Neel to spin-Peierls transition in the ground state of a quasi-1D Heisenberg model coupled to bond phonons

TL;DR

This study investigates the spin-Peierls transition in a quasi-1D Heisenberg model with bond phonons using quantum Monte Carlo, revealing a finite critical spin-lattice coupling for dimerization and mapping the phase diagram.

Contribution

It demonstrates that finite inter-chain coupling requires a non-zero critical spin-lattice coupling for the transition, contrasting with the pure 1D case, and maps the phase diagram of the system.

Findings

Transition occurs only above a critical coupling value.

No coexistence of magnetic order and dimerization.

Neel order vanishes with the onset of dimerization.

Abstract

The spin-Peierls transition in the ground state of a quasi-one-dimensional spin-1/2 Heisenberg model coupled to adiabatic bond phonons is studied using a quantum Monte Carlo (QMC) method. The transition from a gapless Neel state to a spin-gapped Peierls state is explored in the parameter space spanned by the spatial anisotropy and the strength of spin-lattice coupling. It is found that for any finite inter-chain coupling, the transition to a dimerized Peierls ground state occurs only when the spin-lattice coupling exceeds a finite, non-zero critical value. This is in contrast to the pure 1D model, where adiabatic phonons lead to a dimerized ground state for any non-zero spin-phonon coupling. The phase diagram in the above parameter space is mapped out. No evidence is found for a region of co-existing long range magnetic order and dimerization. The vanishing of the Neel order occurs simultaneously with the setting in of the dimerization.