Superconductivity in BiSbTeSe(= 1.0 and= 2.0) under pressure.

The crystal structure of BiSbTeSe(BiSbTeSe(= 1.0 and= 2.0)) at 0-29 GPa is investigated through synchrotron x-ray diffraction (XRD) and two structural phase transitions are discovered. The stoichiometry of BiSbTeSeemployed in this study is BiSbTeSe, as determined from energy-dispersive x-ray spectroscopy. The sample demonstrated structural transitions, from a rhombohedral structure (space group no 166,3¯) (phase I) to a monoclinic structure (space group no 12,2/) (phase II), and from phase II to a 9/10-fold monoclinic structure (space group no 12,2/) (phase III). The temperature dependence of resistance (-plot) exhibited a semiconducting behavior in a low pressure range and changed from semiconducting to metallic behavior with increasing pressure. Pressure-driven superconductivity is observed above 9.1 GPa in BiSbTeSe. The pressure phase corresponds to phase II. The superconducting transition temperature,, increased with pressure. The maximumvalue is 8.3 K at 19.1 GPa. The magnetic field dependence ofin phase II of BiSbTeSeis proceeded by a-wave polar model, indicating topologically nontrivial superconductivity. In addition, the emergence of superconductivity and the change in superconducting behavior are closely associated with the structural transitions.