arXiv subjects

Gao Xianlong

Publications and source records attributed to Gao Xianlong.

At least 19 recordsLinked to original sources

arXiv2026

Floquet-spin-orbit compensation and flat- and quadratic-band contact in the $α$-$T_3$ lattice

We investigate Floquet--spin-orbit compensation in the three-band $α$-$T_3$ system, which interpolates between graphene at $α=0$ and the dice lattice at $α=1$. By tuning the interplay between an off-resonant circularly polarized optical field and intrinsic spin--orbit coupling, we identify three distinct pairwise band-degeneracy conditions in the quasienergy spectrum: (i) valley--spin degeneracy, (ii) spin--band degeneracy, and (iii) flat--dispersive band degeneracy. The flat band is not an artifact of a two-band reduction but rather an exact property of the continuum Hamiltonian at this compensation point, where the complete three-band Hamiltonian supports a momentum-independent dark state. A winding-two low-energy Hamiltonian and a finite-momentum Berry-curvature maximum, whose radius scales as the square root of the detuning, emerge from detuning this contact. We further show that the intrinsic transverse thermoelectric response encodes these spectrum patterns. The flat- and quadratic-band degeneracy can be predicted for $0<α<1/2$ because the two response scales linked to the linear contacts have a monotonic ratio independent of the common spin--orbit energy scale. This allows an inverse determination of $α$ and of the common spectral scale. The analytical results are confirmed by full three-band Kubo calculations, which also define the regime in which this inverse characterization is still observable. These results connect an experimentally accessible, Berry-curvature-sensitive thermoelectric response to tunable Floquet--spin--orbit band geometry.

cond-mat.mes-hall↗

arXiv2026

Quench dynamics in nonreciprocal Aubry-André-Harper model

The critical phase of a non-Hermitian quasicrystal can support stronger transport than its surrounding delocalized phase. We demonstrate this anomalous behavior in the one-dimensional nonreciprocal Aubry-André-Harper model through a combined study of dynamical quantum phase transitions (DQPTs) and wavepacket diffusion. Using a parity-sorted energy-spectrum classification that directly encodes the generalized $\mathcal{PT}$ symmetry, we find that DQPTs in this system are energy-resolved, in contrast to the energy-independent DQPTs of Hermitian quasicrystals. The energy-resolved features are most pronounced when the initial and final Hamiltonians belong to different phases (localized or extended), and they are tied to the even-odd index structure of the spectrum, which we exploit to organize the quench-dynamical landscape. For wavepacket dynamics after a single-site quench, the diffusion exponent $β$, extracted from the long-time power-law scaling of the root-mean-square displacement $σ(τ)$, partitions the phase diagram into four distinct regimes. In the Hermitian limit the extended phase is ballistic ($β=1$), the critical phase is normally diffusive ($β=0.5$), and the localized phase yields $β\to 0$. Nonreciprocity reverses this hierarchy: the extended phase becomes normally diffusive, while the critical phase turns ballistic. We trace the anomalous $β=1$ at criticality to the self-similar multifractal structure of the critical eigenstates, whose nodal positions are organized by the golden ratio. A finite-size scaling ansatz built on the wave-front propagation yields $σ(τ)\proptoτ$. The parity-resolved DQPTs and the $β$-phase diagram establish two complementary dynamical diagnostics of nonreciprocal quasicrystals, in which nonreciprocity promotes transport at the critical point and suppresses it in the delocalized phase.

cond-mat.mes-hall↗

arXiv2026

Nonreciprocal Control of the Goos--Hänchen Shift via the Barnett Effect in Cavity Magnomechanics

We propose a theoretical scheme for realizing a tunable nonreciprocal Goos-Hänchen shift (GHS) in a hybrid cavity magnomechanical system. The setup consists of a rotating yttrium iron garnet sphere embedded in a microwave cavity, with magnetic-dipole and magnetostrictive interactions mediating magnon-photon and magnon-phonon couplings, respectively. Owing to the Barnett effect, the magnon frequency acquires a rotation-induced shift whose sign can be reversed by changing the direction of the bias magnetic field. We show that the output probe spectrum exhibits a Fano resonance, while the associated GHS responds asymmetrically to opposite field directions, providing a controllable mechanism for nonreciprocal beam shifts. The magnon-photon and magnon-phonon interactions are found to affect the GHS in opposite ways, while the cavity length offers an additional degree of tunability. These results provide a route toward magnetically reconfigurable microwave photonic devices and sensitive detection of Barnett-induced effective fields.

cond-mat.other↗

arXiv2026

Universal quantum corrections of two-body correlation in a weakly interspecies interacting binary Bose mixture

