Superconductivity by alloying the topological insulator SnBi2Te4

Abstract

Alloying indium into the topological insulator ${\mathrm{SnBi}}_{2}{\mathrm{Te}}_{4}$ induces bulk superconductivity with critical temperatures ${T}_{c}$ up to 1.85 K and upper critical fields up to about 14 kOe. This is confirmed by electrical resistivity, heat capacity, and magnetic susceptibility measurements. The heat capacity shows a discontinuity at ${T}_{c}$ and temperature dependence below ${T}_{c}$ consistent with weak coupling BCS theory, and suggests a superconducting gap near 0.25 meV. The superconductivity is type-II and the topological surface states have been verified by photoemission. A simple picture suggests analogies with the isostructural magnetic topological insulator ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$, in which a natural heterostructure hosts complementary properties on different sublattices, and motivates new interest in this large family of compounds. The existence of both topological surface states and superconductivity in ${\mathrm{Sn}}_{1\ensuremath{-}\mathrm{x}}{\mathrm{In}}_{\mathrm{x}}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ identifies these materials as promising candidates for the study of topological superconductivity.