arXiv subjects

Reza Asgari

Publications and source records attributed to Reza Asgari.

At least 19 recordsLinked to original sources

arXiv2026

Time-dependent Berry curvature and quantum metric of Floquet-Bloch states

The quantum geometry of Bloch bands, characterized by the Berry curvature and the quantum metric, underpins a wide range of linear and nonlinear responses in static systems. Here, we extend this framework to periodically driven (Floquet) systems by introducing a time-dependent Berry curvature and quantum metric defined directly in the Floquet-Bloch basis. We derive optical sum rules that relate the Fourier components of these geometric quantities to the optical conductivity and demonstrate that, under ideal Floquet-band occupations, the first-order DC Hall and longitudinal responses at harmonic frequencies vanish identically. We further introduce a mixed Berry curvature involving time and momentum derivatives, which gives rise to a non-adiabatic quantized charge-pumping mechanism that occurs naturally during each driving period without requiring adiabatic evolution. In addition, we identify the time-domain quantum metric as a measure of the energy fluctuations of a Floquet band and interpret its mixed components as quantifying polarization-energy correlations. A comprehensive symmetry analysis reveals how time-reversal, sublattice (chiral), particle-hole, inversion, rotational, and reflection symmetries constrain the time-dependent quantum geometric tensor and its associated topological invariant. Numerical simulations of the Rudner-Lindner-Berg-Levin model and a fully symmetric Floquet model confirm the analytical predictions. These results establish the time-dependent quantum geometric tensor as a unified framework for describing the geometric, topological, and dynamical properties of periodically driven quantum systems, with direct implications for optical spectroscopy, quantum transport, and topological charge-pumping experiments.

cond-mat.mes-hall↗

arXiv2026

Nonlinear Hall effect in Floquet-driven monolayer 1T$'$-MoS$_2$

We study the nonlinear Hall effect in Floquet-driven monolayer $1T'$-MoS$_2$, a low-symmetry quantum spin Hall material whose tilted Dirac bands sustain an intrinsic Berry-curvature dipole without the need for strain or trigonal warping. We show that off-resonant circularly polarized light offers a way to control both the sign and the magnitude of the nonlinear Hall response through optically induced topological phase transitions using a Floquet effective Hamiltonian and nonlinear semiclassical transport theory. We show that the anisotropic crystal symmetry enforces a selection rule in which the Berry-curvature dipole elements satisfy $D_x\equiv0$, while a finite $D_y$ originates from the intrinsic band tilt. The Berry curvature is recreated in momentum space as the Floquet drive successively inverts individual spin-valley sectors, resulting in an identical sign reversal of the nonlinear Hall conductivity and the Berry-curvature dipole at each bulk gap closing. In contrast, tuning the band tilt modifies only the magnitude of the response without changing its sign, establishing the observed sign reversal as an unambiguous transport signature of genuine Floquet topological phase transitions. We further show that the nonlinear Hall response can be controlled by the driving strength, perpendicular electric field, Fermi energy, and temperature, providing multiple experimental knobs for observation. Our findings establish the sign of the nonlinear Hall response as a universal transport fingerprint of Floquet-engineered topology and point to monolayer $1T'$-MoS$_2$ as a viable platform for all-electrical detection of nonequilibrium topological phases.

cond-mat.mes-hall↗

arXiv2026

Intrinsic Topological Control of the Orbital Hall Effect in Buckled Dirac Materials

We study the orbital Hall response in buckled two-dimensional Dirac materials using a unified framework that includes an antiferromagnetic exchange field, a perpendicular electric field, and intrinsic spin-orbit coupling. We show that the orbital Hall conductivity is considerably boosted around band-inversion points and shows different signatures across multiple electronic phases using a low-energy massive Dirac model in conjunction with Berry-curvature-based linear response theory. We find a series of quantum spin Hall, valley Hall, and anomalous Hall regimes by methodically adjusting external fields, and demonstrate how the evolution of the orbital response is controlled by the redistribution of Berry curvature between spin and valley sectors. We examine the impacts of finite temperature in more detail and find that although the response s size is suppressed by thermal broadening, the distinctive phase-dependent features remain robust. Our findings demonstrate that orbital Hall conductivity offers a sensitive band topology probe in Dirac systems and emphasize buckled two-dimensional materials as a flexible platform for engineering tunable orbital currents for orbitronic applications.

