Theoretical study of the physical properties of BiS2 superconductors

Abstract

Recent angle-resolved photoemission reveals that the doping level in some BiS2-based superconductors is much lower than the nominal one. Here we determine the pairing function at such a realistic low doping level by a functional renormalization group (FRG) and study the resulting physical properties by an FRG-based effective mean field theory. We find that the pairing is a mixture of singlets and triplets due to spin-orbital coupling, and the triplet components dominate. The gap function transforms as a dx2−y2* wave under simultaneous rotation of spin and lattice, but is nodeless on the Fermi pockets which avoid the nodal lines. The specific heat, superfluid density, and Knight shift are similar to that in a fully gapped conventional s-wave superconductor, in agreement with available experiments. However, the absence of the Hebel-Slichter peak in spin-lattice relaxation rate (in the dirty limit), the impurity induced in-gap states, and the gapless edge states (due to the weak topological nature of the pairing) are defining properties of the nodeless dx2−y2*-wave pairing to be measured in future experiments.

Source-reported materials — not catalogue approval

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