Pressure-induced superconductivity in weak topological insulator BiSe

TL;DR

This study demonstrates that pressure induces superconductivity in the topologically non-trivial layered material BiSe, with structural phase transitions and strong spin-orbit coupling effects contributing to its potential as a 3D topological superconductor.

Contribution

It provides the first experimental evidence of pressure-induced superconductivity in BiSe and links structural transitions, spin-orbit coupling, and topological surface states to its superconducting properties.

Findings

Superconductivity appears at ~8K under pressure.

Structural transitions occur at 8 GPa and 13 GPa.

Spin-orbit coupling influences topological and superconducting properties.

Abstract

Quasi-two-dimensional layered BiSe, a natural super-lattice with Bi2Se3-Bi2-Bi2Se3 units, has recently been predicted to be a dual topological insulator, simultaneously weak topological insulator as well as topological crystalline insulator. Here using structural, transport, spectroscopic measurements and density functional theory calculations, we show that BiSe exhibits rich phase diagram with the emergence of superconductivity with Tc ~8K under pressure. Sequential structural transitions into SnSe-type energetically tangled orthorhombic and CsCl-type cubic structures having distinct superconducting properties are identified at 8 GPa and 13 GPa respectively. Our observation of weak-antilocalization in magneto-conductivity suggests that spin-orbit coupling (SOC) plays a significant role in retaining non-trivial band topology in the trigonal phase with possible realization of 2D topological superconductivity. Theoretical analysis reveals that SOC significantly enhances superconducting Tc of the high-pressure cubic phase through an increase in electron-phonon coupling strength. Simultaneous emergence of Dirac-like surface states suggests cubic BiSe as a suitable candidate for the 3D-topological superconductor.