Suheel Ahmad Malik | Searcharxiv

arXiv2026

Persistent nonlinear Hall effect driven by parallel field across a topological phase transition and intraband sign-reversing integer quantum Hall effect

We investigate the linear and nonlinear Hall effects in a two-dimensional Rashba spin-orbit coupled nodal ring electronic system. We consider both the cases of linear Hall effect, the Berry curvature induced anomalous Hall and the perpendicular magnetic field-induced integer quantum Hall effect. We observe that the system exhibits a topological gap along the boundary of the nodal ring that strongly depends on the radius of the nodal ring and the strength of the Rashba spin-orbit interaction, resulting in the quantum anomalous Hall effect. Subsequently, we include a perpendicular uniform magnetic field and obtain the exact Landau levels that exhibit sign reversal in the slope with magnetic field around the ring boundary. This causes a sign reversal in the quantum Hall conductivity in the same band by tuning the magnetic field. Most importantly, we also show that when the magnetic field is strictly parallel to the system, it can induce an anisotropy to the Berry curvature that leads to the emergence of the nonlinear Hall effect. Additionally, tuning the parallel field can close and reopen the topological gap, resulting in the reverse topological phase transition from the topological Chern insulator to a trivial insulator. The nonlinear Hall effect remains persistent in both phases, but its dependence on the chemical potential exhibits distinct signatures. Noticeably, the nonlinear Hall response exhibits a sign-changing peak structure in Chern insulating phase whereas it displays a single-sign response in trivial insulating phase. These distinct signatures suggest that nonlinear Hall can serve as a probe to study such a topological phase transition.

cond-mat.mes-hall↗

arXiv2026

Probing imbalanced Weyl nodes in two-dimensional anisotropic Weyl semimetal via optical conductivity

We present a theoretical investigation of the electronic band structure and optical properties of a two-dimensional anisotropic semimetal that is described by a tilted semi-Dirac type spectrum with a pair of Weyl nodes. We observe that a tilt along the quadratic direction can give rise to an energy imbalance between these nodes, contrary to the effect of tilt along the linear direction. We investigate the optical response of such system subjected to an external AC bias, aiming to probe the energy imbalance between the nodes. We show that the anisotropic interband optical conductivity gives a clear signature of imbalanced nodes by exciting electrons at two different chemical potentials at near zero frequency and the difference between these two chemical potentials is the direct measure of the energy imbalance. Subsequently, we also investigate the intraband DC conductivity by using the semi-classical Boltzmann transport theory which reveals that contrary to the tilted Dirac materials, tilt can convert semi-Dirac material from semimetallic phase to metallic phase. Furthermore, we periodically drive the system by external time-periodic perturbation to open up topological gap at those nodes. We also show that the presence of imbalanced Weyl nodes would prevent the semi-Dirac material from switching to Chern topological phase even after opening topological gaps at the nodes as the bulk remains gapless. Such state cannot be probed by the usual anomalous Hall response, as it will be overshadowed by the bulk contribution. Here, we show that those gaps at different chemical potentials can be probed by optical excitation. Finally, we extend our study to nonlinear regime, where we particularly focus on second harmonic generation in an inversion symmetry broken tilted semi-Dirac system. A clear signature of energy imbalanced Weyl nodes can also be detected here.

cond-mat.mes-hall↗