It is a conventional wisdom that a left-hand microwave cannot efficiently excite the spin wave (SW) in ferromagnets, due to the constraint of angular momentum conservation. In this work, we show that the left-hand microwave can drive nonreciprocal SWs in the presence of a strong ellipticity-mismatch between the microwave and precessing magnetization. A critical frequency is predicted, at which the left-hand microwave cannot excite SWs. Away from it the SW amplitude sensitively depends on the ellipticity of left-hand microwaves, in sharp contrast to the case driven by right-hand ones. By tuning the microwave frequency, we observe a switchable SW non-reciprocity in a ferromagnetic single layer. A mode-dependent mutual demagnetizing factor is proposed to explain this finding. Our work advances the understanding of the photon-magnon conversion, and paves the way to designing diode-like functionalities in nano-scaled magnonics.
@article{arxiv.2202.00780,
title = {Nonreciprocal Spin Waves Driven by Left-Hand Microwaves},
author = {Zhizhi Zhang and Zhenyu Wang and Huanhuan Yang and Z. -X. Li and Yunshan Cao and Peng Yan},
journal= {arXiv preprint arXiv:2202.00780},
year = {2022}
}