cond-mat.mes-hall↗

arXiv2026

Light-Induced Topological Phase Transitions and Anomalous Thermal Transport in d-Wave Altermagnets

We study intrinsic thermal transport and Floquet-engineered topology in a two-dimensional d wave altermagnetic topological insulator powered by linearly polarized light. We analyze the anomalous Hall, Nernst, and thermal Hall conductivities, as well as their spin-resolved equivalents, and develop closed-form formulas for the Berry curvature using an analytically calculated high-frequency effective Hamiltonian. We demonstrate that linearly polarized light, in contrast to conventional antiferromagnets, breaks the symmetry connecting spin sectors in altermagnets, allowing a series of spin-selective topological phase transitions from a quantum spin Hall state to a spin-polarized Chern insulator and finally to a trivial phase. The Nernst response shows substantial thermal activation and significant sensitivity to the gap size in the Chern domain, but both the electrical and thermal Hall responses become quantized and meet the anomalous Wiedemann Franz law. Every anomalous transport coefficient exhibits a distinctive d wave dependence on the polarization angle, reversing sign under orthogonal rotation and vanishing at symmetry-restoring directions. Our findings show a path to all-optical regulation of topological and caloritronic responses beyond traditional magnetic systems and establish thermal transport as a sensitive probe of altermagnetic order.

cond-mat.mes-hall↗

arXiv2026

Floquet-driven thermal transport in topological Haldane lattice systems

In this paper, we employ a modified Haldane lattice model to investigate the light-driven, spin- and valley-dependent anomalous Nernst effect in two-dimensional hexagonal topological systems. We demonstrate that two-dimensional buckled materials exhibit a hierarchy of electrically and optically tunable topological phases when subjected to off-resonant circularly polarized light in the presence of intrinsic spin-orbit coupling and a staggered sublattice potential. Within a Berry-curvature-driven transport framework, we systematically analyze charge-, spin-, and valley-resolved anomalous Nernst responses and identify their correspondence with distinct topological regimes. A finite charge Nernst conductivity arises under optical driving combined with spin-orbit coupling, whereas the generation of a pure valley Nernst current requires the simultaneous presence of sublattice asymmetry and off-resonant light. Substrate-induced inversion asymmetry further enables thermally driven valley currents with tunable magnitude and sign. We find that single-spin and single-valley Nernst responses occur in selected insulating and metallic phases, while the valley Nernst signal is suppressed in spin-polarized and anomalous quantum Hall phases. Extending our analysis to monolayer MoS$_2$, we show that strong spin-orbit coupling and broken inversion symmetry allow fully spin- and valley-polarized Nernst currents over a broad energy window. The temperature dependence of the Nernst response exhibits characteristic signatures of topological phase transitions, establishing the anomalous Nernst effect as a sensitive probe of field-engineered band topology in two-dimensional Dirac materials.

cond-mat.other↗

arXiv2026

Interlayer Coupling and Floquet-Driven Topological Phases in Bilayer Haldane Lattices

