The spin-Peierls instability in spin 1/2 XY chain in the non adiabatic limit

TL;DR

This paper investigates the spin-Peierls instability in a spin 1/2 XY chain coupled to phonons in the nonadiabatic limit, revealing phase transitions and order parameters through a variational and mean-field approach.

Contribution

It introduces a variational method using Lang-Firsov wave function to analyze the nonadiabatic spin-phonon coupling effects in the XY chain.

Findings

Identification of a dimerized phase below a critical coupling

Observation of an antiferromagnetic phase above the critical coupling

Analysis of lattice distortion and energy gap variations

Abstract

The spin-Peierls instability in spin 1/2 XY chain coupled to dispersionless phonons of frequency $\omega$ has been studied in the nonadiabatic limit. We have chosen the Lang-Firsov variational wave function for the phonon subsystem to obtain an effective spin Hamiltonian. The effective spin Hamiltonian is then solved in the framework of mean-field approximation. We observed a dimerized phase when g is less than a critical value and an anti-ferromagnetic phase when it is greater than a critical value . The variation of lattice distortion, dimerized order parameter and energy gap with spin phonon coupling parameter has also been investigated here.