Heun’s equation and analytic structure of the gap in holographic superconductivity Yoon-Seok Choun, Wenhe Cai and Sang-Jin Sin Eur. Phys. J. C, 82 5 (2022) 402 Published online: 04 May 2022 DOI: 10.1140/epjc/s10052-022-10294-0