Nonlinear optical nonreciprocity in a surface plasmon–exciton coupled asymmetric cavity systemShengfa Fan, Fengxue Zhou, Fei Xu, Yihong Qi, Yueping Niu and Shangqing GongEur. Phys. J. D, 76 11 (2022) 212DOI: https://doi.org/10.1140/epjd/s10053-022-00541-0