arXiv subjects

Xin-Zhi Li

Publications and source records attributed to Xin-Zhi Li.

5 recordsLinked to original sources

arXiv2025

Orbital magnetization as the origin of the nonlinear Hall effect

The nonlinear Hall effect is a new type of Hall effect that has recently attracted significant attention. For the physical origin of the nonlinear Hall effect, while orbital magnetization has long been hypothesized to underpin the nonlinear Hall effect, a general relation between the two quantities remains elusive. Here, we resolve the problem by deriving the first explicit formula connecting the electric field induced orbital magnetization to the second order Hall conductivity. Our theory reveals that the applied electric field plays dual roles in generating the nonlinear Hall effect: it first generates nonequlibrium orbital magnetization associated with an edge current, and subsequently perturbs the circulating edge states to produce transverse Hall voltage. For the experimental verification, we propose to apply a combination of direct and alternative currents to identify the circulating edge current in the nonlinear Hall effect. Based on the orbital magnetization origin, we point out that in isotropic chiral metals of T and O point groups, the crystalline symmetry suppresses the nonlinear Hall response for a monochromatic linear polarized electric field, but a non-collinear bichromatic electric field can generate a finite nonlinear Hall current that manifests the chiral correlation of the field. This discovery finally enables us to incorporate both the nonlinear Hall effect and circular photo-galvanic effect into the framework of orbital magnetization.

cond-mat.mes-hall↗

arXiv2025

Ferroelectric Hysteresis in Superconducting Bilayers

Recently, coexisting ferroelectricity and superconductivity were reported in bilayer T$_{\textrm{d}}$-MoTe$_2$ and twisted bilayer graphene. Importantly, it was observed that an applied displacement field switches the superconductivity with a ferroelectric hysteresis. Such direct coupling between the ferroelectricity and superconductivity offers promising pathways for developing low-power, non-volatile memory devices. However, the coupling mechanism between the ferroelectricity and superconductivity remains poorly understood. In this work, we demonstrate that in a superconducting bilayer, the hysteretic switching of superconductivity can arise from an interlayer pairing. By deriving the Landau Ginzburg free energy expansion for the interlayer pairing, we show that along the ferroelectric hysteresis loop, the hysteretic exceeding of the critical polarization $P_{\textrm{c}}$ that destroys the interlayer pairing leads to the hysteretic switching of superconductivity. The condition to have a ferroelectric hysteretic superconducting state is established to be $P_{\textrm{r}}<P_{\textrm{c}}<P_{\textrm{s}}$, where $P_{\textrm{r}}$ and $P_{\textrm{s}}$ denote the remanent and saturated polarization, respectively. Crucially, our scenario of interlayer pairing yields two predictions: (1) an enhancement of the upper critical displacement field with stronger interlayer coupling and (2) a pronounced, gate-tunable interlayer crossed Andreev reflection, both of which provide clear pathways for experimental verification.

cond-mat.supr-con↗

arXiv2025

Field-Tunable Anisotropic Fulde-Ferrell Phase in NbSe$_2$/CrSiTe$_3$ Heterostructures

The emergence of superconductivity in two-dimensional transition metal dichalcogenides with strong spin orbit coupling (SOC) has opened new avenues for exploring exotic superconducting states. Here, we report experimental observation of an anisotropic Fulde-Ferrell (FF) phase in few-layer NbSe$_2$/CrSiTe$_3$ heterostructures under in-plane magnetic fields. Through combined magnetoresistance and nonreciprocal transport measurements, we find that due to the couplings from the ferromagnetic CrSiTe$_3$, a half-dome-shaped region emerges in the magnetic field-temperature ($B$-$T$) diagram. Importantly, the half-dome-shaped region exhibits finite second harmonic resistance with in-plane anisotropy, indicating that the superconducting state is an anisotropic FF phase. Through a symmetry analysis combined with mean field calculations, we attribute the emergent anisotropic FF phase to the CrSiTe$_3$ layer induced Rashba SOC and three-fold rotational symmetry breaking. These results demonstrate that heterostructure stacking is a powerful tool for symmetry engineering in superconductors, which can advance the design of quantum devices in atomically thin superconducting materials.

cond-mat.supr-con↗

arXiv2024

Selective and Quasi-continuous Switching of Ferroelectric Chern Insulator Device for Neuromorphic Computing

Topologically protected edge state transport in quantum materials is dissipationless and features quantized Hall conductance, and shows great potential in highly fault-tolerant computing technologies. However, it remains elusive about how to develop topological edge state-based computing devices. Recently, exploration and understanding of interfacial ferroelectricity in various van der Waals heterostructure material systems have received widespread attention among the community of materials science and condensed matter physics3-11. Such ferroelectric polarization emergent at the vdW interface can coexist with other quantum states and thus provides an unprecedented opportunity to electrically switch the topological edge states of interest, which is of crucial significance to the fault-tolerant electronic device applications based on the topological edge states. Here, we report the selective and quasi-continuous ferroelectric switching of topological Chern insulator devices and demonstrate its promising application in noise-immune neuromorphic computing. We fabricate this ferroelectric Chern insulator device by encapsulating magic-angle twisted bilayer graphene with doubly-aligned h-BN layers, and observe the coexistence of the interfacial ferroelectricity and the topological Chern insulating states. This ferroelectricity exhibits an anisotropic dependence on the in-plane magnetic field. By using a VBG pulse with delicately controlled amplitude, we realize the nonvolatile switching between any pair of Chern insulating states and achieve 1280 distinguishable nonvolatile resistance levels on a single device. Furthermore, we demonstrate deterministic switching between two arbitrary levels among the record-high number of nonvolatile resistance levels.

cond-mat.mes-hall↗

arXiv2024

Topological Superconductivity in Monolayer T$_{\textrm{d}}$-MoTe$_2$

Topological superconductivity has attracted significant attention due to its potential applications in quantum computation, but its experimental realization remains challenging. Recently, monolayer T$_{\textrm{d}}$-MoTe$_2$ was observed to exhibit gate tunable superconductivity, and its in-plane upper critical field exceeds the Pauli limit. Here, we show that an in-plane magnetic field beyond the Pauli limit can drive the superconducting monolayer T$_{\textrm{d}}$-MoTe$_2$ into a topological superconductor. The topological superconductivity arises from the interplay between the in-plane Zeeman coupling and the unique \emph{Ising plus in-plane SOC} in the monolayer T$_{\textrm{d}}$-MoTe$_2$. The \emph{Ising plus in-plane SOC} plays the essential role to enable the effective $p_x+ip_y$ pairing. Importantly, as the essential \emph{Ising plus in-plane SOC} in the monolayer T$_{\textrm{d}}$-MoTe$_2$ is generated by an in-plane polar field, our proposal demonstrates that applying an in-plane magnetic field to a gate tunable 2D superconductor with an in-plane polar axis is a feasible way to realize topological superconductivity.

cond-mat.supr-con↗