Observation of the Magnus Nonlinear Hall effect from Chiral Weyl Monopoles

TL;DR

This paper reports the observation of the nonlinear Hall effect in the chiral Weyl semimetal CoSi, revealing a Berry monopole-driven nonlinear transport mechanism linked to topological band features.

Contribution

It demonstrates the first experimental detection of the nonlinear Hall effect in a high-symmetry chiral lattice, highlighting a skew-scattering mechanism related to Berry monopoles.

Findings

Robust second-harmonic Hall voltage observed in CoSi

NLHE signal shows temperature-dependent sign reversal

NLHE modulated linearly by magnetic field and carrier mobility

Abstract

The nonlinear Hall effect (NLHE) connects crystalline symmetry to quantum geometry, offering a probe of band topology beyond linear transport. While most studies have focused on the Berry curvature dipole in low-symmetry crystals, mechanisms that directly probe Berry monopoles in higher-symmetry chiral lattices remain unexplored. Here, we report the observations of the NLHE in the chiral Weyl semimetal CoSi, a platform where the Berry curvature dipole is symmetry-forbidden. By employing focused ion beam-fabricated crossbar devices, we detect a robust second-harmonic Hall voltage under zero magnetic field, hosting all key signatures of the NLHE. Theoretical analysis attributes the nonlinear Hall conductivity to skew scattering of self-rotating electron wave packets, whose chirality is dictated by the underlying band topology, a process reminiscent of the classical Magnus effect. Furthermore, the NLHE signal exhibits a temperature-dependent sign reversal, and a strong, linearly field-dependent modulation that grows with carrier mobility, directly reflecting the topological Weyl nodes distribution near the Fermi level. These findings establish CoSi as a platform for Berry monopole-driven nonlinear transport, demonstrating a skew-scattering route to topological nonlinear Hall responses that bypasses conventional symmetry constraints.