Discovery of orbital-selective Cooper pairing in FeSe

P O Sprau; A Kostin; A Kreisel; A E Böhmer; V Taufour; P C Canfield; S Mukherjee; P J Hirschfeld; B M Andersen; J C Séamus Davis

doi:10.1126/science.aal1575

Discovery of orbital-selective Cooper pairing in FeSe

Science. 2017 Jul 7;357(6346):75-80. doi: 10.1126/science.aal1575.

Authors

P O Sprau^{1

2}, A Kostin^{1

2}, A Kreisel^{3

4}, A E Böhmer⁵, V Taufour⁵, P C Canfield^{5

6}, S Mukherjee⁷, P J Hirschfeld⁸, B M Andersen³, J C Séamus Davis^{9

2

10

11}

Affiliations

¹ Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853, USA.
² Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
³ Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK 2100 Copenhagen, Denmark.
⁴ Institut für Theoretische Physik, Universität Leipzig, D-04103 Leipzig, Germany.
⁵ Ames Laboratory, U.S. Department of Energy, Ames, IA 50011, USA.
⁶ Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
⁷ Department of Physics, Binghamton University-State University of New York, Binghamton, NY, USA.
⁸ Department of Physics, University of Florida, Gainesville, FL 32611, USA.
⁹ Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853, USA. jcseamusdavis@gmail.com.
¹⁰ School of Physics and Astronomy, University of St Andrews, Fife KY16 9SS, Scotland.
¹¹ Tyndall National Institute, University College Cork, Cork T12R5C, Ireland.

PMID: 28684522
DOI: 10.1126/science.aal1575

Abstract

The superconductor iron selenide (FeSe) is of intense interest owing to its unusual nonmagnetic nematic state and potential for high-temperature superconductivity. But its Cooper pairing mechanism has not been determined. We used Bogoliubov quasiparticle interference imaging to determine the Fermi surface geometry of the electronic bands surrounding the Γ = (0, 0) and X = (π/a_Fe, 0) points of FeSe and to measure the corresponding superconducting energy gaps. We show that both gaps are extremely anisotropic but nodeless and that they exhibit gap maxima oriented orthogonally in momentum space. Moreover, by implementing a novel technique, we demonstrate that these gaps have opposite sign with respect to each other. This complex gap configuration reveals the existence of orbital-selective Cooper pairing that, in FeSe, is based preferentially on electrons from the d _yz orbitals of the iron atoms.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.