Condensed Matter Physics Seminar
| Date/Time: | Thursday, 20 Oct 2016 from 4:10 pm to 5:00 pm |
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| Location: | Physics 18/19 |
| Phone: | 515-294-7377 |
| Channel: | College of Liberal Arts and Sciences |
| Actions: | Download iCal/vCal | Email Reminder |
Discovery of Orbital-Selective Cooper Pairing in FeSe
FeSe is the focus of intense research interest because of its unusual non-magnetic nematic state and because it forms 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 the alpha and epsilon bands surrounding the Gamma and X points of FeSe, and to measure their superconducting energy gaps. We show directly that both gaps are extremely anisotropic but nodeless, and are aligned along orthogonal crystal axes. Moreover, by implementing a novel technique we demonstrate the sign change between the two gaps. This complex configuration of the alpha and epsilon gaps, which was unanticipated within 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. This new paradigm of orbital-selectivity may be pivotal to understanding the interplay of magnetic/nematic order and high temperature superconductivity.