Dynamical Plane Rotator Model. II. Dynamical Correlation Functions in Molecular Field Approximation

Abstract

Dynamical correlation functions S(q, ω)’s are obtained by the use of molecular field approximation for the dynamical plane rotator model:
(Remark: Graphics omitted.).
Our results are exact in the limit of long range interaction where J_ij is always J⁄N and in the limit of infinite N. Below the critical point T_c, S(q, ω)’s have two peaks corresponding to phonon excitation and sometimes a central peak at ω=0. Above T_c, however, they have only a central peak at ω=0. At T=T_c—, phenomena of critical slowing down are observed.