Abstract Body

Despite the large variety of different mineral compounds found in the earth's crust, most materials of interest in solid state physics are artificial, i.e. only produced in the lab. Apart from native metals such as tin or lead, naturally-occurring superconducting compounds are rare. One of only a handful of such materials is the cubic mineral Rh₁₇S₁₅, also known as miassite, which can be found near the Miass River in the southern Urals of Russia. Although the first observation of superconductivity in laboratory-grown RRh₁₇S₁₅ was reported almost 7 decades ago [1], this material has attracted renewed interest in the last 15 years as a strongly-correlated superconductor. In particular, both the heat capacity jump at the critical temperature and the upper critical field significantly exceed theoretical expectations [2]. Nevertheless, the key microscopic parameter governing the superconductivity – the superconducting gap – has remained unclear.

Here I will outline our work to determine this superconducting gap through penetration depth and controlled disorder experiments [3]. The consistent picture emerging from our results indicates that Rh₁₇S₁₅ has line nodes; our theoretical analysis suggests an extended s-wave gap in the A_1g irrep. This makes Rh₁₇S₁₅ the only example of a naturally-occurring unconventional superconductor.

References

[1]  B. T. Matthias, E. Corenzwit, and C. E. Miller, Phys. Rev. 93, 1415 (1954).
[2] H. R. Naren, A. Thamizhavel, A. K. Nigam, and S. Ramakrishnan, Phys. Rev. Lett. 100, 026404 (2008).
[3] H. Kim, M. A. Tanatar, M. Kończykowski, U. S. Kaluarachchi, S. Teknowijoyo, K. Cho, A. Sapkota, J. M. Wilde, M. J. Krogstad, S. L. Bud’ko, P. M. R. Brydon, P. C. Canfield, and R. Prozorov, arXiv:2306.00261