Pressure-induced superconductivity and topological phase transitions in the topological nodal-line semimetal SrAs₃

Topological nodal-line semimetals (TNLSMs) are materials whose conduction and valence bands cross each other, meeting a topologically-protected closed loop rather than discrete points in the Brillouin zone. TNLSMs have several anticipated properties, such as drumhead-like nearly flat surface states, the possibility of realizing high-temperature superconductivity and so on. Recently, SrAs₃ has been theoretically proposed and then experimentally confirmed to be a TNLSM. Here, we report high-pressure experiments on SrAs₃, identifying a Lifshitz transition below 1 GPa and a superconducting transition accompanied by a structural phase transition above 20 GPa. A topological crystalline insulator (TCI) state is revealed by means of density functional theory calculations on the emergent high-pressure phase. As the counterpart of topological insulators, TCIs possess metallic boundary states protected by crystal symmetry, rather than time reversal. In consideration of topological surface states and helical spin texture observed in the high-pressure state of SrAs₃, the superconducting state may be induced in the surface states, and is most likely topologically nontrivial, making pressurized SrAs₃ a strong candidate for topological superconductor.