We investigate universal quantum corrections to two-body correlations in a zero-temperature binary Bose mixture using the Cornwall-Jackiw-Tomboulis two-particle-irreducible effective action formalism. In the weak interspecies-coupling regime, a saddle-point treatment based on Hubbard-Stratonovich transformations can be combined with a two-loop expansion and a gapless Hartree-Fock correction, thereby preserving the Goldstone theorem and reducing the coupled two-component problem to two analytically solvable single-component theories. Within this framework, we derive the ground-state energy density as a low-density expansion in the gas parameter, together with the quantum depletion and chemical potentials. The results exhibit a simple mapping to the single-component case: the universal quantum corrections of the mixture are obtained by evaluating the known single-component series at an effective scattering length $a_{σσ}-a_{12}$ for each species, where $a_{σσ}$ and $a_{12}$ are the intra- and interspecies $s$-wave scattering lengths. This reproduces Petrov's equation of state at one-loop order in the weak-coupling limit and yields beyond-Lee-Huang-Yang corrections at two-loop order. We also analyze the role of mass imbalance, which enters the energy density through the exact rescaling factor $(1+m_{1}/m_{2})/2$.

cond-mat.quant-gas↗

arXiv2026

Finite-size reliability of homothetic quantum Otto engines

Homothetic quantum Otto engines---where all populated energy gaps are rescaled by a common factor---provide a reference model in which the quasistatic stochastic efficiency is trajectory-independent while work remains fluctuating. For arbitrary finite homothetic spectra we derive the two-point-measurement work distribution and reduce the first two work moments to endpoint energy moments. Specializing to a uniformly spaced ladder gives closed finite-$N$ expressions for the full work distribution, mean work, variance, and signal-to-width reliability. This ladder connects the qubit and oscillator limits, reveals a finite-$N$ reliability crossover, and demonstrates that the high-temperature and infinite-dimensional limits do not commute. The noncommutation reflects a bounded-versus-unbounded spectral distinction: at fixed finite $N$ the Gibbs state has a normalizable infinite-temperature limit, whereas the oscillator retains an ever-expanding thermal tail. The exact formulas are used to compare standard mean-output prescriptions with work reliability, showing that maximum mean output and maximum dimensionless reliability select different operating points. The benchmark is extended to incomplete diagonal reset and to finite-time unitary strokes described by transition matrices, with a finite-ladder protocol and a harmonic sudden-switch oscillator benchmark as controlled examples. Weak deviations from exact homothety are treated perturbatively, showing how level-dependent gap distortions reintroduce quasistatic efficiency fluctuations and modify work reliability. Together, these results separate finite-size, incomplete thermalization, finite-time, and weak spectral-distortion contributions to work unreliability in quantum Otto engines.

quant-ph↗

arXiv2026

Distinct reentrant transitions in a quasi-periodic Raman lattice

We investigate a one-dimensional lattice with spin-orbit coupling (SOC) and a Zeeman potential containing uniform and quasiperiodic components. By tuning SOC, anomalous mobility edges emerge that separate critical from non-critical states, yielding a reentrant transition between two mixed phases, M$_1$$\to$M$_2$$\to$M$_1$, where M$_1$ (M$_2$) lacks (hosts) anomalous mobility edges. A new \emph{reentrant criticality transition}, defined as multiple entries into the critical phase, is identified. As a counterpart to reentrant delocalization/localization transitions, it completes the basic framework of reentrant phenomena across extended, localized, and critical states. The uniform Zeeman potential drives a reentrant delocalization transition, arising from the splitting of the localized region induced by the shift of mobility edges. This reveals a distinct pathway for reentrant phenomena beyond hybridization mechanisms.

cond-mat.dis-nn↗

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

Lyapunov Exponents as Duality-Invariant Signatures of Critical States

Critical eigenstates are usually identified through wave-function geometry in a chosen basis, such as participation ratios, multifractal spectra, or finite-size scaling. Here we formulate criticality instead as a dual-space Lyapunov property. We prove a Fourier exclusion principle: exponential localization in one representation is incompatible with exponential localization in its Fourier-dual representation. This turns the Liu--Xia condition, $γ_x(E)=γ_m(E)=0$, from a phenomenological criterion into a rigorous length-scale statement: a critical state is characterized by the simultaneous absence of exponential confinement in real and momentum space. The criterion is invariant under bounded local gauge transformations of the transfer matrix and remains compatible with conventional single-space multifractal diagnostics. More importantly, it is exactly predictive. In analytically tractable quasiperiodic models, the same condition yields closed-form critical lines, an exact finite critical region with an additional critical branch, and a complex critical surface in a non-Hermitian non-self-dual spectrum. Thus the Liu--Xia condition provides not only a diagnostic of critical states, but an exact solvability principle for locating critical sets across distinct microscopic structures.

