arXiv subjects

Lidong Zhang

Publications and source records attributed to Lidong Zhang.

6 recordsLinked to original sources

arXiv2026

Controllable charge-spin conversion in sliding multiferroic metal Fe3GaTe2

Controlling charge--spin conversion within a single magnetic material is important for compact spintronic devices. Using first-principles calculations, symmetry analysis, and Wannier-based linear response, we study the Edelstein and spin Hall responses of sliding-ferroelectric bilayer \ce{Fe3GaTe2}. Two degenerate ground states with opposite interlayer sliding vectors and out-of-plane dipole moments are separated by a calculated switching barrier of about $16.3$~meV per unit cell. Magnetization orientation determines the allowed current-induced spin components, while ferroelectric switching induces component-selective sign reversals governed by $M_z\mathcal T$ for in-plane magnetization and by $M_z$ for out-of-plane magnetization. The Edelstein response is strongly energy dependent, with spin accumulation approaching $2~\hbar$ for $\mathbf m\parallel+y$ under a reference field of $1$~V/Å. Momentum-resolved analysis links the TR-even and TR-odd Edelstein responses to $Γ$-centered constant-energy contours and localized interband features, respectively. Spin-conductivity contributions show the opposite momentum-space character, with broad sign-competing spin Berry curvature for TR-even and narrow Fermi-surface contours for TR-odd. The transverse spin Hall conductivity reaches $\sim10^{3}\,(\hbar/e)(\mathrm{S/cm})$ and depends strongly on ferroelectric state and magnetization direction. Magnetization rotations in the $xy$ and $xz$ planes reveal symmetry-allowed higher angular harmonics in both spin accumulation and spin-current responses. These results establish sliding-ferroelectric bilayer \ce{Fe3GaTe2} as a tunable platform for reconfigurable spin accumulation and spin-current generation.

cond-mat.str-el↗

arXiv2026

Edelstein Effect in Ferromagnetic Monolayers Fe3GaTe2 and Fe3GeTe2

The Edelstein effect enables intrinsic current-induced spin polarization in noncentrosymmetric van der Waals magnets. Here, we compare the Edelstein responses of monolayer \ce{Fe3GaTe2} and \ce{Fe3GeTe2} using first-principles Wannier-based linear-response calculations. Despite sharing the same noncentrosymmetric $D_{3h}$ symmetry and selection rules, the two materials show markedly different time-reversal-even and -odd spin accumulations in magnitude, sign, and energy dependence. Strong responses occur mainly near $-0.4$~eV in \ce{Fe3GaTe2} and $+0.4$~eV in \ce{Fe3GeTe2}. At the intrinsic Fermi level, atom-resolved analysis shows that Ga-to-Ge substitution reverses the even contribution of the inequivalent Fe3 site for both in-plane magnetization directions and enhances its negative odd contribution, reorganizing the cancellation among atomic sites. Momentum-resolved calculations link the hole-side response of \ce{Fe3GaTe2} to a few large $Γ$-centered Fermi contours, whereas the electron-side response of \ce{Fe3GeTe2} involves dense Fe-$3d$ bands with strong interband contributions. The even response arises from incomplete cancellation of opposite-sign intraband Fermi-surface contributions, while the odd response originates from interband coherence between closely spaced states. Magnetization rotation reveals symmetry-constrained angular dependences with higher-order harmonics, especially in the $xz$ plane, while biaxial strain causes substantial amplitude changes and sign reversals. These results show how crystal symmetry, electronic structure, magnetization orientation, and lattice deformation govern the intrinsic Edelstein effect in \ce{Fe3$X$Te2} ($X=\mathrm{Ga},\mathrm{Ge}$).

cond-mat.mtrl-sci↗

arXiv2026

Revisiting Voltage and Synchronization Stability Analysis in Grid-Following Converter-Integrated Weak Grids: Insights from Non-Minimum-Phase Zeros

The increasing penetration of grid-following (GFL) converter-interfaced generators (CIGs) intensifies concerns over small-signal voltage and synchronization stability. While existing theories treat these two stability issues distinctly, practical wisdom in contrast employs a unified and static metric, short-circuit ratio (SCR), to assess both in weak grids. This paper aims to bridge this theory-practice gap by introducing the insight of non-minimum-phase (NMP) zeros. First, we demonstrate that the two stability issues in weak grids can be characterized within a common NMP-zero-based assessment framework: a zero at the origin corresponds to voltage instability, while low-frequency zeros impose fundamental constraints on synchronization dynamics. The traditional SCR is proven to be a special case of our proposed novel stability metric, NMP-zero (NMP-Z) factor, evaluated at the rated operating point. This establishes the theoretical foundation for the empirical success of SCR. Building on this insight, we then develop a unified stability assessment method for multi-converter systems. The method retains the simplicity of SCR, requiring only the NMP-Z factor together with individual CIG dynamic models and enabling stability margin assessment under various operating points. Our work provides a simple yet theoretically rigorous framework for stability analysis in CIG-integrated weak grids, with all theoretical findings and the proposed method validated through detailed time-domain simulations.

eess.SY↗

arXiv2025

A class of quadratic reflected BSDEs with singular coefficients

In this paper, we study the existence and uniqueness of the solution to a reflected backward stochastic differential equation (RBSDE) with the generator $g(t,y,z)=G_f^F(t,y,z)+f(y)|z|^2$, where $f(y)$ is a locally integrable function defined on an open interval $D$, and $G_f^F(t,y,z)$ is induced by $f$ and a Lipschitz continuous function $F$. Both the solution $Y_t$ and the obstacle $L_t$ of this RBSDE take values in $D$. As applications, we provide a probabilistic interpretation of an obstacle problem for a quadratic PDE with a singular term, whose solution takes values in $D$, and study an optimal stopping problem for the payoff of American options under general utilities.

math.PR↗

arXiv2021

On the backward stochastic differential equation with generator $f(y)|z|^2$

In this paper, we consider the backward stochastic differential equation (BSDE) with generator $f(y)|z|^2,$ where the function $f$ is defined on an open interval $D$ and locally integrable. The existence and uniqueness of bounded solutions and $L^p(p\geq1)$ solutions of such BSDEs are obtained. Some comparison theorems and a converse comparison theorem of such BSDEs are established. As an application, we give a probabilistic interpretation of viscosity solution of quadratic PDEs.

math.PR↗

arXiv2001

Photon Correlation Spectroscopy of a Single Quantum Dot

We report photon correlation measurements that allow us to observe unique signatures of biexcitons in a single self-assembled InAs quantum dot. Photon correlation measurements of biexciton emission exhibit both bunching and antibunching under continuous-wave excitation while only antibunching is observed under pulsed excitation. Cross-correlation between biexciton and single-exciton peaks reveal highly asymmetric features, demonstrating that biexciton and exciton emissions have strong correlations due to cascaded emission. The anticipated correlation between the polarization of exciton and biexciton emissions however, is absent under our excitation conditions. Photon correlation measurements also provide evidence for the identification of the charged exciton emission.

cond-mat↗