arXiv subjects

Zhen-Gang Zhu

Publications and source records attributed to Zhen-Gang Zhu.

At least 19 recordsLinked to original sources

arXiv2026

Anomalous Thomson Effect

We formulate an effect called the anomalous Thomson effect (ATE), which constitutes the Thom?son counterpart to the anomalous Hall effect and anomalous Nernst effect (ANE). The anomalous Thomson coefficient (ATC) is determined by the anomalous Nernst coefficient (ANC) together with the temperature dependence of both the ANC and the longitudinal electrical conductivity; This relation is model independent within local linear response and holds for the total anomalous Nernst coefficient, irrespective of whether its microscopic origin is intrinsic or extrinsic. Specifically, we study a massive Dirac model for Fe3Sn2 to capture intrinsic Berry-curvature-driven transport, where the Berry curvature near the gapped Dirac cones enhances the ANC-related contributions to the ATC, and we also deduce the ATC from measured experimental data reported for CoS2,Co3Sn2S2, and CeCrGe3. In the low-temperature limit, the ratio ATC/ANC approaches three, and we find that the ATC for CeCrGe3 can be as large as ten times the ANC in the liquid-nitrogen temperature regime, making this effect highly attractive for solid-state thermoelectric refrigeration in this temperature range. It is important to emphasize that the formulated ATE can be directly verified using existing ANE and longitudinal conductivity data, without the need for additional equipment or measurements.

cond-mat.mes-hall↗

arXiv2026

Anomalous Hall and Nernst effects driven by static and fluctuating spin chiralities on Kagome lattice

We theoretically investigate the anomalous Hall and Nernst effects (AHE and ANE) in a two dimensional Kagome lattice to uncover the distinct roles of static and fluctuating scalar spin chi ralities. Employing Monte Carlo simulations incorporating with a tight binding Hamiltonian via the s-d exchange interaction, we explicitly evaluate the anomalous transport coefficients. A key finding is the systematic disentanglement of the macroscopic responses into an intrinsic contribu tion, governed by momentum space Berry curvature induced by static chirality, and an extrinsic skew scattering contribution driven by real space dynamical spin fluctuations. We demonstrate a pronounced mechanistic crossover: deep in magnetically ordered phases like the skyrmion crystal, the intrinsic Berry curvature dictates the transport behavior. However, approaching the magnetic order-disorder critical regime, strong thermal fluctuations disrupt static noncoplanar spin configu rations, drastically suppressing intrinsic responses. Here, dynamical chiral fluctuations emerge as the dominant driving force. By delineating the phase regimes governed by static versus fluctuating chiralities, this work elucidates the distinct microscopic mechanisms dictating anomalous transport in frustrated magnetic systems.

cond-mat.str-el↗

arXiv2026

Fundamental Relations as the Leading Order in Nonlinear Thermoelectric Responses with Time-Reversal Symmetry

In recent years, nonlinear transport phenomena have garnered significant interest in both theoretical explorations and experiments. In this work, we utilize the semi-classical wave packet theory to calculate disorder-induced second-order transport coefficients: second-order electrical ($σ$), thermoelectric ($α$), and thermal ($κ$) coefficients, capturing the interplay between side-jump and skew-scattering contributions in systems with time-reversal symmetry. Using a topological insulator model, we quantitatively characterize the Fermi-level dependence of these second-order transport coefficients by explicitly including Coulomb impurity potentials. Furthermore, we elucidate the relationships between these coefficients, establishing the second-order Mott relation and the Wiedemann-Franz law induced by disorder. This study develops a comprehensive theoretical framework elucidating the nonlinear thermoelectric transport mechanisms in quantum material systems.

cond-mat.mes-hall↗

arXiv2026

Correlated $\mathcal{PT}$-Symmetric Antiferromagnetic Topological Insulators with Giant Nonlinear Anomalous Thermoelectrics

Topological states in antiferromagnets (AFMs) offer a promising platform for exploring novel physical phenomena and advancing the applications of AFM spintronics. The AFM topological insulator (TI) state stands out as one of the most representative and prominent cases. Unlike the previously proposed AFM-TI states in noninteracting systems, here we employ an extended Kane-Mele-Hubbard model to demonstrate that electron correlations can give rise to a $\mathcal{PT}$-symmetric AFM-TI state. This state breaks both spatial inversion symmetry $\mathcal{P}$ and time-reversal symmetry $\mathcal{T}$, and enables intrinsic topological nonlinear responses to dominate the leading-order dynamics of the system. The competition between electron correlations and spin-orbit coupling drives the system across a topological phase transition, where the closure of the bulk band gap induces singular behaviors in higher-order quantum geometric tensors. Such microscopic singular characteristics manifest macroscopically as pronounced enhancements in thermoelectric performance, charge conductivity, and thermal conductivity. These giant tunable transport signatures, which can be effectively modulated by mechanical strain and electrostatic gating, provide a feasible experimental route to probe and understand correlated topological materials.

