Superconducting and normal-state anisotropy of the doped topological insulator Sr(0.1)Bi(2)Se(3)

Sr(x)Bi(2)Se(3) and the related compounds Cu(x)Bi(2)Se(3) and Nb(x)Bi(2)Se(3) have attracted considerable interest, as these materials may be realizations of unconventional topological superconductors. Superconductivity with T(c) ~3 K in Sr(x)Bi(2)Se(3) arises upon intercalation of Sr into the layered topological insulator Bi(2)Se(3). Here we elucidate the anisotropy of the normal and superconducting state of Sr(0.1)Bi(2)Se(3) with angular dependent magnetotransport and thermodynamic measurements. High resolution x-ray diffraction studies underline the high crystalline quality of the samples. We demonstrate that the normal state electronic and magnetic properties of Sr(0.1)Bi(2)Se(3) are isotropic in the basal plane while we observe a large two-fold in-plane anisotropy of the upper critical field in the superconducting state. Our results support the recently proposed odd-parity nematic state characterized by a nodal gap of Eu symmetry in Sr(x)Bi(2)Se(3).