High-temperature expansions of partition function for the spin- XY model

Donald D. Betts, C. J. Elliott, M. Howard Lee

Jos Rogiers, Raf Dekeyser

Jos Rogiers, Raf Dekeyser

M. Howard Lee

The high-temperature expansion of the spin-½ XY model is shown to be particularly simple when the Hamiltonian is written in the second-quantization form. By aid of a few simple rules, the partition function and susceptibility are easily evaluated to high orders.

P. Butera, M. Pernici

The high-temperature expansion of the spin-spin correlation function of the two-dimensional classical XY (planar rotator) model on the square lattice is extended by three terms, from order 21 through order 24, and analyzed to improve the estimates of the critical parameters.

P. Butera, M. Pernici

The high-temperature expansions for the spin-spin correlation function of the two-dimensional classical XY (planar rotator) model are extended by two terms, from order 24 through order 26, in the case of the square lattice, and by five terms, from order 15 through order 20, in the case of the triangular lattice. The data are analyzed to improve the current estimates of the critical parameters of the models.