Antiferromagnetic and Kekulé Valence Bond Solid Correlations in the Optical Su-Schrieffer-Heeger-Hubbard Model on a Honeycomb Lattice

This talk discusses results from numerically exact determinant quantum Monte Carlo simulations of the half-filled optical Su-Schrieffer-Heeger (oSSH)-Hubbard model on a honeycomb lattice. In this model two dispersionless optical phonon modes are placed on each orbital in the lattice. These phonon modes couple to the electrons via a Su-Schrieffer-Heeger-like electron-phonon (e-ph) coupling mechanism in which the phonon displacements linearly modulate the nearest-neighbor hopping amplitudes. Electronic correlations are then introduced via a local repulsive Hubbard interaction. Consistent with previous work, we find that the ground-state phase diagram includes competing Dirac semi-metal (SM), antiferromagnetic (AFM) and Kekulé valence bond solid (KVBS) phases. However, we also observe a region of AFM-KVBS coexistence, as well as a parameter regime in which, for fixed e-ph coupling strength, increasing the Hubbard interaction results in a SM to KVBS phase transition. Lastly, we discuss the significance of our results for graphene-based systems, and specifically the effect that applied mechanical strains have on emergent AFM and KVBS correlations.