Quantum-classical crossover in the spin 1/2 XXZ chain
نویسندگان
چکیده
We compute, by means of exact diagonalization of systems of N = 16 and 18 spins, the correlation function < σz 0σ z n > at nonzero temperature for the XXZ model with anisotropy ∆. In the gapless ferromagnetic region −1 < ∆ < 0 for fixed separation the temperature can always be made sufficiently low so that the correlation is always negative. However we find that for sufficiently large temperatures and fixed separation or for fixed temperature 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. PACS 75.10.Jm, 75.40.Gb Typeset using REVTEX e-mail [email protected] e-mail [email protected]
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