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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.