We investigate Floquet-driven topological phase transitions in an AB-stacked bilayer Haldane lattice with tunable intralayer hopping anisotropy. By combining interlayer hybridization, Haldane flux, and off-resonant circularly polarized light, we obtain controlled transitions among Dirac, semi-Dirac, and higher-Chern insulating phases. As the hopping anisotropy increases, the two inequivalent Dirac points move toward each other and merge at the Brillouin-zone $\mathbf{M}$ point, where a semi-Dirac dispersion emerges with linear and quadratic momentum dependence along orthogonal directions. In this regime, competition between the intrinsic Haldane mass and the Floquet-induced mass drives a sequence of sharp topological transitions with Chern numbers $C=0,\pm1,\pm2$. We further show that interlayer coupling qualitatively reshapes the Floquet band topology by inducing helicity-dependent and valley-selective band inversions at the K and K$'$ points, thereby stabilizing higher-Chern phases in the valence bands. These changes are accompanied by redistribution of the Berry curvature, bulk gap closings, and the collapse or sign reversal of quantized anomalous Hall plateaus. As the system approaches the semi-Dirac limit, the topological phase space narrows and disappears at the critical merger point, beyond which the system becomes topologically trivial even when it remains gapped. Overall, the bilayer geometry broadens the scope of Floquet topological control by enabling dynamically tunable higher-Chern phases and valley-dependent Hall responses governed by interlayer coupling and light helicity.

cond-mat.mes-hall↗

arXiv2025

Interplay of Rashba and Dresselhaus Spin-Orbit Couplings on the Stability of Topological FFLO Phases in 1D Fermi Gases

We investigate the stabilization of topological Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases, with a specific emphasis on the intraband FFLO phase, in a one-dimensional (1D) Fermi gas subjected to an external magnetic field. This research highlights the crucial role of the interplay between Rashba spin-orbit coupling (RSOC) and Dresselhaus spin-orbit coupling (DSOC). Employing a Fermi-Hubbard model alongside the density matrix renormalization group (DMRG) method, we examine the combined effects of RSOC and DSOC on these exotic superfluid phases, taking into account attractive fermionic interactions. Our principal finding reveals that while RSOC primarily stabilizes conventional zero-momentum pairing, DSOC performs a distinct and crucial role in selectively stabilizing the intraband FFLO phase. This stabilization is achieved by enhancing spin polarization within a single helicity band and suppressing interband coherence, thereby facilitating the formation of finite-momentum FFLO pairs within the same band and resulting in the emergence of a topologically nontrivial superfluid. This targeted control of intraband FFLO pairing paves the way for new strategies in the manipulation of superfluid phases in spin-orbit coupled systems and offers essential insights for experimental realizations in ultracold atomic gases, with implications for topological quantum computing and Majorana fermions.

cond-mat.quant-gas↗

arXiv2025

Nonlinear Optical Response in Pseudo-Hermitian Systems at Steady State

We establish a steady-state theory for nonlinear optical conductivity in pseudo-Hermitian systems. We derive compact formulas for the first and second order conductivity tensors in both the velocity and length gauges and prove their exact equivalence through generalized sum rules and Berry connection identities by formulating the nonlinear response in terms of a biorthogonal density matrix. Utilizing the formalism on parity-time symmetric two-level systems reveals nonlinear phenomena that are not present in Hermitian systems, such as extra terms in the conductivity, corrections to the velocity operator, photocurrent, and resonance structures with higher-order poles at one-photon transitions. These features yield qualitatively distinct harmonic generation responses like real second-order conductivities and nonzero DC limits. These results provide new insights into nonlinear light-matter interactions in active media characterized by balanced gain and loss, with implications for non-Hermitian photonics, dissipative topological systems, and quantum devices designed with engineered dissipation.

cond-mat.mes-hall↗

arXiv2025

Current-induced spin-orbit torque on the surface of a transition metal dichalcogenide connected to a two-dimensional ferromagnet CrI$_3$: Effects of twisting and gating

