London, λL(T), and Campbell, λC(T), penetration depths were measured in single crystals of a topological superconductor candidate AuSn4. At low temperatures, λL(T) is exponentially attenuated and, if fitted with the power law, λ(T)∼Tn, gives exponents n>4, indistinguishable from the isotropic single s−wave gap Bardeen-Cooper-Schrieffer (BCS) asymptotic. The superfluid density fits perfectly in the entire temperature range to the BCS theory. The superconducting transition temperature, Tc=2.40±0.05K, does not change after 2.5 MeV electron irradiation, indicating the validity of the Anderson theorem for isotropic s−wave superconductors. Campbell penetration depth before and after electron irradiation shows no hysteresis between the zero-field cooling (ZFC) and field cooling (FC) protocols, consistent with the parabolic pinning potential. Interestingly, the critical current density estimated from the original Campbell theory decreases after irradiation, implying that a more sophisticated theory involving collective effects is needed to describe vortex pinning in this system. In general, our thermodynamic measurements strongly suggest that the bulk response of the AuSn4 crystals is fully consistent with the isotropic s−wave weak-coupling BCS superconductivity.
@article{arxiv.2407.03587,
title = {Single-gap Isotropic $s-$wave Superconductivity in Single Crystals $\text{AuSn}_4$},
author = {Sunil Ghimire and Kamal R. Joshi and Elizabeth H. Krenkel and Makariy A. Tanatar and Marcin Konczykowski and Romain Grasset and Paul C. Canfield and Ruslan Prozorov},
journal= {arXiv preprint arXiv:2407.03587},
year = {2024}
}