Surface reconstruction and charge modulation in BaFe₂As₂ superconducting film

Abstract

Whether or not epitaxially grown superconducting films have the same bulk-like superconducting properties is an important concern. We report the structure and the electronic properties of epitaxially grown Ba(Fe Co )As films using scanning tunneling microscopy and scanning tunneling spectroscopy (STS). This film showed a different surface structure, [Formula: see text]R45° reconstruction, from those of as-cleaved surfaces from bulk crystals. The electronic structure of the grown film is different from that in bulk, and it is notable that the film exhibits the same superconducting transport properties. We found that the superconducting gap at the surface is screened at the Ba layer surface in STS measurements, and the charge density wave was observed at the surface in sample in the superconducting state.

ARPES detection of superconducting gap sign in unconventional superconductors

“…In the iron-based superconductors like (Ba,K)Fe 2 As 2 , in order to determine the relative gap sign between Γ and M, i.e., whether the gap symmetry is s ± or s ++ 36 – 41 , the surface reconstruction can be used to fold the bands between the Γ and M points 42 , 43 . In the case that no natural band folding mechanisms are available, it is possible to engineer the band structures to produce hybridization between the initial bands and the superstructure bands such as those realized in twisted graphene 44 – 46 or substrate-controlled film growth 47 , 48 . It should be noted that the key requirement is a perturbative periodic potential that folds the native Fermi surface and thus creates crossing points.…”