Superconductivity in Tl_0.6Bi₂Te₃ Derived from a Topological Insulator

Bulk superconductivity has been discovered in Tl_0.6Bi₂Te₃, which is derived from the topological insulator Bi₂Te₃. A superconducting volume fraction of up to 95% (determined from the specific heat) with a T_c of 2.28 K was observed. The carriers are p-type with a density of ∼1.8 × 10²⁰ 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 that of 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 for a topological superconductor that may be realized by the strong spin-orbit coupling inherent to topological insulators.