Pressure-induced structural transitions, alloying and superconductivity in topological insulators Bi2Te2Se and Bi2Se2Te

Abstract

Over the past decade, external pressure has been found to play an important role in modulating the structures and properties of sesqui-chalcogenides, but several key puzzles still remain to be solved. In this work, pressure-induced structural phase transitions, alloying and topological superconductivity in the ternary tetradymites Bi₂Te₂Se and Bi₂Se₂Te were investigated via in situ high-pressure angle-dispersive X-ray diffraction and resistance measurements. Both of them transform from the layered rhombohedral Rm structure to a 7-fold monoclinic C2/m phase, then to an 8-fold monoclinic C2/c structure, and eventually to a bcc alloy, which are quite different from previous work, but similar to the transitions in Bi₂Te₃. The superconductivity was found in the rhombohedral structure of Bi₂Se₂Te with T_c ≈ 2.2 K at 4.3 GPa, which should be related to the topological quantum transition. Furthermore, the atomic size and element electronegativity were discovered to have a significant effect on the alloying and amorphization of these compounds.