MONTE-CARLO STUDY OF CHIRAL CRITICALITY - XY AND HEISENBERG STACKED-TRIANGULAR ANTIFERROMAGNETS

The results of extensive Monte Carlo simulations are reported on XY and Heisenberg antiferromagnets on a d = 3-dimensional stacked-triangular lattice, which are expected to belong to the recently identified n = 2 and 3 chiral universality classes, respectively. The lattices studied consist of L3 spins with 18 less-than-or-equal-to L less-than-or-equal-to 60. The study is an extension of earlier Monte Carlo simulations for the same system with smaller lattices. A continuous transition characterized by the novel critical exponents is found with alpha = 0.34 +/- 0.06, beta = 0.253 +/- 0.01, gamma = 1.13 +/- 0.05 and nu = 0.54 +/- 0.02 for the XY (n = 2) case, and with alpha = 0.24 +/- 0.08, beta = 0.30 +/- 0.02, gamma = 1.17 +/- 0.07 and nu = 0.59 +/- 0.02 for the Heisenberg (n = 3) case. The specific-heat amplitude ratio is estimated to be A+/A- = 0.36 +/- 0.2 and A+/A- = 0.54 +/- 0.2 in the n = 2 and n = 3 cases, respectively. The nature of the chiral ordering is also studied, and various chirality exponents are determined. The results are discussed in conjunction with the recent renormalization-group calculations and experiments.