Nonreciprocal optical response in parity-breaking superconductors

TL;DR

This paper predicts that superconductors lacking inversion symmetry exhibit giant nonreciprocal optical effects, such as photocurrent and second harmonic generation, especially at low frequencies, due to unique parity-breaking indicators.

Contribution

It introduces the concept of nonreciprocal superfluid density and Berry curvature derivative as key indicators for nonreciprocal optical responses in parity-breaking superconductors.

Findings

Nonreciprocal responses diverge at low frequencies.

Indicators quantify nonreciprocal optical performance.

Mechanisms depend on preserved temporal symmetry.

Abstract

Superconductivity, an emergence of a macroscopic quantum state, gives rise to unique electromagnetic responses leading to perfect shielding of magnetic field and zero electrical resistance. In this paper, we propose that superconductors with the space-inversion symmetry breaking host giant nonreciprocal optical phenomena, such as photocurrent generation and second harmonic generation. The nonreciprocal optical responses show divergent behaviors in the low-frequency regime and originate from two-fold indicators unique to parity-breaking superconductors, namely, the nonreciprocal superfluid density and the Berry curvature derivative. Furthermore, the mechanism and frequency dependence are closely tied to the preserved temporal symmetry in the superconductor. The relation is useful for probing the space-time structure of the superconducting symmetry. The indicators characterize the low-frequency property of nonreciprocal optical responses and hence quantify the performance of superconductors in nonreciprocal optics.