Superconductivity, valence skipping, and topological crystalline metallic phase in AgSnSe2

Abstract

The recent suggestion of valence-skipping phenomenon driving a two-gap superconductivity in Ag-doped SnSe by Kataria et al. [Phys. Rev. B 107, 174517 (2023)] has brought to the fore a long-standing issue once again. The absence of crystallographically inequivalent Sn sites corroborated by electronic properties of AgSnSe2, calculated using first-principles density functional theory, however, does not appear to provide strong support in favor of valence skipping in AgSnSe2. Interestingly, the signature of avoided band crossings (with the inclusion of spin-orbit coupling) and nonzero mirror Chern number (nM) suggest a nontrivial topology. The presence of mirror symmetry-protected surface states along the mirror planes indicates that AgSnSe2 could be a potential candidate for topological crystalline metals (TCMs), with a transition from a topological crystalline insulator phase to a TCM phase under Ag doping. Moreover, using the Migdal-Eliashberg theory of electron-phonon coupling and anisotropic superconductivity in AgSnSe2, we predict a single superconducting gap and a critical temperature Tc≈7K, consistent with the experimental value. The interplay of topology and superconductivity in this three-dimensional material appears quite intriguing and may provide insights into the nature of superconductivity in systems with nontrivial topology.

Source-reported materials — not catalogue approval

Similar papers