Three-dimensional superconducting gap in FeSe from angle-resolved photoemission spectroscopy

We present a systematic angle-resolved photoemission spectroscopy study of the superconducting gap in FeSe. The gap function is determined in a full Brillouin zone including all Fermi surfaces and k(z) dependence. We find significant anisotropy of the superconducting gap in all momentum directions. While the in-plane anisotropy can be explained by both nematicity-induced pairing anisotropy and orbital-selective pairing, the k(z) anisotropy requires an additional refinement of the theoretical approaches.