cond-mat.mes-hall↗

arXiv2026

Intrinsic violation of the Wiedemann-Franz law in interacting systems

The Wiedemann-Franz (WF) law dictates a universal ratio between thermal and electrical conductivities, is widely obeyed by Fermi liquid systems. Here, we identify a fundamental yet often overlooked, thermodynamic mechanism for the violation of WF law: the temperature-dependent renormalization of the electronic band structure. We demonstrate that the interaction-induced energy drift $\partialε_k/\partial T$, acts as an effective driving force that fundamentally decouples heat transport from charge transport. We derive a generalized transport relation linking the Lorenz ratio deviation directly to the thermoelectric response. Our findings provide a unified framework for understanding thermal transport in interacting topological phases and suggest the Lorenz ratio as a probe for distinguishing topological robustness from Fermi liquid instabilities.

cond-mat.mes-hall↗

arXiv2026

Odd-even parity dependent transport in an annular Kitaev chain

We investigate the impact of magnetic flux and the odd-even parity of lattice points $N$ on electron transport in an annular Kitaev chain, with an explanation provided from the energy band perspective. Three transport mechanisms including direct transmission (DT), local Andreev reflection (LAR) and crossed Andreev reflection (CAR) are considered. In particular, the connection configuration of electrodes to different lattice sites is studied, where the case that the two electrodes connected to the sites are aligned along a diameter is called as symmetric connection and otherwise as asymmetric connections. For even $N$ and asymmetric connection, the vanished LAR and CAR in symmetric connection will emerge as peaks. A more prominent observation is that the symmetry of the two resonant peaks due to DT processes located at $Φ= Nπ/3$ and $Φ= 2Nπ/3$ for symmetric connection will be broken, and the peak at $Φ= Nπ/3$ will be largely reduced, where $Φ$ is the magnetic flux. Moreover, the peaks around $Φ= Nπ/3$ due to LAR and CAR processes grows drastically even larger than that from DT. For LAR and CAR processes, there is no peak around $Φ= 2Nπ/3$ and transmission due to these two processes are completely suppressed for $Φ>Nπ/2$. Moreover, it is found that the energy bands vary with $Φ$ in a period of $Nπ$ and $2Nπ$ for even or odd $N$. We finally systematically analyze the influence of weak disorder on transport and demonstrate that these parity-dependent effects are robust in the presence of disorder. These behaviors reflect a complicated competition from DT, LAR and CAR processes and the parity of the lattice number in the Kitaev ring, which will be interested for the quantum device based on Kitaev chain.

cond-mat.supr-con↗

arXiv2025

Electro-optic Kerr Effect Induced by Nonlinear Transport in monolayer WTe2

The nonlinear Hall effect (NLHE) can induce optical anisotropy by modifying a material's dielectric tensor, presenting opportunities for novel characterization and device applications. While the magneto-optical Kerr effect (MOKE) probes the linear Hall effect (LHE) in magnetic materials, an analogous optical probe for NLHE in non-magnetic, time-reversal symmetric systems remains highly desirable. Here, we theoretically propose and investigate an NLHE-induced Electro-optic Kerr Effect (EOKE) as such a probe. Focusing on monolayer (ML) WTe$_2$, a prototypical NLHE material, our analysis considers contributions from Berry curvature dipole (BCD), Drude, injection, and shift mechanisms. We demonstrate that the EOKE signal in WTe$_2$ is predominantly governed by the BCD. Furthermore, the Kerr angle exhibits temporal oscillations at different optical frequencies, suggesting EOKE as a promising route for the time-resolved detection of NLHE and the dynamic investigation of material topology.

cond-mat.other↗

arXiv2025

The second-order intrinsic Wiedemann-Franz law

In recent years, the nonlinear anomalous thermal Hall effect has attracted substantial attention. In this paper, we carry out a theoretical exploration of the intrinsic anomalous thermal Hall and Nernst effect that is induced by the thermal Berry connection polarizability. This effect is independent of the relaxation time and can be present in antiferromagnets possessing PT symmetry. Additionally, we put forward a second-order intrinsic Wiedemann-Franz law, which represents the ratio of the second-order intrinsic thermal conductivity coefficient to the second-order intrinsic electrical conductivity coefficient . When analyzed within a four-band PT symmetric Dirac model, we observe that the second-order intrinsic thermal conductivity coefficient is linearly proportional to the second-order intrinsic electrical conductivity coefficient , and the second-order intrinsic Wiedemann-Franz law is characterized by the chemical potential $μ$ in the low-temperature regime. These findings provide significant implications for experimental verification.

