Discovery of orbital-selective Cooper pairing in FeSe
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The superconductor FeSe is of intense interest thanks to its unusual non-magnetic nematic state and potential for high temperature superconductivity. But its Cooper pairing mechanism has not been determined. Here we use Bogoliubov quasiparticle interference imaging to determine the Fermi surface geometry of the bands surrounding the Γ = (0,0) and X=(π/aFe, 0) points of FeSe, and to measure the corresponding superconducting energy gaps. We show that both gaps are extremely anisotropic but nodeless, and 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 which, in FeSe, is based preferentially on electrons from the dyz orbitals of the iron atoms.
Sprau , P O , Kostin , A , Kreisel , A , Böhmer , A E , Taufour , V , Canfield , P C , Mukherjee , S , Hirschfeld , P J , Andersen , B M & Davis , J C S 2017 , ' Discovery of orbital-selective Cooper pairing in FeSe ' Science , vol 357 , no. 6346 , pp. 75-80 . DOI: 10.1126/science.aal1575
© 2017, the Author(s). This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1126/science.aal1575
For movie S1, see http://www.physik.uni-leipzig.de/~kreisel/oscp/S1.mp4, for movie S2, see http://www.physik.uni-leipzig.de/~kreisel/oscp/S2.mp4 and for movie S3, see http://www.physik.uni-leipzig.de/~kreisel/oscp/S3.mp4 Funding: Moore Foundation’s EPiQS Initiative through Grant GBMF4544 (JCSD)
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