Multiband superconductivity in BiS₂-based layered compounds

Abstract

A mean-field treatment is presented of a square lattice two-orbital-model for [Formula: see text] taking into account intra- and inter-orbital superconductivity. A rich phase diagram involving both types of superconductivity is presented as a function of the ratio between the couplings of electrons in the same and different orbitals ([Formula: see text]) and electron doping x. With the help of a quantity we call orbital-mixing ratio, denoted as [Formula: see text], the phase diagram is analyzed using a simple and intuitive picture based on how [Formula: see text] varies as electron doping increases. The predictive power of [Formula: see text] suggests that it could be a useful tool in qualitatively (or even semi-quantitatively) analyzing multiband superconductivity in BCS-like superconductors.

Anisotropic two-gap superconductivity and the absence of a Pauli paramagnetic limit in single-crystalline LaO0.5F0.5BiS2

“…These gaps could be responsible for the two-gap physics we discussed above. A recent calculation discusses the possibility of having two different gaps on a single Fermi surface sheet, and shows that the gaps are connected to the variation of orbital mixing along the Fermi surface sheet [57]. However, thermal conductivity [58] and penetration depth [59] measurements on the same Nd-based systems did not detect the existence of the gap nodes.…”

Impurity Effects in Nodal Extendeds- and Nodelessd-Wave Superconductors: Gap Symmetry of BiS2-Based Layered Superconductors

“…35) The gap anisotropy in BiS 2 -based layered materials has been discussed in the context of multiorbital superconductivity. 36,37) In this paper, we have not included orbital degrees of freedom in the impurity scattering, but the gap state is considered to be affected, more or less, by the nonmagnetic impurity scattering even in multiorbital superconductors, when the gap has nodes on the Fermi-surface curve or the sign is reversed between the gaps on the different Fermi-surface curves. Thus, we believe that the impurity effect is also useful for the determination of the gap symmetry of multiorbital superconductors, although it is necessary to develop carefully the discussion on the nonmagnetic impurity scattering in multi-orbital superconductors from a quantitative viewpoint.…”