Nonreciprocal Directional Dichroism Induced by the Quantum Metric Dipole

TL;DR

This paper reveals that the quantum metric dipole is the geometric origin of nonreciprocal directional dichroism, linking it to quadrupolar transport and spectral features, with implications for understanding optical phenomena.

Contribution

It identifies the quantum metric dipole as the geometric basis for nonreciprocal directional dichroism and explores its effects at static and finite frequencies.

Findings

Quantum metric dipole causes nonreciprocal directional dichroism.

Steepest slope of quantum metric dipole determines spectral peaks.

Features demonstrated in a low-energy model.

Abstract

We identify the quantum metric dipole as the geometric origin of the nonreciprocal directional dichroism which describes the change in the refractive index upon reversing the light propagation direction. Specifically, we find that the static limit of the nonreciprocal directional dichroism corresponds to a quadrupolar transport current from the quantum metric dipole, in response to a quadrupolar electric field. Moreover, at finite frequency, we demonstrate that the steepest slope of the averaged quantum metric dipole determines a peak. Finally, we illustrate both features in a low-energy model.