Electronic structure and superconductivity of the non-centrosymmetric Sn4As3

In a superconductor that lacks inversion symmetry, the spatial part of the Cooper pair wave function has a reduced symmetry, allowing for the mixing of spin-singlet and spin-triplet Cooper pairing channels and thus providing a pathway to a non-trivial superconducting state. Materials with a non-centrosymmetric crystal structure and with strong spin–orbit coupling are a platform to realize these possibilities. Here, we report the synthesis and characterisation of high quality crystals of Sn _4 As _3 , with non-centrosymmetric unit cell ( R 3 m ). We have characterised the normal and superconducting states using a range of methods. Angle-resolved photoemission spectroscopy shows a multiband Fermi surface and the presence of two surface states, confirmed by density-functional theory calculations. Specific heat measurements reveal a superconducting critical temperature of T _c ∼ 1.14 K and an upper critical magnetic field of μ _0 H _c ≳ 7 mT, which are both confirmed by ultra-low temperature scanning tunneling microscopy and spectroscopy. Scanning tunneling spectroscopy shows a fully formed superconducting gap, consistent with conventional s -wave superconductivity.