arXiv subjects

Xiao-Qin Yu

Publications and source records attributed to Xiao-Qin Yu.

12 recordsLinked to original sources

arXiv2026

Electric-field controlled nonlinear anomalous Nernst effect in two-dimensional time-reversal symmetric systems

It's established that the nonlinear anomalous Nernst effect (NANE), originating from Berry curvature near the Fermi energy, is symmetry-permitted only when a single mirror symmetry exists in the transport plane of two-dimensional (2D) materials. Here, we show that an applied direct electric field can lift this symmetry constraint, enabling an electric-field-induced NANE emerge in time-reversal symmetric 2D systems with higher crystallographic symmetries. This electric-field-induced NANE arises from both Berry connection polarization, rooted in the electric-field-corrected Berry curvature, and the anomalous-velocity-modified nonequilibrium Fermi distribution function. Additionally, we propose an alternating temperature gradient as a driving force instead of the conventional steady one, ensuring experimental detection of NANE via second-harmonic measurement techniques. The behaviour of electric-field-induced NANE in the monolayer graphene has been theoretically and systematically investigated.

cond-mat.mes-hall↗

arXiv2025

Intrinsic nonlinear valley Nernst effect in the strained bilayer graphene

We theoretically analyze the nonlinear valley Nernst effect (NVNE) as the second-order response of temperature gradient through the semiclassical framework of electron dynamics. Our study shows that an intrinsic nonlinear pure valley current can be generated vertically to the applied temperature in the materials with both inversion and time-reversal symmetries. This intrinsic NVNE has a quantum origin from the quantum metric and shows independence from the relaxation time. We find that the local largest symmetry near the valleys for the nonvanishing intrinsic NVNE is a single mirror symmetry in two-dimensional systems. We theoretically investigate the intrinsic NVNE in the uniaxially strained gapless bilayer graphene and find the intrinsic NVNE can emerge when applying the temperature gradient vertically to the direction of strain. Interestingly, a transition from the compressive strain to the tensile one results in the sign reversal of the intrinsic NVNE.

cond-mat.mes-hall↗

arXiv2025

The unidirectional Seebeck detection of the N\'{e}el vector in the two-dimensional tetragonal $\mathcal{PT}$-symmetric antiferromagnetic materials

The efficient detection of the reversal (180$^{\circ}$ rotation) of the N\'{e}el vector is one of the crucial tasks in antiferromagnetic spintronics. Here, we propose a thermal approach to detect the reversal of the N\'{e}el vector in the tetragonal $\mathcal{PT}$ antiferromagnetic materials through the unidirectional Seebeck effect (USE). Being different from the previous works in which USE stems from the global Rashba spin-orbit coupling (SOC) or asymmetric magnon scattering, we find that the USE originates from the coupling of the hidden Rashba SOC and the N\'{e}el vector in the tetragonal $\mathcal{PT}$ antiferromagnetic materials in the absence of the global Rashba SOC. Using a generic minimal model, we analyse the behaviors of the USE for the two-dimensional tetragonal lattice $\mathcal{PT}$ antiferromagnet. Importantly, It's found that when the N\'{e}el vector is reversed, the sign of the USE changes, which can be utilized to detect the reversal of the N\'{e}el vector.

cond-mat.mes-hall↗

arXiv2025

Extrinsic nonlinear acoustic valley Hall effect in the massive Dirac materials

The nonlinear acoustic valley Hall effect (AVHE), a recently discovered novel acoustically driven phenomena, has sparked extensive interests in valleytronics. So far, only the intrinsic contributions from band structure (Berry curvature or asymmetric energy dispersions) to nonlinear AVHE have been investigated. Here, we theoretically investigate the nonlinear AVHE from both intrinsic and extrinsic contributions in two-dimensional (2D) hexagonal massive Dirac materials with disorders based on the Boltzmann formalism and also concretely analyse the behaviours of nonlinear AVHE in disordered monolayer MoS2. It's found that the extrinsic contributions (side jump and skew scattering) can also give rise to a pure nonlinear AVHE in the 2D hexagonal massive Dirac materials. Remarkably, the extrinsic mechanisms dominate the nonlinear AVHE in the disordered monolayer MoS2.

cond-mat.mes-hall↗

arXiv2024

Strongly enhanced nonlinear acoustic valley Hall effect in tilted Dirac materials

It has been recently established that a nonlinear valley current could be generated through traveling a surface acoustic wave (SAW) in two-dimensional Dirac materials. So far, the SAW-driven valley currents have been attributed to warping Fermi surface or Berry phase effect. Here, we demonstrate that tilt mechanism can also lead to a nonlinear valley Hall current (VHC) when propagating SAW in materials with the tilted Dirac cone placed on a piezoelectric substrate. It's found that the nonlinear VHC exhibits a $\sin\theta$ dependence on the orientation of tilt with respect to SAW. In addition, this tilt-induced nonlinear acoustic VHC shows independence on the relaxation time, distinguishing from the contributions from the Berry phase or trigonal warping. Remarkably, the magnitude of the nonlinear acoustic VHC from tilt mechanism in the uniaxially strained graphene is two orders larger than those reported in MoS$_2$ stemmed from the Berry phase effect and the warping effect.

cond-mat.mes-hall↗

arXiv2023

Unidirectional Seebeck effect from Rashba spin-orbit coupling on the subsurface of Ge(111)

A new nonlinear magnetothermal effect, namely unidirectional Seebeck effect(USE), has been recently reported in magnetic/nonmagnetic topological insulator (TI) heterostructure and is ascribed to the asymmetry magnon scattering. Here, we show a new mechanism to generate USE in the Rashba two dimensional electron gas (2DEG), in which the magnetism or magnetic order is completely absent. It's found that the USE has a quantum origin from the spin-momentum locking generated from Rashba spin-orbit coupling. We find that the USE exhibits a sine dependence on the orientation of the magnetic field with respect to the direction of the temperature gradient and is dominant from the states above the Lifshitz point. The USE in the semiconductor Ge(111) subsurface states has been theoretically and systematically investigated.

