Abstract:

The symmetries of superconducting gap functions remain an important issue in iron-based superconductivity. Motivated by the recent angle-resolved photoemission spectroscopic measurements of iron-chalcogenide superconductors, we investigate the constraints to the gap function symmetries from the experimental measurements on the topological surface states. The surface Dirac cone has been observed to open a gap in the superconducting phase, it implies magnetization induced from time-reversal symmetry-breaking pairing via spin-orbit coupling. Based on the crystalline symmetry constraints on the Ginzburg-Landau free energy, the gap function symmetries are among the possibilities of A1g(u) ± iA2g(u), B1g(u) ± iB2g(u), or Eg(u) ± iEg(u). This time-reversal symmetry-breaking effect can exist in the normal state very close to Tc with the relative phase between two gap functions locked at ±π/2 . This study provides the connection between the gap function symmetries and topological properties of the surface state.
Reference:
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