Recently, a research team from the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences and Center for High Pressure Science and Technology Advanced Research carried out systematic research on the superconductivity and electron-phonon interaction in SrxBi₂Se₃ under high pressure. The related research results have been Accepted Manuscript online in New Journal of Physics on 15 July 2021.

Scientists of condensed matter physics focused on the pressure-induced topological superconductivity and underlying mechanism of Bi2Se3-based topological materials in recent years. Albeit the superconductivity has a close connection to the structural phase transitions, the electrons pairing mechanism of these semiconductor phase and high pressure phases remains an open question. The initial phase is actually close to or even violating the Born-Oppenheimer approximation due to the low carrier density, which results in the inappropriate description of the electrons pairing described by the standard BCS theory. Hence in this work, a comprehensive study of the pressure effect on the superconducting properties and lattice dynamics of SrxBi₂Se₃ single crystal, a topological superconductor candidate was presented. It was found that the origin of the reemergence of superconductivity of SrxBi₂Se₃ is due to electronic transition other than structural transition as reported previously.

Another key finding is the observation of a cooperative connection between the strength of electron-phonon interaction generated by the optical branches and the pressure-tunable superconductivity in rhombohedral SrxBi₂Se₃ crystal, which violates the adiabatic-limit. It is proposed that the suppression mechanism of by pressure is ascribed to the weakening of the interaction of electrons with optical phonon modes for the rhombohedral phase. During the adjustment of pressure phases process, in the monoclinic phase, the sharp increase of value is observed accompanying with the accumulation of carrier density. This is intuitively unusual since it is expected the electron-phonon interaction shall be weakened by adding more conducting carriers in a normal metal.

In the tetragonal phase, since it is fully metallized and obeys the adiabatic Born-Oppenheimer approximation well, the superconductivity can be interpreted within BCS theory. These findings are important for fully understanding the unconventional superconductivity and pairing mechanism in the layered rhombohedral Bi2Se3-based superconductors.

This work is a cooperative study of inovation and integration center of new laser technology, Shanghai Institute of Optics and Fine Mechanics, with the Center for High Pressure Science and Technology Advanced Research, Yanshan University, Fudan University and Argonne National Laboratory, and is supported by the Natural Science Foundation of China and Shanghai Sailing Program.