Topological phase transition under pressure in the topological nodal-line superconductor PbTaSe2

A first-order-like resistivity hysteresis is induced by a subtle structural transition under hydrostatic pressure in the topological nodal-line superconductor ${\mathrm{PbTaSe}}₂$. This structure transition is quickly suppressed to zero at pressure $\ensuremath{\sim}0.25$ GPa. As a result, superconductivity shows a marked suppression, accompanied with pronounced changes in the magnetoresistance and Hall resistivity. The first-principles calculations show that the spin-orbit interactions partially gap out the Dirac nodal line around $K$ point in the bulk Brillouin zone upon applying a small pressure, whereas the Dirac states around $H$ point are completely destroyed. The calculations further reveal a second structural phase transition under a pressure as high as $\ensuremath{\sim}30$ GPa, through which a transition from a topologically nontrivial bulk phase to a trivial phase is uncovered, with a superconducting dome emerging under this high-pressure phase. Our calculations also reveal how the bulk Fermi surfaces and the surface bands evolve with pressure. This theoretical study shall inspire in-depth experimental investigations on the electronic structure of this novel topological superconductor under higher pressures.