Quadratic Optical Responses in a Chiral Magnet

TL;DR

This paper investigates quadratic optical responses in chiral magnets with conical magnetic order, revealing large effects like photovoltaic and second harmonic generation that depend on magnetic and optical parameters, with potential device applications.

Contribution

It provides a systematic analysis of nonlinear optical responses in chiral magnets using second-order response theory, highlighting their dependence on magnetic and optical conditions and their potential for technological use.

Findings

Photovoltaic effect and second harmonic generation are induced by asymmetric band modulation.

Response coefficients vary significantly with frequency, magnetic field, and spin-charge coupling.

Responses are substantially larger than in nonmagnetic materials.

Abstract

Chiral magnets, which break both spatial inversion and time reversal symmetries, carry a potential for quadratic optical responses. Despite the possibility of enhanced and controlled responses through the magnetic degree of freedom, the systematic understanding remains yet to be developed. We here study nonlinear optical responses in a prototypical chiral magnetic state with a one-dimensional conical order by using the second-order response theory. We show that the photovoltaic effect and the second harmonic generation are induced by asymmetric modulation of the electronic band structure under the conical magnetic order, and the coefficients, including the sign, change drastically depending on the frequency of incident lights, the external magnetic field, and the strength of spin-charge coupling. We find that both effects can be enormously large compared to those in the conventional nonmagnetic materials. Our results would pave the way for next-generation optical electronic devices, such as unconventional solar cells and optical sensors, based on chiral magnets.