Two-dimensional spin-1/2 Heisenberg antiferromagnet at finite temperature

We analyzed the high-temperature series of the two-dimensional spin-1/2 Heisenberg antiferromagnet using a variant of the Padé approximant method. Our analysis agrees very well with the Monte Carlo simulation result. Specifically, the agreement is very good for the internal energy per spin at T>0.3J, for the specific heat and for the uniform susceptibility at T>0.5J on a square lattice. We also analyzed the internal-energy series on a triangular lattice. The ground-state energy per spin at zero temperature is found to be ${\mathit{E}}_{\mathit{g}}$/N=-0.524, which is in good agreement with the values obtained by simulations and spin-wave theory.