cond-mat.dis-nn↗

arXiv2026

Coherence-Preserving Fluctuation Diagnostics for an Engineered Population-Inverted Qubit Otto Engine

Finite-time quantum thermal machines require diagnostics beyond average work and efficiency, because microscopic engines operate in regimes where fluctuations, incomplete thermalization, and coherence are equally important. Here we develop a measurement-backaction-free (coherence-preserving) fluctuation diagnostic for an engineered qubit Otto engine coupled to an actively maintained population-inverted hot channel. The engine is analyzed using a dynamic Bayesian network (DBN) reconstruction of the unmeasured coherent cycle, yielding work, heat, power, and normalized efficiency-proxy fluctuations without imposing the projective dephasing inherent in two-point energy measurements. The inverted channel is treated as an active reduced-model resource; accordingly, all reported power and efficiency enhancements represent gross working-medium advantages, not net device efficiencies. In the full-thermalization limit, population inversion enhances extracted work and output power while opening a stability sector with markedly reduced relative power fluctuations. When finite-duration isochores are implemented, this gross enhancement reorganizes into a structured operating landscape with distinct high-power, high-efficiency, and low-relative-noise sectors, whose boundaries are governed by the competing timescales of nonadiabatic driving and thermalization rates. A direct comparison reveals that DBN and conventional two-point measurement predictions diverge precisely in coherence-rich regimes, identifying where a backaction-free reconstruction is essential. A coherence-sensitive analysis further shows that the positive-temperature reference operates optimally in an almost decohered region, whereas the inverted high-efficiency branch remains aligned with the dominant post-hot-bath coherence ridge. These results provide a reduced-model benchmarking framework for engineered qubit thermal machines.

quant-ph↗

arXiv2026

Unbound States and Mixed Bound--Unbound Phases in Near-Infinitely Deep Potentials

We investigate the robustness of unbound states in one-dimensional quasiperiodic models with near-infinitely deep potentials. By constructing a deeper extension of the Liu-Xia model and combining inverse participation ratio (IPR) calculations with Lyapunov-exponent analysis based on Avila's global theory, we show that increasing the potential depth does not eliminate unbound states. Instead, it shifts and narrows their energy window to $-2t-V<E<2t-V$. We further extend the analysis to non-Hermitian quasiperiodic potentials with gain and loss. In these systems, unbound states survive within analytically determined real-energy intervals, but they no longer occupy the whole interval uniformly; rather, they coexist with bound states and form a mixed bound-unbound phase. The corresponding boundaries between the mixed region and the pure bound-state regions are obtained exactly from the Lyapunov exponent. These results demonstrate that unbound states in extreme quasiperiodic potentials are controlled not only by the potential depth but also by the spectral and localization structures induced by non-Hermiticity.

cond-mat.dis-nn↗

arXiv2026

Goos-Hänchen Shift in $\mathcal{PT}$-Symmetric and Passive Cavity Optomechanical Systems

We theoretically investigate the control of the Goos-Hänchen shift (GHS) of a reflected weak probe field in both parity-time ($\mathcal{PT}$)-symmetric and conventional optomechanical systems. The proposed scheme consists of a single optomechanical platform where a passive optical cavity is coupled to an active mechanical resonator, in contrast to standard passive-passive configurations. Analysis of the eigenfrequency spectrum reveals the emergence of an exceptional point under balanced gain-loss conditions at a tunable effective optomechanical coupling strength. Using the transfer-matrix method combined with stationary-phase analysis, we examine the GHS across broken and unbroken $\mathcal{PT}$ phases and compare it with that in the conventional system. The lateral shift exhibits strong phase dependence: it is markedly enhanced in the unbroken regime relative to both the broken phase and the passive configuration. We further show that the GHS can be actively tuned through the cavity detuning and the intracavity medium length. These results provide a controlled means for manipulating beam shifts in optomechanical systems and suggest pathways toward tunable photonic components and precision optical sensing.

physics.optics↗

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↗

arXiv2026

Spectroscopic readout of chiral photonic topology in a single-cavity spin-orbit-coupled Bose-Einstein condensate

