Speaker: Christian Tzschaschel (University of Zurich)

Weyl semimetals have emerged as a promising quantum material system to discover novel electrical and optical phenomena, due to their combination of nontrivial quantum geometry and strong symmetry breaking. Here, I will present the observation of the nonlinear optical diode effect (NODE) in the magnetic Weyl semimetal CeAlSi, where the magnetic state of CeAlSi introduces a pronounced directionality in the nonlinear optical second-harmonic generation (SHG). By physically reversing the beam path, we show that the measured SHG intensity can change by at least a factor of six between forward and backward propagation over a wide bandwidth exceeding 250 meV. Supported by density-functional theory calculations, we establish the linearly dispersive bands emerging from Weyl nodes as the origin of the extreme bandwidth. By utilizing the electronically conductive semimetallic nature of CeAlSi, we demonstrate current-induced magnetization switching and thus electrical control of the NODE in a mesoscopic spintronic device structure. Our results advance ongoing research to identify novel nonlinear optical/transport phenomena in magnetic topological materials. The NODE further opens new pathways for the unidirectional manipulation of light such as electrically controlled optical isolators [1].

[1] CT et al., Nature Communications 15, 3017 (2024)