Evidence for Fully Gapped Strong Coupling S-wave Superconductivity in Bi4O4S3

TL;DR

This study demonstrates that Bi4O4S3 is a fully gapped, strong-coupling s-wave superconductor with a higher-than-BCS energy gap ratio, confirmed through magnetic penetration depth measurements.

Contribution

It provides experimental evidence of fully gapped s-wave superconductivity in Bi4O4S3 with a notably high energy gap ratio, indicating strong coupling.

Findings

Bi4O4S3 exhibits conventional s-wave superconductivity.

The energy gap ratio 2Δ0/kBTc is 7.2, higher than BCS value.

Superfluid density fits a single-gap s-wave model.

Abstract

We report on the superconducting gap and pairing symmetry in layered superconductor Bi4O4S3. The measurement of temperature dependence of magnetic penetration depth was carried out using tunnel diode oscillator technique. It is observed that Bi4O4S3 is a conventional s-wave type superconductor with fully developed gap. The zero-temperature value of the superconducting energy gap {\Delta}0 was found to be 1.54 meV, corresponding to the ratio 2{\Delta}0/kBTc=7.2 which is much higher than the BCS value of 3.53. In the superconducting range, superfluid density is very well described by single gap s- wave model.