Pressure-induced superconductivity and structural transitions in topological insulator SnBi2Te4

The materials with topological phases have been a flexible platform for the realization of novel types of quantum matter due to their unique topology protected electron states. Herein, we report a comprehensive structural and electrical transport investigations on a topological insulator, SnBi 2 Te 4 , under high pressures by using diamond anvil cell techniques. Through in situ high pressure synchrotron x-ray diffraction studies, two structural phase transformations have been revealed. The powdered samples of SnBi 2 Te 4 transform from the initial layered quasi-two-dimensional structure (phase I) to a monoclinic C2/m structure (phase II) at about 7.14 GPa, and eventually develop into a site-disordered body centered cubic structure (phase III) at pressures above 18.9 GPa. Modifications of the electronic band structure have been discovered by the in situ high-pressure electrical measurements at low temperatures. It is noteworthy that three distinct pressure induced superconducting states have been observed, one in phase II and two in phase III. In each of the pressure induced superconducting states, the critical temperature Tc decreases with pressure. The maximum value of Tc is obtained in the third superconducting state emerging at the highest pressure range, which is 8.9 K at 22.3 GPa. A deep understanding of the relationship between the pressure induced structure-dependent superconducting states and the ambient-pressure topologically insulating state of SnBi 2 Te 4 may shed light on the universal physical nature that creates topologically insulating or superconducting states.