivity, revealing how chirality and density coupling jointly renormalise orientational persistence and generate nontrivial dynamical crossovers. The theory predicts: (i) anomalously high initial diffusivity for particles starting in locally denser regions, arising from a transient active drift driven by local swim-pressure gradients; (ii) a finite crossover time $t_c$ for homogenising density inhomogeneities, with a transient dependence of the dynamics on the initial local density environment which arises from the non-equilibrium evolution of density fluctuations and does not persist when averaging over stationary initial conditions ($ρ_0 = ρ_\infty$) ; (iii) a non-monotonic $t_c(Ω)$ with a global minimum at intermediate chirality, and a three-regime suppression of long-time diffusivity $D_\infty(Ω)$, consistent with micro-clustered phases observed in simulations; and (iv) a resonance-like peak in the early-time oscillatory strength of the mean-squared displacement at an optimal chirality $Ω^*$, set by the interplay of orientational diffusion, density-field decorrelation, and imposed rotation. The framework captures the qualitative dependence of $D_\infty$ on $Pe$ and $Ω$, {where Pe denotes the Péclet number}, while uncovering chirality-dependent transport features in active matter. △ Less

Submitted 12 June, 2026; v1 submitted 21 August, 2025; originally announced August 2025.