Thermodynamic properties of the two-dimensional spin-1/2 Heisenberg antiferromagnet at finite temperature: A finite-cluster-expansion approach

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Abstract
We have calculated the series for the internal energy and the specific heat of a two-dimensional spin-1/2 Heisenberg antiferromagnet at finite temperature on a square lattice using a finite-cluster-expansion method. The series are analyzed using a variant of Padé approximants. Our analysis agrees very well with the Monte Carlo simulation result for the internal energy per spin at T>0.3J and the specific heat at T>0.4J.