Nonlinear optical diode effect in a magnetic Weyl semimetal

TL;DR

This paper reports the first experimental observation of a nonlinear optical diode effect in a magnetic Weyl semimetal, demonstrating broadband nonreciprocal second-harmonic generation controlled by magnetization and electrical switching.

Contribution

It provides the first experimental evidence of a broadband nonlinear optical diode effect in a magnetic Weyl semimetal, linking Weyl fermions to nonreciprocal optical phenomena.

Findings

Six-fold change in SHG intensity between opposite directions

Broadband effect exceeding 250 meV bandwidth

Electrical control of the nonlinear optical diode effect

Abstract

Diode effects are of great interest for both fundamental physics and modern technologies. Electrical diode effects (nonreciprocal transport) have been observed in Weyl systems. Optical diode effects arising from the Weyl fermions have been theoretically considered but not probed experimentally. Here, we report the observation of a nonlinear optical diode effect (NODE) in the magnetic Weyl semimetal CeAlSi, where the magnetization introduces a pronounced directionality in the nonlinear optical second-harmonic generation (SHG). We show demonstrate a six-fold change of the measured SHG intensity between opposite propagation directions over a bandwidth exceeding 250 meV. Supported by density-functional theory, we establish the linearly dispersive bands emerging from Weyl nodes as the origin of this broadband effect. We further demonstrate current-induced magnetization switching and thus electrical control of the NODE. Our results advance ongoing research to identify novel nonlinear optical/transport phenomena in magnetic topological materials and further opens new pathways for the unidirectional manipulation of light.