Valence-bond solid to antiferromagnet transition in the two-dimensional Su-Schrieffer-Heeger model by Langevin dynamics

The two-dimensional Su-Schrieffer-Heeger model of electrons coupled to quantum phonons is investigated using Langevin dynamics within the framework of auxiliary-field quantum Monte Carlo. Based on an explicit determination of the density of zeros of the fermion determinant, it is argued that the method is efficient in the challenging adiabatic limit. Large-scale simulations at the O(4)-symmetric point establish that the ground state of the 2D SSH model undergoes a transition from a (pi, pi) valence bond solid to an antiferromagnet with increasing phonon frequency, yet still in the adiabatic regime. The single-particle spectrum illustrates the renormalization of the electronic band and suggests the existence of a gapped polaronic band, whereas the particle-hole channels show gapless modes associated with long-range bond and magnetic order, respectively. The simulations are supplemented with a mean-field analysis and a self-consistent Born approximation.

Automated summary

The two-dimensional Su-Schrieffer-Heeger model with electron-phonon coupling is investigated using Langevin dynamics and auxiliary-field quantum Monte Carlo. The efficient method in the challenging adiabatic limit is argued based on an explicit determination of the density of zeros of the fermion determinant. Large-scale simulations establish a transition from a (pi, pi) valence bond solid to an antiferromagnet as the phonon frequency increases. The single-particle spectrum shows renormalization and suggests the presence of a gapped polaronic band, while the particle-hole channels show gapless modes associated with long-range bond and magnetic order.