Correlation-Driven Kekule’ Dimerization and Semimetal-Insulator Transition in Strongly Isotropically Strained Graphene*

Freestanding graphene will spontaneously distort and become insulating under a large isotropic tensile strain. We calculate the ground state enthalpy (not just energy) of strongly strained graphene by an off-lattice quantum Monte Carlo correlated approach of great accuracy and variational flexibility, removing the limitations of earlier density-functional or rigid lattice approaches. Beginning with undistorted semimetallic graphene at low strain, we find [1] that multideterminant Heitler-London correlations stabilize between 8.5% and 15% tensile strain an insulating Kekule' dimerized state. Closer to a crystallized resonating-valence bond than to a Peierls state, Kekule’ dimerization of graphene prevails over the competing antiferromagnetic insulating state favored by density-functional calculations which we conduct in parallel. The insulator gap grows from zero at onset to over 1 eV before mechanical failure near 15% strain, and is topological in nature, implying under certain conditions 1D metallic interface states lying in the bulk energy gap. [1] S. Sorella, et al., PRL 121, 066402 (2018).