Superconductivity by Sr intercalation in the layered topological insulatorBi2Se3

Abstract

Strontium intercalation between van der Waals bonded layers of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is found to induce superconductivity with a maximum ${T}_{c}$ of 2.9 K. Transport measurement on a single crystal of the optimally doped sample ${\mathrm{Sr}}_{0.1}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ shows weak anisotropy $(\mathrm{\ensuremath{\Gamma}}\ensuremath{\sim}1.5)$ and an upper critical field ${H}_{c2}(0)$ equal to 2.1 T for a magnetic field applied perpendicular to the $c$ axis of the sample. The Ginzburg-Landau coherence lengths are found to be ${\ensuremath{\xi}}_{ab}=15.3$ nm and ${\ensuremath{\xi}}_{c}=10.2$ nm. The lower critical field ${H}_{c1,ab}(0)$ and zero temperature penetration depth ${\ensuremath{\lambda}}_{ab}(0)$ are estimated to be $0.39\ifmmode\pm\else\textpm\fi{}0.02$ mT and $1221\ifmmode\pm\else\textpm\fi{}36$ nm, respectively. Hall and Seebeck measurements confirm the dominance of electronic conduction, and the carrier concentration is surprisingly low $(n=1.85\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3})$ at 10 K, indicating the possibility of unconventional superconductivity.