Unidirectional perfect absorption induced by chiral coupling in spin-momentum locked waveguide magnonics
Jie Qian, Qi Hong, Ziyuan Wang, Wen Qiao Wu, Yihao Yang, C.‐M. Hu, J. Q. You, Yi‐Pu Wang
Abstract
Chiral coupling offers alternative avenues for controlling and exploiting light-matter interactions. We demonstrate that chiral coupling can be utilized to achieve unidirectional perfect absorption. In our experiments, chiral magnon-photon coupling is realized by coupling the magnon modes in yttrium iron garnet (YIG) spheres with spin-momentum-locked waveguide modes supported by spoof surface plasmon polaritons (SSPPs). These photon modes exhibit transverse spin, with the spin direction determined by the propagation direction. Due to the intrinsic spin properties of the magnon mode, it exclusively couples with microwaves traveling in one direction, effectively suppressing the reflection channel. Under the critical coupling condition, transmission is also eliminated, resulting in unidirectional perfect absorption. By incorporating additional YIG spheres, bidirectional and multi-frequency perfect absorption can be achieved. Our work introduces a functional platform for exploring and harnessing chiral light-matter interactions within spin-momentum locked devices, offering a paradigm for unidirectional signal processing and energy harvesting technologies. Introducing chirality has proved to be a fruitful method for inducing new functionalities, particularly direction-dependent properties. Here, Qian et al. realise chiral-magnon-photon coupling by combining a YIG sphere with a waveguide supporting spoof surface plasmon polaritons, allowing unidirectional transmission and perfect absorption.