Refractive index in generalized superconductors with Born–Infeld electrodynamics Jun Cheng, Qiyuan Pan, Hongwei Yu and Jiliang Jing Eur. Phys. J. C, 78 3 (2018) 239 Published online: 21 March 2018 DOI: 10.1140/epjc/s10052-018-5729-9