# Robust and Pristine Top ological Dirac Semimetal Phase in Pressured Two-Dimensional Black Phosphorous

## TL;DR

This study demonstrates that applying hydrostatic pressure to phosphorene can induce a pristine two-dimensional topological Dirac semimetal phase with symmetry-protected Dirac cones, offering a feasible experimental pathway for topological phase transition.

## Contribution

The paper reveals that hydrostatic pressure, unlike electric fields or doping, can reliably induce a pristine 2D TDSM phase in phosphorene, clarifying the underlying mechanism.

## Key findings

- Hydrostatic pressure activates topological phase transition in phosphorene.
- The resulting TDSM state has a single pair of symmetry-protected Dirac cones.
- Dirac points are robust under external perturbations if glide-plane symmetry is preserved.

## Abstract

Very recently, in spite of various efforts in searching for two dimensional topological Dirac semimetals (2D TDSMs) in phosphorene, there remains a lack of experimentally efficient way to activate such phase transition and the underlying mechanism for the topological phase acquisition is still controversial. Here, from first-principles calculations in combination with a band-sorting technique based on k.p theory, a layer-pressure topological phase diagram is obtained and some of the controversies are clarified. We demonstrate that, compared with tuning by external electric-fields, strain or doping by adsorption, hydrostatic pressure can be an experimentally more feasible way to activate the topological phase transition for 2D TDSM acquisition in phosphorene. More importantly, the resultant TDSM state is a pristine phase possessing a single pair of symmetry-protected Dirac cones right at the Fermi level, in startling contrast to the pressured bulk black phosphorous where only a carrier-mixed Dirac state can be obtained. We corroborate that the Dirac points are robust under external perturbation as long as the glide-plane symmetry preserves. Our findings provide a means to realize 2D pristine TDSM in a more achievable manner, which could be crucial in the realization of controllable TDSM states in phosphorene and related 2D materials.