cond-mat.mes-hall↗

arXiv2022

Band tilt induced nonlinear Nernst effect in topological insulators: An efficient generation of high-performance spin polarization

Topological insulators (TIs) hold promise as a platform for spintronics applications due to the fascinating spin-momentum locking (SML) of the surface states. One particular interest lies in using TIs as spin-polarized sources for spintronics structures. Here, we propose the band tilt induced nonlinear Nernst effect (NLNE) in TIs as a clean and efficient route to generate high-performance spin polarization (SP). We show that in the presence of SML and hexagonal warping effect a finite band tilt can induce an imbalance of two spin carriers and effectively give rise to spin-polarized NLNE current in TIs. In our scheme, both the spin current and charge current regime can be achieved under the thermal drive. The obtainable SP can be efficiently tuned in either a smooth or rapid way, exhibiting highly flexible tunability. In addition, near-unity SP can be generated within a wide range of tunable parameters, which is also found to be robust against temperature. Therefore, our work provides a mechanism to realize controllable room-temperature high-degree SP based on TIs, which is of essential importance for future spintronics applications.

cond-mat.mes-hall↗

arXiv2021

Fundamental Distinction between Intrinsic and Extrinsic Nonlinear Thermal Hall Effects

We theoretically investigated the fundamental distinction between intrinsic and extrinsic nonlinear thermal Hall effect in the presence of disorder at the second-order response to the temperature gradient in terms of the semi-classical Boltzmann equation. We found that, at low temperatures, the intrinsic contribution of the nonlinear thermal Hall conductivity is proportional to the square of temperature, whereas the extrinsic contributions (side-jump and skew-scattering) are independent of temperature. This distinct dependency on temperature provide a new approach to readily distinguish the intrinsic and extrinsic contributions. Specifically, we analysed the nonlinear thermal Hall effect for a tilted two-dimensional massive Dirac material. In particular, we showed that when the Fermi energy is located at the Dirac point, the signal is solely from the intrinsic mechanism; when the Fermi energy is higher, the extrinsic contributions are dominant, which are uncovered to be two to three orders of magnitude larger than the intrinsic contribution.

cond-mat.mtrl-sci↗

arXiv2020

Hexagonal Warping Induced Nonlinear Planar Nernst Effect in Nonmagnetic Topological Insulators

We propose theoretically a new effect, i.e. nonlinear planar Nernst effect (NPNE), in nonmagnetic topological insulator (TI) Bi2Te3 in the presence of an in-plane magnetic field. We find that the Nernst current scales quadratically with temperature gradient but linearly with magnetic field and exhibits a cosine dependence of the orientation of the magnetic field with respect to the direction of the temperature gradient. The NPNE has a quantum origin arising from the conversion of a nonlinear transverse spin current to a charge current due to a joint result of hexagonal warping effect, spin-momentum locking, and the time-reversal symmetry breaking induced by the magnetic field.

cond-mat.mes-hall↗

arXiv2019

Unidirectional Seebeck effect in magnetic topological insulators

We theoretically investigate the temperature gradient-dependent or unidirectional Seebeck effect (USE) in a magnetic/ nonmagnetic topological insulator (TI) heterostructure with in-plane magnetization in terms of the semiclassical electron dynamics and Fermi golden rule. The USE has a quantum origin arising from the magnon asymmetric scattering of surface Dirac electrons on TI. We discuss the USE in the heterostructures, Cr$_{x}$(Bi$_{1-y}$Sb$_y$)$_{2-x}$Te$_{3}$/ (Bi$_{1-y}$Sb$_{y})_2$Te$_{3}$. The USE exhibits $\cosϕ$-dependence (measured from $y$-direction) on the orientation of magnetization. It's found that the sign of USE stays unchanged when the system is transferred from $p$-doping to $n$-doping. The USE shows on inverse-linearly temperature dependent at high temperature.

cond-mat.mes-hall↗

arXiv2019

Topological Nonlinear Anomalous Nersnt Effect in Strained Transition Metal Dichalcogenides

We theoretically analyze the non-linear anomalous Nernst effect as the second-order response of temperature gradient by using the semiclassical framework of electron dynamics. We find that a non-linear current can be generated transverse to the applied temperature gradient in time-reversal-symmetry materials with broken inversion symmetry. This effect has a quantum origin arising from the Berry curvature of states near the Fermi surface. We discuss the non-linear Nernst effect in transition metal dichalcogenides~(TMDCs) under the application of uniaxial strain. In particular, we predict that under fixed chemical potential in TMDCs, the non-linear Nernst current exhibits a transition from $\textbf{j}^\text{dip}_\text{A}\sim T^{-2}$ temperature dependence in low temperature regime to a linear $T$-dependence in high temperature.

cond-mat.mes-hall↗

arXiv2017

A spincaloritronic battery

The thermoelectric performance of a topological energy converter is analyzed. The H-shaped device is based on a combination of transverse topological effects involving the spin: the inverse spin Hall effect and the spin Nernst effect. The device can convert a temperature drop in one arm into an electric power output in the other arm. Analytical expressions for the output voltage, the figure-of-merit (ZT) and energy converting efficiency are reported. We show that the output voltage and the ZT can be tuned by the geometry of the device and the physical properties of the material. Importantly, contrary to a conventional thermoelectric device, here a low electric conductivity may in fact enhance the ZT value, thereby opening a path to new strategies in optimizing the figure-of-merit.

physics.app-ph↗