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Quantum to classical crossover in the 2D easy-plane XXZ model

H. Fehske·C. Schindelin·A. Weiße·H. Büttner·D. Ihle
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Abstract

Ground-state and thermodynamical properties of the spin-1/2 two-dimensional easy-plane XXZ model are investigated by both a Green's-function approach and by Lanczos diagonalizations on lattices with up to 36 sites. We calculate the spatial and temperature dependences of various spin correlation functions, as well as the wave-vector dependence of the spin susceptibility for all anisotropy parameters $Δ$. In the easy--plane ferromagnetic region $(-1< Δ< 0)$, the longitudinal correlators of spins at distance $r$ change sign at a finite temperature $T_0(Δ, {\bf r})$. This transition, observed in the 2D case for the first time, can be interpreted as a quantum to classical crossover.

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H. Fehske, C. Schindelin, A. Weiße, H. Büttner, D. Ihle. 2000-06-17. Quantum to classical crossover in the 2D easy-plane XXZ model. https://doi.org/10.1590/s0103-97332000000400015

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