Quantum-classical crossover in the spin 1/2 XXZ chain
Abstract
We compute, by means of exact diagonalization of systems of N=16 and 18 spins, the correlation function <\sigma^z_0\sigma^z_n> at nonzero temperature for the XXZ model with anisotropy \Delta. In the gapless ferromagnetic region -1<\Delta<0 for fixed separation the temperature can always be made sufficiently low so that the correlation is always negative for n \neq 0. However we find that for sufficiently large temperatures and fixed separation or for fixed temperature greater than some T0(\DElta) and sufficiently large separations the correlations are always positive. This sign changing effect has not been previously seen and we interpret it as a crossover from quantum to classical behavior.
Cite
@article{arxiv.cond-mat/9805337,
title = {Quantum-classical crossover in the spin 1/2 XXZ chain},
author = {Klaus Fabricius and Barry M. McCoy},
journal= {arXiv preprint arXiv:cond-mat/9805337},
year = {2009}
}
Comments
17 pages, 7 tables, 2 figures The value of T0(\Delta) at which the crossover occurs has been determined