Unusual phase transition of layer-stacked borophene under pressure

TL;DR

This study reveals that layered borophene undergoes an unusual semimetal-semimetal phase transition under pressure, transforming into a fused 3D structure that retains Dirac fermion characteristics, contrasting with typical graphite-to-diamond transitions.

Contribution

It demonstrates a novel pressure-induced phase transition in borophene that preserves Dirac dispersion, supported by first-principles calculations and a simplified tight-binding model.

Findings

Fused borophene retains Dirac band dispersion

Pressure causes bond-breaking and reforming in borophene

Transition differs from graphite-to-diamond transformation

Abstract

The 8-Pmmn borophene, a boron analogue of graphene, hosts tilted and anisotropic massless Dirac fermion quasiparticles owing to the presence of the distorted graphene-like sublattice. First-principles calculations show that the stacked 8-Pmmn borophene is transformed into the fused three-dimensional borophene under pressure, being accompanied by the partially bond-breaking and bond-reforming. Strikingly, the fused 8-Pmmn borophene inherits the Dirac band dispersion resulting in an unusual semimetal-semimetal transition. A simple tight-binding model derived from graphene qualitatively reveals the underlying physics due to the maximum preservation of graphene-like substructure after the phase transition, which contrasts greatly to the transformation of graphite into diamond associated with the semimetal-insulator transition.