Flux growth, mixed valence state and superconductivity of Sn4Sb3 intermetallic crystals

Single crystals of Sn4Sb3 with mm size have been obtained for the first time via a Sn flux method. Structural refinements confirm its trigonal structure with the centrosymmetric R3̄m space group. The unit cell consists of ordered [Sn–Sb–Sn–Sb–Sn–Sb–Sn] lamellae stacked along the c-axis, in which Sn is found to exhibit mixed valence states of 0 and 2+. Below 1.47 K, single crystalline Sn4Sb3 becomes a weakly coupled, fully gapped superconductor. In contrast to polycrystalline samples, the resistive transition of Sn4Sb3 crystals coincides well with the specific-heat jump, which supports that grain boundaries are responsible for the higher resistive Tc in the former case. Theoretical calculations show that the density of states at the Fermi level are mainly contributed by Sn and Sb 5p orbitals and almost unaffected by the spin-orbit interaction. Our study lays a foundation for experimental investigations of the predicted topological properties in this intermetallic compound.