Superconducting and normal-state anisotropy of the doped topological insulator Sr${}_{0.1}$Bi${}_2$Se${}_3$

Abstract

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 $E_u$ symmetry in Sr${}_x$Bi${}_2$Se${}_3$.

arXiv comment10 pages, 7 figures, 3 supplemental pages

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