SPIN 1/2 XY MODEL .3. ANALYSIS OF HIGH-TEMPERATURE SERIES EXPANSIONS OF SOME THERMODYNAMIC QUANTITIES IN 2 DIMENSIONS

Analyses are reported of high temperature series expansions for the spin one-half XY model on the triangular and square lattices. Quantities for which series are analyzed include the fluctuation in the transverse magnetization, fourth order fluctuations in the same quantity, second and fourth moments of the transverse spin-spin correlations, specific heat, and entropy. The evidence favors a phase transition at a finite temperature with conventional power law critical singularities. Scaling seems to hold but hyperscaling seems to be violated. Estimates are given for critical exponents. The specific heat exhibits no singular behavior at T//c.