Motivated by recent progress in employing two key classes of two-dimensional materials-topological insulators and transition-metal dichalcogenides (TMDCs)-as spin sources for generating spin-orbit torque (SOT), we investigate current-induced spin polarization and the resulting SOT in bilayers composed of a TMDC (WSe$_2$ or MoSe$_2$) and ferromagnetic chromium iodide (CrI$_3$), beyond the linear response regime. Using the steady-state Boltzmann equation, we find that intra-band transitions yield a strong field-like torque on the CrI$_3$ layer, while inter-band transitions give rise to a comparatively weaker damping-like torque in the WSe$_2$/CrI$_3$ system. Remarkably, the damping-like component is enhanced by up to three orders of magnitude in n-doped MoSe$_2$, reaching a strength comparable to the field-like torque, which itself is an order of magnitude larger than that in the WSe$_2$-based bilayer. Both torque components exhibit strong asymmetry between n-type and p-type doping in WSe$_2$ and MoSe$_2$ systems. Furthermore, we demonstrate that the twist angle plays a crucial role: depending on the TMDC and chemical potential, twisting can reverse the sign of the SOT and significantly modulate its magnitude. Finally, we show that a transverse gate electric field enables substantial tunability of the SOT, by nearly one order of magnitude, and induces a sign reversal at a twist angle of $10.16^{\circ}$.

cond-mat.mes-hall↗

arXiv2025

Quantum magnetotransport in monolayer $\mathrm{Pt_{2}HgSe_{3}}$

We present a theoretical framework to investigate quantum magnetotransport in monolayer jacutingaite, focusing on its response to external electric fields and off-resonant circularly polarized laser irradiation. Our analysis reveals a sequence of topological phase transitions triggered by tuning these external parameters. We find that the zeroth LL exhibits spin- and valley-polarized splitting, leading to four distinct peaks in the DOSs for the $K$ and $K'$ valleys. Using the Kubo formalism, we calculate both longitudinal and Hall magneto-optical conductivities based on the Kane-Mele model. Our results demonstrate that external electric, magnetic, and off-resonant optical fields can control these conductivities. These findings highlight monolayer jacutingaite as a highly tunable platform with strong potential for future applications in photonics, optoelectronics, and topological quantum devices.

cond-mat.mes-hall↗

arXiv2025

Heat Dissipation and Thermoelectric Performance of InSe-Based Monolayers: A Monte Carlo Simulation Study

Using nonequilibrium Monte Carlo simulations of the phonon Boltzmann transport equation, we study transient heat transfer in five indium-based two-dimensional monolayers: Janus monolayers In$_2$SeTe and In$_2$SSe, pristine InSe, and InSe under 4$\%$ and 6$\%$ tensile strain. In this work, the potential of these materials for energy conversion in thermoelectric generators and hotspot control in metal-oxide-semiconductor field-effect transistors is investigated. A promising option for an effective heat dissipation and enhanced transistor reliability is found to be a strained InSe, which shows the lowest peak temperature during the heating among the studied materials. On the other hand, with a high Seebeck coefficient, low thermal conductivity, and an improved figure of merit, the Janus In$_2$SeTe monolayer, compensates for its increased phonon scattering to reach the maximum temperature, making it a potent thermoelectric material. Our findings emphasis the importance of strain engineering and structural asymmetry in tuning phonon transport, enabling material optimization for next-generation nanoelectronic and energy-harvesting devices.

physics.app-ph↗

arXiv2025

Velocity gauge formulation of nonlinear optical response in Floquet-driven systems

Using the velocity gauge formalism, we develop a theoretical framework for computing the nonlinear optical responses of time-periodic quantum systems. This approach complements the length gauge formulation and offers distinct advantages in both numerical and analytical treatments, particularly for atomic and solid-state systems with well-defined momentum-space structures. By applying our framework to the Rabi model, we derive numerical solutions in the velocity gauge and compare them with the length gauge, demonstrating full agreement between the two formulations. Our findings reveal rich optical phenomena, including photon-assisted transitions, frequency mixing effects, and emergent Floquet-induced photocurrents that are absent in static systems. We demonstrate that nonlinear responses in Floquet-driven systems exhibit resonances at integer multiples of the driving frequency, providing insights into ultrafast spectroscopy and Floquet engineering of quantum materials. The present formulation establishes a bridge between theoretical models and experimental observations in driven quantum systems, with potential applications in quantum optics, photonics, and next-generation optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Comparing the Extrinsic Orbital Hall Effect in Centrosymmetric and Noncentrosymmetric Systems: Insights from Bilayer Transition Metal Dichalcogenides

