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Abstract

Weinvestigate thermodynamic properties like specific heat cV and susceptibility chi in anisotropic J(1)-J(2) triangular quantum spin systems (S = 1/2). As a universal tool we apply the finite temperature Lanczos method (FTLM) based on exact diagonalization of finite clusters with periodic boundary conditions. Weuse clusters up to N = 28 sites where the thermodynamic limit behavior is already stably reproduced. As a reference we also present the full diagonalization of a small eight-site cluster. After introducing model and method we discuss our main results on c(V)(T) and chi(T). We show the variation of peak position and peak height of these quantities as function of control parameter J(2)/J(1). We demonstrate that maximum peak positions and heights in Nuel phase and spiral phases are strongly asymmetric, much more than in the square lattice J(1)-J(2) model. Our results also suggest a tendency to a second side maximum or shoulder formation at lower temperature for certain ranges of the control parameter. Wefinally explicitly determine the exchange model of the prominent triangular magnets Cs2CuCl4 and Cs2CuBr4 from our FTLM results.