cond-mat.mes-hall↗

arXiv2024

Magnon Landau-Zener tunnelling and spin current generation by electric field

To control the magnon transport in magnetic systems is of great interest in magnonics. Due to the feasibility of electric field, how to generate and manipulate magnon with pure electrical method is one of the most desired goals. Here we propose that the magnon spin current is generated by applying time-dependent electric field, where the coupling between the magnon and electric field is invoked via Aharonov-Casher effect. In particular, the magnon spin current is dominated by electric field component which perpendicular to the magnetization direction. We apply our theory to 1D ferromagnetic SSH model and show that the generated magnon spin current is closely related to the band geometry. Our findings expands the horizons of magnonics and electric-control-magnon mechanisms.

cond-mat.mes-hall↗

arXiv2024

Effect of disorder on Berry curvature and quantum metric in two-band gapped graphene

The geometric properties of parameter space are mostly described by Berry curvature and quantum metric, which are the imaginary and real part of quantum geometric tensor, respectively. In this work, we calculate the dressed Berry curvature and quantum metric containing eight Feynman diagrams, which are proportional to the leading-order of the concentration of impurities. For a two-band gapped graphene model, we find the disorder does not break the original symmetry but decrease (increase) the absolute value of Berry curvature and quantum metric in conduction (valence) band. We show how impurities affect the Berry curvature and quantum metric, deepening our understanding of the impurity effect on the electron transport properties in two-band gapped graphene.

cond-mat.mes-hall↗

arXiv2024

Intrinsic Second Order Spin Current

In recent years, nonlinear Hall effect has attracted great attention with three different terms contributed by Drude effect, Berry curvature dipole and Berry connection polarizability. In this work, we theoretically predict an intrinsic second order spin current induced by spin-dependent Berry curvature polarizability based on time-independent perturbation theory. We show other two second order spin conductivities contributed by the group velocity and spin-dependent Berry curvature dipole.A two-dimensional Rashba-Dresselhaus spin-orbit coupled system is studied as an example, and it is found that the intrinsic second order contribution plays a major role in the region of $μ>0$, while current mainly comes from the extrinsic terms when $μ<0$. Thus, the dependence of spin conductivity on chemical potential is expected to distinguish the extrinsic and intrinsic contributions experimentally.

cond-mat.mes-hall↗

arXiv2024

Magnon spin photogalvanic effect induced by Aharonov-Casher phase

Magnons are electrically neutral bosonic quasiparticles emerging as collective spin excitations of magnetically ordered materials, and play a central role in the next-generation spintronics owing to its obviating Joule heating. A difficult obstacle for quantum magnonics is that the magnons do not couple to the external electric field directly so that a direct electric manipulation via bias or gate voltage as in conventional charge-based devices seems not applicable. In this work, we propose a new mechanism in which magnons can be excited and controlled by electric field of light directly. Since the electric field of light can be tuned in a wide and easy way, the proposal is of great interest in realistic applications. We call it as the magnon spin photogalvanic effect (SPGE), which comes from five contributions: the Drude, Berry curvature dipole (BCD), injection, shift, and rectification, with distinct geometric origins. We further show that the responses to linearly-polarized or circularly-polarized light are determined by band-resolved quantum metric or Berry curvature, the two combined together just comprise of a quantum geometric tensor. The proposed magnon SPGE can be measured by a characterized topological phase transition. We also discuss a breathing kagome-lattice model of ferromagnets and suggest possible candidate materials to implement it.

cond-mat.mes-hall↗

arXiv2024

Intrinsic Second-Order magnon Thermal Hall Effect

In this paper, we study the intrinsic contribution of nonlinear magnon thermal Hall Effect. We derive the intrinsic second order thermal Hall conductivity of magnon by the thermal scalar potential (TSP) method and the thermal vector potential (TVP) method. We find that the intrinsic second order magnon thermal Hall conductivity is related to the thermal Berry-connection polarizability (TBCP). We apply our theory to the monolayer ferromagnetic Hexagonal lattice, and we find that the second order magnon thermal Hall conductivity can be controlled by changing Dzyaloshinskii-Moriya strength and applying strain.

cond-mat.mes-hall↗

arXiv2023

Van Hove singularity-induced negative magnetoresistance in Dirac semimetals

Negative magnetoresistance (NMR) is a marked feature of Dirac semimetals, and may be caused by multiple mechanisms, such as the chiral anomaly, the Zeeman energy, the quantum interference effect, and the orbital moment. Recently, an experiment on Dirac semimetal Cd$_3$As$_2$ thin films revealed a new NMR feature that depends strongly on the thickness of the sample [T. Schumann, \emph{et al}., Phys. Rev. B 95, 241113(R) (2017)]. Here, we introduce a new mechanism of inducing NMR via the presence of the van Hove singularity (VHS) in the density of states. Theoretical fitting of the experimental data on magnetoconductivity and magnetoresistance shows good agreement, indicating that the observed NMR in thin films of Cd$_3$As$_2$ can be attributed to the VHS. This work provides new insights into the underlying of Dirac semimetals.