We investigate both intrinsic and extrinsic orbital Hall effects (OHE) in bilayer transi tion metal dichalcogenides (TMDs) in the presence of short-range disorder using quan tum kinetic theory. Bilayer TMDs provide an ideal platform to study the effects of inversion symmetry breaking on transport properties due to their unique structural and electronic characteristics. While bilayer TMDs are naturally inversion symmetric, ap plying a finite gate voltage to create a bias between the layers effectively breaks this symmetry. Our findings reveal that slightly away from the band edges, the extrinsic OHE eventually becomes the dominant contribution in both inversion-symmetric and asymmetric cases, with its prominence increasing significantly as a function of Fermi energy. Furthermore, we demonstrate that breaking inversion symmetry greatly en hances the extrinsic OHE. This enhancement arises from the fundamentally distinct behavior of orbital angular momentum (OAM) in centrosymmetric systems, where in traband components vanish due to symmetry constraints. As a result, in centrosym metric systems, only the off-diagonal components of the density matrix contribute to the extrinsic OHE. In contrast, in noncentrosymmetric systems, both diagonal and off diagonal components play a role. Our study suggests that in experimentally relevant highly doped systems, the OHE becomes predominantly extrinsic in both centrosym metric and noncentrosymmetric although the contribution is much more pronounced in the latter. Importantly, we infer that even a weakly breaking of inversion symmetry can lead to a dramatic enhancement of the OHE, a finding with significant implications for experimental investigations.

cond-mat.mes-hall↗

arXiv2024

Dynamical nonlinear optical response in time-periodic quantum systems

We present a comprehensive theoretical framework for calculating the linear and nonlinear optical responses of time-periodic quantum systems. Using density matrix evolution in the Floquet basis and adopting the length gauge, our approach incorporates both interband and intraband contributions of the position operator, enabling detailed insights into photon-assisted transitions and their associated optical phenomena. Notably, we identify a divergent ac response to dc fields in Floquet systems, reminiscent of a Drude peak at finite frequencies. This framework generalizes to optical tensor conductivity calculations at arbitrary perturbation orders and captures various DC photocurrents, including shift current, injection current, and Berry dipole contributions, under specific limits. To demonstrate the versatility of our method, we compute linear and nonlinear optical conductivities for one- and two-dimensional systems, revealing phenomena such as band inversions, j-photon-assisted transitions, and high harmonic generation. These results highlight the interplay between periodic driving and nonlinear optical effects, offering different avenues for exploring dynamical topological properties and their applications in ultrafast spintronics, optoelectronics, and strongly correlated systems. Our findings provide a robust platform for analyzing the complex optical behavior of driven quantum systems and guiding experimental investigations in this rapidly evolving field.

cond-mat.mtrl-sci↗

arXiv2024

Enhanced Brewster Angle Shift in Doped Graphene via the Fizeau Drag Effect

We derive the general Fresnel coefficients for reflection by incorporating the Fizeau drag effect in doped graphene, which arises from the unique behavior of its massless Dirac electrons. Using the standard Maxwell equations and constitutive relations, we analyze the influence of this relativistic phenomenon on the optical properties of doped graphene. Our study focuses on the angular shift of Brewster's angle in a structure where monolayer graphene is sandwiched between two static dielectric media. Our findings reveal that the presence of the Fizeau drag effect significantly enhances the Brewster angle shift, leading to substantial modifications in the optical characteristics of the graphene channel, including notable alterations in the reflectance spectrum. We demonstrate that this angular shift can be further amplified by increasing the drift velocities and charge densities of the electrons in graphene, offering a tunable mechanism for controlling optical behavior in graphene-based systems. The findings of this work have significant implications for the design and development of planar photonic devices that take advantage of the optical characteristics of graphene. This breakthrough creates new opportunities for the use of graphene in sophisticated photonic technologies, where exact control over the interactions between light and matter is essential.

