Dyonic Reissner–Nordstrom black holes and superradiant stability Yi-Feng Zou, Jun-Huai Xu, Zhan-Feng Mai and Jia-Hui Huang Eur. Phys. J. C, 81 9 (2021) 855 Published online: 29 September 2021 DOI: 10.1140/epjc/s10052-021-09642-3