Dresden 2017 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 21: Focus Session: Nematicity, Magnetism and Superconductivity in FeSe and Related Compounds
TT 21.2: Invited Talk
Tuesday, March 21, 2017, 10:00–10:30, HSZ 03
Discovery of Orbital-Selective Cooper Pairing in FeSe — •J. C. Séamus Davis1, Peter Sprau2, Andrey Kostin2, Andreas Kreisel3, Anna Böhmer4, Paul Canfield4, S. Mukherjee5, Peter Hirschfeld6, and Brian Andersen7 — 1Department of Physics, Cornell University, Ithaca, NY 14853, USA. — 2Brookhaven National Laboratory, Upton, NY 11973, USA. — 3Universität Leipzig, D-04103 Leipzig, Germany — 4Ames Laboratory, U.S. Department of Energy, Ames, IA 50011, USA — 5Binghamton University - SUNY, Binghamton, USA. — 6University of Florida, Gainesville, Florida32611, USA — 7University of Copenhagen, DK 2100 Copenhagen, Denmark
FeSe is the focus of intense research interest as the basis for achieving the highest critical temperatures of any iron-based superconductor. However, its Cooper pairing mechanism has not been determined because an accurate knowledge of the momentum-space structure of superconducting energy gaps on the different electron-bands does not exist. Here we use Bogoliubov quasiparticle interference (BQPI) imaging to determine the coherent Fermi surface geometry of multiple bands, and to measure their superconducting energy gaps. We show directly that both gaps are extremely anisotropic but nodeless, and of opposite sign. This complex configuration of energy gaps which was unanticipated by existing pairing theories for FeSe, reveals a unique form of superconductivity based on orbital-selective Cooper pairing of electrons from the dyz orbitals of iron atoms.