Superconducting gap structure in ambient-pressure-grown $\mathrm{La}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}\mathrm{Bi}{\mathrm{S}}_2$

Abstract

We have performed transverse-field muon spin relaxation (TF-$\mu$SR) measurements on ambient-pressure-grown polycrystalline $\mathrm{La}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}\mathrm{Bi}{\mathrm{S}}_2$. From these measurements, no signature of magnetic order is found down to 25 mK. The value of the magnetic penetration depth extrapolated to 0 K is 0.89 (5) $\mu$m. The temperature dependence of superconducting penetration depth is best described by either a multigap s + s-wave model with ${\Delta }_1$ = 0.947 (7) meV and ${\Delta }_2$ = 0.22 (4) meV or the ansiotropic s-wave model with $\Delta (0)$ = 0.776 meV and anisotropic gap amplitude ratio ${\Delta }_{min}/{\Delta }_{max}$ = 0.34. Comparisons with other potentially multigap $\mathrm{Bi}{\mathrm{S}}_2$-based superconductors are discussed. We find that these $\mathrm{Bi}{\mathrm{S}}_2$-based superconductors, including $\mathrm{B}{\mathrm{i}}_4{\mathrm{O}}_4{\mathrm{S}}_3$ and the high-pressure synthesized $\mathrm{La}{\mathrm{O}}_{0.5}{\mathrm{F}}_{0.5}\mathrm{Bi}{\mathrm{S}}_2$, generally conform to the Uemura relation.

6 pages, 4 figures

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