Abstract
The microscopic mechanism governing the zero-resistance flow of current in some iron-based, high-temperature superconducting materials is not well understood up to now. A central issue concerning the investigation of these materials is their superconducting gap symmetry and structure. Here we present a combined study of low-temperature specific heat and scanning tunnelling microscopy measurements on single crystalline FeSe. The results reveal the existence of at least two superconducting gaps which can be represented by a phenomenological two-band model. The analysis of the specific heat suggests significant anisotropy in the gap magnitude with deep gap minima. The tunneling spectra display an overall “U”-shaped gap close to the Fermi level away as well as on top of twin boundaries. These results are compatible with the anisotropic nodeless models describing superconductivity in FeSe.
Highlights
Soon after the discovery of the Fe-based superconductors (Fe-SC) great effort has been devoted to unveil their electron paring mechanism
A central issue concerning the investigation of these materials is their superconducting gap symmetry and structure
Owing to the marked dependence of the superconducting properties even for FeSe samples grown by the same method [24, 25], concerted investigations on identical single crystals are required to establish one of its most fundamental properties, viz., the symmetry of the superconducting order parameter
Summary
Soon after the discovery of the Fe-based superconductors (Fe-SC) great effort has been devoted to unveil their electron paring mechanism. In order to resolve this issue, it is necessary to perform both bulk and surface sensitive experiments on FeSe. Owing to the marked dependence of the superconducting properties even for FeSe samples grown by the same method [24, 25], concerted investigations on identical single crystals are required to establish one of its most fundamental properties, viz., the symmetry of the superconducting order parameter. We report on specific heat C(T ) combined with low-temperature (T ≥ 0.35 K) scanning tunnelling microscopy (STM) measurements on a stoichiometric FeSe single crystal to establish its superconducting order parameter As shown below, such a combination of techniques, bulk sensitive C(T ) and surface sensitive STM, allows us to unequivocally resolve the superconducting gap structure of FeSe to be nodeless
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