arXiv subjects

Zi-Xuan Gao

Publications and source records attributed to Zi-Xuan Gao.

4 recordsLinked to original sources

arXiv2026

Linear magnetoresistance of two-dimensional massless Dirac fermions in the quantum limit

Linear magnetoresistance is a hallmark of 3D Weyl metals in the quantum limit. Recently, a pronounced linear magnetoresistance has also been observed in 2D graphene [Xin et al., Nature 616, 270 (2023)]. However, a comprehensive theoretical understanding remains elusive. By employing the self-consistent Born approximation, we derive the analytical expressions for the magnetoresistivity of 2D massless Dirac fermions in the quantum limit. Notably, our result recovers the minimum conductivity in the clean limit and reveals a linear dependence of resistivity on the magnetic field for Gaussian impurity potentials, in quantitative agreement with experiments. These findings shed light on the magnetoresistance behavior of 2D Dirac fermions under ultra-high magnetic fields.

cond-mat.mes-hall↗

arXiv2025

A Clarification on Quantum-Metric-Induced Nonlinear Transport

Over the years, Berry curvature, which is associated with the imaginary part of the quantum geometric tensor, has profoundly impacted many branches of physics. Recently, quantum metric, the real part of the quantum geometric tensor, has been recognized as indispensable in comprehensively characterizing the intrinsic properties of condensed matter systems. The intrinsic second-order nonlinear conductivity induced by the quantum metric has attracted significant recent interest. However, its expression varies across the literature. Here, we reconcile this discrepancy by systematically examining the nonlinear conductivity using the standard perturbation theory, the wave packet dynamics, and the Luttinger-Kohn approach. Moreover, inspired by the Dirac model, we propose a toy model that suppresses the Berry-curvature-induced nonlinear transport, making it suitable for studying the quantum-metric-induced nonlinear conductivity. This work provides a clearer and more unified understanding of the quantum-metric contributions to nonlinear transport. It also establishes a solid foundation for future theoretical developments and experimental explorations in this highly active and rapidly evolving field.

cond-mat.mes-hall↗

arXiv2025

Realization of chiral whispering gallery mode cavities enabled by photonic Chern insulators

Recently, whispering gallery modes (WGMs) have attracted considerable attention due to their extensive applications in the development of on-chip microcavities, high-sensitivity sensors, and high-performance lasers. Conventional WGMs are achiral under the time-reversal symmetry, and show high sensitivity to defects in optical devices. Here, we introduce topological physics into photonic cavities and demonstrate the realization of chiral WGMs enabled by photonic Chern insulators. Through comprehensive numerical simulations and experimental measurements, we reveal the critical differences between chiral and achiral WGMs, highlighting the robustness of chiral WGMs even in the presence of defects within the cavities. Our research provides valuable insights into the design of robust WGM cavities and offers a novel platform for exploring light-matter interaction phenomena.

physics.optics↗

arXiv2024

Realization of time-reversal invariant photonic topological Anderson insulators

Disorder, which is ubiquitous in nature, has been extensively explored in photonics for understanding the fundamental principles of light diffusion and localization, as well as for applications in functional resonators and random lasers. Recently, the investigation of disorder in topological photonics has led to the realization of topological Anderson insulators characterized by an unexpected disorder-induced phase transition. However, the observed photonic topological Anderson insulators so far are limited to the time-reversal symmetry breaking systems. Here, we propose and realize a photonic quantum spin Hall topological Anderson insulator without breaking time-reversal symmetry. The disorder-induced topological phase transition is comprehensively confirmed through the theoretical effective Dirac Hamiltonian, numerical analysis of bulk transmission, and experimental examination of bulk and edge transmissions. We present the convincing evidence for the unidirectional propagation and robust transport of helical edge modes, which are the key features of nontrivial time-reversal invariant topological Anderson insulators. Furthermore, we demonstrate disorder-induced beam steering, highlighting the potential of disorder as a new degree of freedom to manipulate light propagation in magnetic-free systems. Our work not only paves the way for observing unique topological photonic phases but also suggests potential device applications through the utilization of disorder.

physics.optics↗