Low superfluid density and possible multigap superconductivity in the BiS 2 -based layered superconductor Bi 4 O 4 S 3

Abstract

The magnetic penetration depth λ as a function of temperature in Bi4O4S3 was studied by muon-spin-spectroscopy measurements. The superfluid density of Bi4O4S3 is found to be very low. The dependence of λ-2 on temperature possibly suggests the existence of two s-wave-type energy gaps with the zero-temperature values of 0.93 (3) and 0.09 (4) meV. The upturn in the temperature dependence of the upper critical field close to Tc further supports multigap superconductivity in Bi4O4S3. The presence of two superconducting energy gaps is consistent with theoretical and other experimental studies. However, a single-gap s-wave model fit with a gap of 0.88 (2) meV cannot be ruled out completely. The value of λ(T) at T=0 K is estimated to be λ(0)=861(17) nm, one of the largest of all known layered superconductors, reflecting a very low superfluid density. © 2013 American Physical Society.