Quantum-metric-nematicity induced Kerr-like polarization rotation without time-reversal symmetry breaking

Abstract

The magneto-optic Kerr effect (MOKE), which describes the rotation and ellipticity of linearly polarized light upon reflection, is conventionally associated with time-reversal symmetry breaking. Here, we theoretically demonstrate that a Kerr-like polarization rotation can emerge even in nonmagnetic systems with time-reversal symmetry, owing to the nontrivial quantum metric of electronic bands. We show that the nematicity of the quantum metric, which captures the anisotropy of the quantum metric tensor due to the breaking of $n$-fold (with $n \ge 3$) rotational symmetry, gives rise to an incident-polarization-dependent reflected-polarization rotation. Notably, this mechanism requires neither magnetic order nor spin-orbit coupling, which are conventionally considered essential for MOKE. We illustrate the effect using a minimal tight-binding model and a model for strained MoS$_2$. This work reveals a quantum-geometric origin of the polarization rotation effects beyond conventional MOKE and suggests a new experimental approach to detect quantum metric nematicity.