Nonreciprocal spin waves driven by left-hand microwaves

It is a conventional wisdom that left-hand microwave cannot efficiently excite the spin wave (SW) in ferromagnets, due to constraint of angular momentum conservation. In this work, we show can drive nonreciprocal SWs presence strong ellipticity-mismatch between and precessing magnetization. A critical frequency predicted, at which SWs. Away from it SW amplitude sensitively depends on ellipticity microwaves, sharp contrast case driven by right-hand ones. By tuning frequency, observe switchable non-reciprocity ferromagnetic single layer. mode-dependent mutual demagnetizing factor proposed explain finding. Our work advances understanding photon-magnon conversion, paves way designing diode-like functionalities nano-scaled magnonics.