Superconductivity in Tl_(0.6)Bi₂Te₃ Derived from a Topological Insulator

Bulk superconductivity has been discovered in Tl_{0.6}Bi_{2}Te_{3}, which is derived from the topological insulator Bi2Te3. The superconducting volume fraction of up to 95% (determined from specific heat) with Tc of 2.28 K was observed. The carriers are p-type with the density of ~1.8 x 10^{20} cm^{-3}. Resistive transitions under magnetic fields point to an unconventional temperature dependence of the upper critical field B_{c2}. The crystal structure appears to be unchanged from Bi2Te3 with a shorter c-lattice parameter, which, together with the Rietveld analysis, suggests that Tl ions are incorporated but not intercalated. This material is an interesting candidate of a topological superconductor which may be realized by the strong spin-orbit coupling inherent to topological insulators.