Temperature Dependence of Spin and Bond Ordering in a Spin-Peierls System

TL;DR

This study uses quantum Monte Carlo simulations to analyze how temperature influences spin and lattice dimerization in a one-dimensional spin-Peierls system, revealing the transition process and effects of impurities.

Contribution

It provides a detailed temperature-dependent analysis of spin and bond ordering in a spin-Peierls system, including impurity effects, using a quantum Monte Carlo approach.

Findings

Dimerization increases as temperature decreases, reaching the ground state value.

High-temperature fluctuations cause deviations from uniform chain behavior.

Impurities induce edge localization of strong bonds and enhance magnetic order.

Abstract

We investigate thermodynamic properties of a one-dimensional S=1/2 antiferromagnetic Heisenberg model coupled to a lattice distortion by a quantum Monte Carlo method. In particular we study how spin and lattice dimerize as a function of the temperature, which gives a fundamental process of the spin-Peierls transition in higher dimensions. The degree of freedom of the lattice is taken into account adiabatically and the thermal distribution of the lattice distortion is obtained by the thermal bath algorithm. We find that the dimerization develops as the temperature decreases and it converges to the value of the dimerization of the ground state at T=0. Furthermore we find that the coupling constants of spins fluctuate quite largly at high temperature and there thermodynamic properties deviate from those of the uniform chain. Doping of non-magnetic impurities causes cut of the chain into short chains with open boundary. We investigate thermodynamic properties of open chains taking relaxation of the lattice into consideration. We find that strong bonds locate at the edges and a defect of the bond alternation appears in the chain with odd number of sites, which causes enhancement of the staggered magnetic order. We find a spreaded staggered structure which indicates that the defect moves diffusively in the chain even at very low temperature.