Semi-metallicity and electron-hole liquid in two-dimensional C and BN based compounds

TL;DR

This paper predicts a transition from insulator to metal in 2D carbon-based structures through substitutional atoms, revealing semi-metallic compounds with potential for excitonic insulator formation.

Contribution

It introduces a new class of 2D materials with tunable electronic properties via substitution, combining theoretical predictions and stability analysis.

Findings

Substitution of Si induces metallicity without band gap opening.

BN substitution maintains metallic properties in the structures.

The semi-metallic compounds are dynamically stable and suitable for excitonic insulator formation.

Abstract

Insulating-metallic transition mediated by substitutional atoms is predicted in a series of two-dimensional carbon-based structures. Introducing Si atoms in selected sites of tetrahexcarbon [Carbon 137 (2018) 266] according to rational chemical rules, metallicity by trivial band inversion without band gap opening is induced. Additional substitution of remaining C atoms by BN dimers introduces no changes in the metallic properties. A series of isomorphous two-dimensional materials with isoelectronic structures derived by exchanging group IV elements exhibiting various band gaps is obtained. Dynamical stability is verified with phonon analysis and beyond the harmonic approximation with molecular dynamics up to room temperature. The semi-metallic compounds have well-nested pockets of carriers and are good candidates for the formation of an excitonic insulator.