Possible unconventional pairing in \((\text{Ca,Sr})_{3}(\text{Ir,Rh})_{4}\text{Sn}_{13}\) superconductors revealed by controlling disorder

• Published in: arXiv.org
• Main Authors: Krenkel, E H, Tanatar, M A, Konczykowski, M, Grasset, R, Timmons, E I, Ghimire, S, Joshi, K R, Lee, Y, Ke, Liqin, Chen, S, Petrovic, C, Orth, P P, Scheurer, M S, Prozorov, R
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 26.02.2022
• Subjects: Charge density waves; Composition; Electron irradiation; Fermi surfaces; Fluids; Order parameters; Penetration depth; Physics - Superconductivity; Stannides; Strontium; Superconductivity; Superconductors; Superfluidity; Temperature dependence; Transition temperature
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2110.02025

We study the evolution of temperature-dependent resistivity with controlled point-like disorder induced by 2.5 MeV electron irradiation in stoichiometric compositions of the "3-4-13" stannides, \((\text{Ca,Sr})_{3}(\text{Ir,Rh})_{4}\text{Sn}_{13}\).Three of these cubic compounds exhibit a microscopic coexistence of charge-density wave (CDW) order and superconductivity (SC), while \(\text{Ca}_{3}\text{Rh}_{4}\text{Sn}_{13}\) does not develop CDW order. As expected, the CDW transition temperature, \(T_{\text{CDW}}\), is universally suppressed by irradiation in all three compositions. The superconducting transition temperature, \(T_{c}\), behaves in a more complex manner. In \(\text{Sr}_{3}\text{Rh}_{4}\text{Sn}_{13}\), it increases initially in a way consistent with a direct competition of CDW and SC, but quickly saturates at higher irradiation doses. In the other three compounds, \(T_{c}\) is monotonically suppressed by irradiation. The strongest suppression is found in \(\text{Ca}_{3}\text{Rh}_{4}\text{Sn}_{13}\), which does not have CDW order. We further examine this composition by measuring the London penetration depth, \(\lambda(T)\), from which we derive the superfluid density. The result unambiguously points to a weak-coupling, full single gap, isotropic superconducting state. Therefore, we must explain two seemingly incompatible experimental observations: a single isotropic superconducting gap and a significant suppression of \(T_{c}\) by non-magnetic disorder. We conduct a quantitative theoretical analysis based on a generalized Anderson theorem which points to an unconventional multiband \(s^{+-}\)-pairing state where the sign of the order parameter is different on one (or a small subset) of the smaller Fermi surface sheets, but remains overall fully-gapped.