Surface-Dominated Quantum-Metric-Induced Nonlinear Transport in the Layered Antiferromagnet CrSBr.

The van der Waals (vdW) antiferromagnet CrSBr has recently garnered significant attention due to its air stability, high magnetic transition temperature, and semiconducting properties. We investigate its nonlinear transport properties and identify a quantum-metric-dipole (QMD)-induced nonlinear anomalous Hall effect and nonlinear longitudinal resistivity, which switch signs upon reversing the Néel vector. The significant QMD originates from Dirac nodal lines near the conduction band edge within the experimentally achievable doping range. Knowing the weak interlayer coupling, it is unexpected that the nonlinear conductivities do not scale with the sample thickness but are dominantly contributed by surface layers. In the electron-doped region, the top layer dominates the response, while the top three layers contribute the most in the hole-doped region. Our results establish topological nodal lines as a guiding principle to design high-performance nonlinear quantum materials, and we suggest that surface-sensitive transport devices will provide new avenues for nonlinear electronic applications.