Topological linkage for thermoelectricity and superconductivity in their nontrivial topological state

Most thermoelectric materials and topological insulators were made from heavy elements and have narrow band gaps and strong spin-orbit couplings. The nontrivial topological insulating states are the essential base for the topological superconductivity. It remains unclear how the thermoelectric figure of merit performs in the topological state, and whether a thermoelectric material can evolve into a topological superconductor and what is the driving force if the latter happens. By choosing an n-type Bi₂Te_2.7Se_0.3, a highly efficient thermoelectric material and topological insulator, we perform measurements of the thermoelectric and superconducting properties at high pressures. We find that the figure of merit increases with pressure and exhibits a maximum at around 1 GPa where the topological phase transition takes place. After that, superconductivity appears and the critical temperature dramatically increases with increasing pressure in the phase with the nontrivial topological state. Its upper critical field exhibits different temperature dependence compared to the other superconducting phases without topological order. The topological phase transition is proposed to serve the linkage for the high-performance thermoelectricity and topological superconductivity.