Surface superconductivity and topological band in the strong-coupling superconductor SrSn3

Abstract

The system with the interplay between superconductivity, nontrivial band topology and strongly correlated electrons is of great interest due to the emergent novel quantum phases, such as topological superconductivity and strongly correlated topological phases. Such system is rarely found in realistic materials, recent examples are moiré graphene, FeTe0.55Se0.45 and kagome superconductors. In this work, we report that SrSn3 is a prototype of superconducting alloy with an odd Z2 invariant, which is supported by the existence of topologically nontrivial surface states. Moreover, we find that strong spin-orbit coupling plays a dominant role in the formation of the flat-bands at Fermi level in SrSn3, which result in both considerable electron correlations (identified by a large carrier effective mass mC*/m0≈3.06 and a large Kadowaki-Wood ratio A/γ2∼7.94×10−4µΩcmmJ2mol2K2) and strong-coupling superconductivity (2Δ/kBTc∼4.90 and Tc/TF∼2.34×10−3), that coexist with the topological surface states, characterized by the nontrivial Berry phase of de Hass-van Alphen oscillations (ϕB∼π). Remarkably, we observed a surface superconducting state, manifested as an extremely large surface-to-bulk critical field ratio (Hc3/Hc2∼18.3) and a linear temperature-dependent critical field. Our findings reveal that SrSn3 is a promising candidate for studying the interplay between nontrivial band topology and correlated electron phenomena induced by strong spin-orbit coupling.

Source-reported materials — not catalogue approval

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