Correlation-Driven Dimerization and Topological Gap Opening in Isotropically Strained Graphene

TL;DR

This study uses advanced quantum Monte Carlo methods to reveal that isotropically strained graphene undergoes a correlation-driven dimerization transition, leading to a topological insulating state with a significant energy gap.

Contribution

It introduces an accurate off-lattice QMC approach to predict the phase diagram of strained graphene, highlighting a correlation-driven topological insulator phase.

Findings

Dimerized insulating state stabilizes between 8.5% and 15% strain.

The topological gap exceeds 1 eV before graphene's mechanical failure.

The dimerized phase is more stable than the antiferromagnetic state predicted by DFT.

Abstract

The phase diagram of isotropically expanded graphene cannot be correctly predicted by ignoring either electron correlations, or mobile carbons, or the effect of applied stress, as was done so far. We calculate the ground state enthalpy (not just energy) of strained graphene by an accurate off-lattice Quantum Monte Carlo (QMC) correlated ansatz of great variational flexibility. Following undistorted semimetallic graphene (SEM) at low strain, multi-determinant Heitler-London correlations stabilize between $\simeq$8.5% and $\simeq$15% strain an insulating Kekule-like dimerized (DIM) state. Closer to a crystallized resonating-valence bond than to a Peierls state, the DIM state prevails over the competing antiferromagnetic insulating (AFI) state favored by density-functional calculations which we conduct in parallel. The DIM stressed graphene insulator, whose gap is predicted to grow in excess of 1 eV before failure near 15% strain, is topological in nature, implying under certain conditions 1D metallic interface states lying in the bulk energy gap.