PAI-graphene: a new topological semimetallic two-dimensional carbon allotrope with highly tunable anisotropic Dirac cones

TL;DR

This paper introduces PAI-graphene, a new 2D carbon allotrope with topologically protected Dirac cones, tunable electronic properties under strain, and potential for strain-controlled topological phase transitions.

Contribution

The study predicts a stable 2D carbon structure with nontrivial topology, demonstrating strain-tunable Dirac cones and topological phase transitions, expanding the understanding of topological materials.

Findings

PAI-graphene is a stable 2D carbon allotrope with lower energy than many known forms.

It hosts two Dirac cones at the Fermi level with high Fermi velocities.

Strain can modify Dirac cone positions and induce topological phase transitions.

Abstract

Using evolutionary algorithm for crystal structure prediction, we present a new stable two-dimensional (2D) carbon allotrope composed of polymerized as-indacenes (PAI) in a zigzag pattern, namely PAI-graphene whose energy is lower than most of the reported 2D allotropes of graphene. Crucially, the crystal structure realizes a nonsymmorphic layer group that enforces a nontrivial global topology of the band structure with two Dirac cones lying perfectly at the Fermi level. The absence of electron/hole pockets makes PAI-graphene a pristine crystalline topological semimetal having anisotropic Fermi velocities with a high value of $7.0 \times 10^{5}$ m/s. We show that while the semimetallic property of the allotrope is robust against the application of strain, the positions of the Dirac cone and the Fermi velocities can be modified significantly with strain. Moreover, by combining strain along both the x- and y-directions, two band inversions take place at $\Gamma$ leading to the annihilation of the Dirac nodes demonstrating the possibility of strain-controlled conversion of a topological semimetal into a semiconductor. Finally we formulate the bulk-boundary correspondence of the topological nodal phase in the form of a generalized Zak-phase argument finding a perfect agreement with the topological edge states computed for different edge-terminations.