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Spin correlation functions and susceptibilities in the easy-plane XXZ chain

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

We present a Green's-function theory of magnetic short-range order in the $S=1/2$ easy-plane XXZ chain based on the projection method for the dynamic spin susceptibility and a decoupling of three-spin operator products introducing vertex parameters. The longitudinal and transverse static susceptibilities and two-point correlation functions of arbitrary range are calculated self-consistently for all wavenumbers, temperatures, and anisotropy parameters $ -1\leq Δ\leq 1$. In the easy-plane ferromagnetic region $(Δ< 0)$, the longitudinal correlators of spins at distance $n$ change sign at a finite temperature $T_0(n,Δ)$, in reasonable agreement with recent data obtained by finite-chain diagonalizations. The temperature dependence of the uniform static susceptibilities exhibits a maximum which is explained as an effect of magnetic short-range order which decreases with increasing temperature.

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C. Schindelin, H. Fehske, H. Büttner, D. Ihle. 2000-06-19. Spin correlation functions and susceptibilities in the easy-plane XXZ chain. https://doi.org/10.1103/physrevb.62.12141

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