# Topological Phase Transition Under Pressure in the Topological Nodal Line Superconductor PbTaSe$_2$

## TL;DR

This study investigates how pressure induces topological and structural phase transitions in the superconductor PbTaSe$_2$, revealing a Lifshitz transition, partial gapping of Dirac nodal lines, and a high-pressure transition to a trivial phase with superconductivity.

## Contribution

It provides the first detailed analysis of pressure-induced topological and structural phase transitions in PbTaSe$_2$, combining experimental resistivity data with first principles calculations.

## Key findings

- Pressure induces a structural transition suppressed at ~0.25 GPa.
- A Lifshitz transition occurs around ~0.25 GPa affecting electronic properties.
- A high-pressure transition at ~30 GPa changes topological phase and induces superconductivity.

## Abstract

A first-order-like resistivity hysteresis is induced by a subtle structural transition under hydrostatic pressure in the topological nodal-line superconductor PbTaSe$_2$. This structure transition is quickly suppressed to zero at pressure $\sim$0.25 GPa. As a result, superconductivity shows a marked suppression, accompanied with fundamental changes in the magnetoresistance and Hall resistivity, suggesting a Lifshitz transition around $\sim$0.25 GPa. The first principles calculations show that the spin-orbit interactions partially gap out the Dirac nodal line around $K$ point in the Brillouin zone upon applying a small pressure, whilst the Dirac states around $H$ point are completely destroyed. The calculations further reveal a second structural phase transition under a pressure as high as $\sim$30 GPa, through which a transition from a topologically nontrivial phase to a trivial phase is uncovered, with a superconducting dome emerging under this high-pressure phase.