Superconductivity by Sr intercalation in the layered topological insulator Bi2Se3

Strontium intercalation between van der Waals bonded layers of the topological insulator Bi2Se3 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 Sr0.1Bi2Se3 shows weak anisotropy (Gamma similar to 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 xi(ab) = 15.3 nm and xi(c) = 10.2 nm. The lower critical field H-c1,H-ab(0) and zero temperature penetration depth lambda(ab)(0) are estimated to be 0.39 +/- 0.02 mT and 1221 +/- 36 nm, respectively. Hall and Seebeck measurements confirm the dominance of electronic conduction, and the carrier concentration is surprisingly low (n = 1.85 x 10(19) cm(-3)) at 10 K, indicating the possibility of unconventional superconductivity.