Pressure-induced superconductivity in the weak topological insulator BiSe
Pallavi Malavi, Arpita Paul, Achintya Bera, D. V. S. Muthu, Kunjalata Majhi, Pankaj Kumar, Umesh V. Waghmare, A. K. Sood, S. Karmakar
Abstract
Layered BiSe in the trigonal $P\overline{3}m1$ phase is a weak topological insulator and a candidate topological crystalline insulator. Here using structural, spectroscopic, resistance measurements at high pressure and density functional theory calculations, we report that BiSe exhibits a rich phase diagram with the emergence of superconductivity above 7 GPa. Structural transitions into SnSe-type energetically tangled orthorhombic structures and, subsequently, into a CsCl-type cubic structure having distinct superconducting properties are identified at 8 and 13 GPa, respectively. Superconductivity is preserved as the system transforms back to the trigonal phase upon release of pressure. Spin-orbit coupling plays a significant role in enhancement of ${T}_{c}$ in the trigonal and cubic phases. In the orthorhombic $Cmcm$ phase, ${T}_{c}$ decreases monotonically with increasing pressure, whereas unusual pressure-independent ${T}_{c}$ is observed in the cubic $Pm\overline{3}m$ phase. Theoretical analysis reveals topological surface states in the cubic phase. The emergence of superconductivity within the topological phases makes BiSe a candidate topological superconductor.