Superconducting phases of BiTe at high pressure

Quasi-two-dimensional (2D) layered structured BiTe, a member of the infinitely adaptive series ${({\mathrm{Bi}}_{2})}_{m}{({\mathrm{Bi}}_{2}{\mathrm{Te}}_{3})}_{n}$, is an efficient thermoelectric material and a dual topological insulator at ambient pressure. This undergoes pressure-induced sequential structural transitions into various 3D network structures (SnTe-type) and superconductivity emerges at elevated pressures. Here, using systematic high-pressure x-ray diffraction, Raman scattering, optical conductivity, and transport measurements, we identify the 2D and 3D BiTe phases with their distinct superconducting and normal state transport properties. Superconductivity emerges with ${T}_{c} \ensuremath{\sim}2\mathrm{K}$ at 3 GPa within the 2D layered phase, where evidence of enhanced spin polarization of the Rashba surface states are found. This superconductor (SC) phase has been unambiguously identified by its much lower ${T}_{c}$, critical field and critical current, as compared to the high-pressure 3D phases. With pressure the 3D BiTe phase evolves from orthorhombic phase into atom-disordered body-centered cubic alloy phase, where a dramatic increase of the electronic phase relaxation rate is noticed within the enhanced metallic character. The observed sharp resistance peak anomaly near SC ${T}_{c}$ in the high-pressure 3D crystalline BiTe phases are interpreted as novel metal--bosonic insulator--superconductor transitions and the possible origins of this phenomena are discussed based on the magnetoresistance measurements.