cond-mat.mes-hall↗

arXiv2024

Photonic spin Hall effect in Haldane model materials

The photonic spin Hall effect of light beams reflected from the surfaces of various two-dimensional hexagonal crystalline structures, considering their associated time-reversal $\mathcal{T}$ and inversion $\mathcal{I}$ symmetries, is investigated. Employing the Haldane model with tunable parameters as a generic model, we examine the longitudinal and transverse spin-separations of the reflected beam in both topological non-trivial and trivial systems. The study reveals that the sign switching of the PSHE in these materials is attributed to the non-trivial and trivial topology. By manipulating the interplay between spin-orbit coupling and external electric fields, we demonstrate topological phase transitions in buckled Xene monolayer materials through the photonic spin Hall effect. Different behaviors of the photonic spin Hall effect are observed in various topological phases within these materials. Additionally, we explore the reflected spin and valley-polarized spatial shifts in monolayer transition metal dichalcogenides. The photonic spin Hall effect in buckled Xene monolayer materials and transition metal dichalcogenides is highly influenced by the spin and valley degrees of freedom of charge carriers, offering a promising avenue to explore spintronics and valleytronics in these hexagonal materials. We propose that the photonic spin Hall effect in Haldane materials can serve as a metrological tool for optical parameter characterization and as a promising method for determining Chern numbers and topological phase transitions through direct optical weak measurement techniques.

cond-mat.mes-hall↗

arXiv2024

Spatio-spectral control of spontaneous emission

We propose a scheme aimed at achieving spatio-spectral control over spontaneous emission within a four-level atom-light coupling system interacting with optical vortices carrying orbital angular momentum (OAM). The atom comprises a ground level and two excited states coupled with two laser fields, forming a V subsystem where the upper states exclusively decay to a common fourth state via two channels. By investigating various initial states of the atom and considering the presence or absence of quantum interference in spontaneous emission channels, we analyze how the characteristics of the OAM-carrying vortex beam imprint onto the emission spectrum. The interplay between the optical vortex and the quantum system, including its environment modes, induces a wide variety of spatio-spectral behaviour, including two-dimensional spectral-peak narrowing, spectralpeak enhancement, spectral-peak suppression, and spontaneous emission reduction or quenching in the spatial azimuthal plane. Our findings shed light on the dynamics of atom-vortex beam light interactions and offer insights into the manipulation of emission properties at the quantum level.

quant-ph↗

arXiv2024

Anomalous Lifetime of Quasiparticles in Fermi Liquids as a Precursor of the Density-Wave Instability

We analytically study the inelastic lifetime of quasiparticles due to particle-particle interactions in a three-dimensional Fermi liquid approaching a density-wave instability. Using the G$_0$W approximation, we find that the softening of the dielectric function significantly enhances the quasiparticle decay rate near the instability. While the zero-temperature quasiparticle lifetime at the Fermi surface generally follows a $|\varepsilon_k-\varepsilon_{\rm F}|^{-α}$ divergence with $α=2$, we observe $α=0.5$ at the instability point and $α=1$ within the density-wave phase. Moreover, we demonstrate that the renormalization constant $Z$ is substantially suppressed as the instability is approached, enhancing the effective mass. We extend our analysis to ultra-cold Rydberg-dressed Fermi liquids, where the soft-core interactions promote density-wave instability, and find that our numerical G$_0$W results are in excellent agreement with our analytic predictions for quasiparticle lifetime, renormalization constant, and effective mass.

cond-mat.str-el↗