Abstract
A variety of superconducting materials exhibit multi-band behavior in a form of multicomponent Fermi surfaces. By using a two-band model with a pair hopping, we explain how the interband coupling affects the physical properties of multi-band superconductors. We determine the temperature dependence of the superconducting gap and the specific heat, which strongly diverge from the BCS-type behavior. The anisotropic gap for the system with the mixed gap symmetry is found. Additionally, the spectral function and density of states are significantly modified by the inter-orbital interactions. The results obtained for different symmetries of the order parameter are in a good agreement with the experimental findings for the iron-based superconductors and other multi-band systems.
Highlights
The discovery of superconductivity in multi-band materials opened a period of intensive studies of these systems [1, 2]
The calculations have been performed in the momentum space using a square lattice grid kx × ky = 300 × 300 and periodic boundary conditions, with the help of the graphic processor unit (GPU) acceleration described in [45]
We present and discuss the temperature dependence of the gaps and specific heat. In these sections we chose the s±-wave gap symmetry in both bands, what corresponds to the standard assumption for the iron-based superconductors
Summary
The discovery of superconductivity in multi-band materials opened a period of intensive studies of these systems [1, 2]. As a consequence of multi-band properties one can observe several order parameters of different magnitude [5, 6]. The Fermi surfaces and characteristic band structure of the iron-based superconductors are the consequences of the layered structure of these compounds. The conventional multi-band BCS-type and iron-based superconductors differ in their symmetry of the order parameter. In nearly magnetic Fe-based layered systems mediated by antiferromagnetic spin fluctuations, the s± symmetry with a sign reversal of the order parameter between different Fermi surface sheets can be favored [13, 30]. The unconventional properties are observed experimentally [31], e.g., in the measurements of energy gap or specific heat These observations can provide the information about the effective interactions in each band and the symmetry of the order parameter.
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