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Observation of strong electron pairing on bands without Fermi surfaces in LiFe(1-x) CoxAs

DOI: 10.1038/ncomms7056 DOI Help
PMID: 25583450 PMID Help

Authors: H. Miao (Chinese Academy of Sciences) , T. Qian (Chinese Academy of Sciences) , X. Shi (Chinese Academy of Sciences) , P. Richard (Institute of Physics, Chinese Academy of Sciences) , T. Kim (Diamond Light Source) , M. Hoesch (Diamond Light Source) , L. Y. Xing (Chinese Academy of Sciences) , X- C Wang (Chinese Academy of Sciences) , C- Q Jin (Chinese Academy of Sciences) , J- P Hu (Chinese Academy of Sciences) , H. Ding (Chinese Academy of Sciences)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature Communications , VOL 6

State: Published (Approved)
Published: January 2015
Diamond Proposal Number(s): 9469

Abstract: In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still valid in high-Tc superconductors such as cuprates and iron-based superconductors remains an open question. In particular, a fundamentally different picture of the electron pairs, which are believed to be formed locally by repulsive interactions, may prevail. Here we report a high-resolution angle-resolved photoemission spectroscopy study on LiFe (1-x)CoxAs. We reveal a large and robust superconducting gap on a band sinking below the Fermi level on Co substitution. The observed Fermi-surface-free superconducting order is also the largest over the momentum space, which rules out a proximity effect origin and indicates that the order parameter is not tied to the Fermi surface as a result of a surface instability.

Subject Areas: Physics

Instruments: I05-ARPES