cond-mat.mes-hall↗

arXiv2023

An intrinsic nonlinear Ohmic current

It is known that intrinsic currents in magnetic metals often appear in the direction perpendicular to the external field for linear and nonlinear responses. Distinct from three kinds of known nonlinear currents, namely, the Drude contribution, the Berry curvature dipole induced current and the Berry connection polarization induced current, here we report a intrinsic nonlinear current with breaking time-reversal symmetry. This new kind of intrinsic nonlinear current from the nontrivial Berry connection polarizability may emerge in the longitudinal or transverse direction, and both are dissipative Ohmic currents. We unveil 66 magnetic point group symmetries that can accommodate such nonlinear current, and possible candidate materials are proposed. This theory is also applied to observe the nonlinear current we proposed in one- and two-dimensional Dirac systems as examples.

cond-mat.mes-hall↗

arXiv2023

Photogalvanic effect and second harmonic generation from radio to infrared region in WTe$_2$ monolayer

Second-order nonlinear optical responses, including photogalvanic effect (PGE) and second harmonic generation (SHG), are important physical phenomena in nonlinear optics. The PGE (SHG) related to linearly and circularly polarized light are called the linear and circular PGE (LPGE and CPGE) [linear and circular SHG (LSHG and CSHG)], respectively. In this work, we use the quantum kinetics under relaxation time approximation to study the dependence of second-order nonlinear optical responses on Fermi level and frequency under different out-of-plane electric fields in WTe$_2$ monolayer from radio to infrared region. We find that the maximum frequency at which the Berry curvature dipole mechanism for the nonlinear Hall effect plays a major role is about 1 THz. In radio and microwave regions, two large peaks of nonlinear conductivities occur when the Fermi level is equal to the energy corresponding to gap-opening points. In terms of frequency, in radio region, LPGE and SHG conductivities maintain a large constant while the CPGE conductivity disappears. In microwave region, LPGE and SHG start to decrease with increasing frequency while the CPGE is large. In 125-300 THz region and in y direction, the presence of DC current without the disturbance of second harmonic current under circularly polarized light may be useful for fabricating new optoelectronic devices. Moreover, we illustrate that when calculating the nonlinear optical responses of practical materials, the theories in the clean limit fail and it is necessary to use a theory that considers scattering effects. We also point out that for materials with femtosecond-scale relaxation times and complex energy band structures, the quantum kinetics is more accurate than the semi-classical Boltzmann equation method. Besides, phenomenological expressions of PGE and SHG are provided.

cond-mat.mes-hall↗

arXiv2023

Field-induced Berry connection and planar Hall effect in tilted Weyl semimetals

We propose the linear and nonlinear planar Hall effect (PHE) in tilted Weyl semimetals in the presence of an in-plane magnetic and electric field, where the field-induced Berry connection (FBC) plays a key role. We show that the PHE is ascribed to the quantum metric, distinct from the well-known chiral anomaly-induced PHE arising from the Berry curvature. Using a tilting vector to describe the model, we demonstrate the constrains on the linear and nonlinear PHE by the tilting directions. The linear PHE is intrinsic that is determined by the topological properties of energy bands, whereas the nonlinear PHE is extrinsic. The predicted linear and nonlinear PHE are inherently different from others and may shed light on a deeper understanding on transport nature of the tilted Weyl semimetals.

cond-mat.mes-hall↗

arXiv2022

Spatial spin-spin correlations of the single-impurity Anderson model with a ferromagnetic bath

We investigate the interplay between the Kondo effect and the ferromagnetism by an one dimension Anderson impurity model with a spin partially polarized bath, using the projective truncation approximation under Lacroix basis.The equal-time spatial spin-spin correlation function (SSCF) is calculated. For the case of spin-unpolarized conduction electrons, it agrees qualitatively with the results from density matrix renormalization group (DMRG). For system with partially spin-polarized conduction electrons, an oscillation in the envelope of SSCF emerges due to the beating of two Friedel oscillations associated to two spin-split Fermi surfaces of conduction electrons. The period is proportional to the inverse of magnetic field $h$. A fitting formula is proposed to perfectly fits the numerical results of SSCF in both the short- and long-range regions. For large enough bath spin polarization, a bump appears in the curve of the integrated SSCF. It marks the boundary between the suppressed Kondo cloud and the polarized bath sites.

cond-mat.str-el↗