FINITE TEMPERATURE NÉEL TRANSITION IN CPN−1 MODEL

Abstract

We study in d space-dimensions the finite temperature Néel order transition in CPN−1 model as a low energy effective field theory of the antiferromagnetic Heisenberg model. For d=1 at any temperature and d=2 at any nonzero temperature, long range Néel order (LRNO) disappears, in agreement with the Mermin-Wagner-Coleman theorem. For d=3 in the weak coupling region, LRNO exists below the critical temperature T N (Néel temperature). T N decreases as the interlayer coupling becomes relatively weak compared with that within Cu-O layers.