Topological photonic phases are typically identified through band reconstruction, steady-state transmission, or real-space imaging of edge modes. In this work, we present a framework for spectroscopic readout of chiral photonic topology in a single driven optical cavity containing a spin-orbit-coupled Bose-Einstein condensate. We demonstrate that the cavity transmission power spectral density provides a direct and measurable proxy for a momentum- and frequency-resolved photonic Chern marker, enabling topological characteristics to be inferred from spectral data without the need for bulk-band tomography. In the loss-dominated regime, where cavity decay exceeds atomic dissipation, the power spectral density exhibits Dirac-like gapped hybrid modes with a vanishing Chern marker, indicating a trivial phase. When the dissipation imbalance is reversed, a bright, gap-spanning spectral ridge emerges, co-localized with peaks in both the Chern marker and Berry curvature. The complex spectrum reveals parity-time symmetric coalescences and gain-loss bifurcations, marking exceptional points and enabling chiral, gap-traversing transport. By linking noise spectroscopy to geometric and non-Hermitian topology in a minimal cavity-QED architecture, this work provides a framework for spectroscopic detection of topological order in driven quantum systems. This approach offers a pathway to compact, tunable topological photonics across a broad range of light-matter platforms, providing a method for the study and control of topological phases in hybrid quantum systems.

quant-ph↗

arXiv2026

Thermodynamic modes of a quasiperiodic mobility-edge system in a quantum Otto cycle

We investigate thermodynamic operation of a quasiperiodic lattice with an exact mobility edge, described by the Biddle--Das Sarma model. We use this model as the working medium of a quantum Otto cycle and map its operating mode as a function of the hopping-range parameter $p$, the initial and final potential strengths $V_i$ and $V_f$, and two idealized protocols for the isolated strokes. In a near-adiabatic (state-frozen) protocol, where the density matrix is approximately unchanged during the isolated strokes, the cycle supports only two modes: a \emph{heater} and an \emph{accelerator}. In an adiabatic protocol, where level populations are preserved while the spectrum is deformed, two additional modes appear: a \emph{heat engine} and a \emph{refrigerator}. Our results show that mobility-edge systems can realize multiple thermodynamic functions within a single platform and provide guidance for switching between modes by tuning $p$, $V_i$, and $V_f$.

cond-mat.dis-nn↗

arXiv2026

Quantum Mpemba effect in quasiperiodic systems

We study a one-dimensional quasiperiodic tight-binding model with simultaneous off-diagonal (hopping) and diagonal (onsite) modulations. Using the inverse participation ratio and the wave-packet centroid, we construct localization-delocalization phase diagrams for both equilibrium and nonequilibrium steady states. We analyze the robustness of initial-state properties under dissipation and characterize dissipation-induced localization-delocalization transitions (and their reversals) in detail. Trace-distance dynamics provide evidence for a quantum Mpemba effect: states prepared farther from the steady state can relax faster than states initialized closer to it. We propose a starting-line hypothesis that explains the presence or absence of this effect across parameter regimes. These results advance the understanding of steady-state phase transitions and relaxation dynamics in dissipatively driven quasiperiodic systems.

cond-mat.dis-nn↗

arXiv2026

Wigner distribution, Wigner entropy and Quantum Refrigerator of a One-Dimensional Off-diagonal Quasicrystal

We investigate an off-diagonal quasicrystal featuring simultaneous off-diagonal and diagonal quasiperiodic modulations. By analyzing the fractal dimension, we map out the delocalization-localization phase diagram. We demonstrate that delocalized and localized states can be distinguished via the Wigner distribution, while extended, critical, and localized phases are separated using the Wigner entropy. Furthermore, we explore the quantum thermodynamic properties, revealing that localized states facilitate the emergence of a quantum heater mode, alongside the appearance of a refrigerator mode. These findings enhance our understanding of localization phenomena and expand the thermodynamic applications of quasiperiodic systems.

cond-mat.stat-mech↗

arXiv2026

Coherent Control of the Goos-Hänchen Shift in Polariton Optomechanics

We propose a theoretical scheme for controlling the Goos-Hänchen shift (GHS) of a reflected probe field in a polariton optomechanical system. The system comprises an optical mode, a molecular vibrational mode, and $N$ excitonic modes, where excitons couple to molecular vibrations via conditional displacement interactions and to photons through electric dipole interactions. We show that the effective exciton-vibration coupling provides a powerful mechanism for coherent GHS control: in its absence, the system exhibits a pronounced GHS at resonance, while activating it strongly suppresses the shift. The effective cavity detuning and the cavity length serve as additional tunable parameters for GHS manipulation. Furthermore, increasing the collective exciton-optical coupling enhances the GHS. Our results establish a framework for probing the GHS in polariton optomechanical systems and offer new avenues for designing optical devices that exploit beam-displacement phenomena.

physics.optics↗