The quantum easy-plane ferromagnetic two-dimensional XXZ model is approached by the pure-quantum self-consistent harmonic approximation that reduces it to an effective classical model. Quantum fluctuations weaken both the effective exchange, leading to a reduced Berezinskii-Kosterlitz-Thouless transition temperature with respect to the classical model, and the effective easy-plane anisotropy. The latter vanishes when the anisotropy is smaller than a cutoff value, leading to an instability that could be interpreted as a crossover to a strongly quantum regime where a picture of classical-like renormalized vortices is inadequate.
QUANTUM EFFECTS ON THE BEREZINSKII-KOSTERLITZ-THOULESS TRANSITION IN THE FERROMAGNETIC 2-DIMENSIONAL XXZ MODEL / A. CUCCOLI; V. TOGNETTI; P. VERRUCCHI; R. VAIA. - In: PHYSICAL REVIEW. B, CONDENSED MATTER. - ISSN 0163-1829. - STAMPA. - 51:(1995), pp. 12840-12843. [10.1103/PhysRevB.51.12840]
QUANTUM EFFECTS ON THE BEREZINSKII-KOSTERLITZ-THOULESS TRANSITION IN THE FERROMAGNETIC 2-DIMENSIONAL XXZ MODEL
CUCCOLI, ALESSANDRO;TOGNETTI, VALERIO;
1995
Abstract
The quantum easy-plane ferromagnetic two-dimensional XXZ model is approached by the pure-quantum self-consistent harmonic approximation that reduces it to an effective classical model. Quantum fluctuations weaken both the effective exchange, leading to a reduced Berezinskii-Kosterlitz-Thouless transition temperature with respect to the classical model, and the effective easy-plane anisotropy. The latter vanishes when the anisotropy is smaller than a cutoff value, leading to an instability that could be interpreted as a crossover to a strongly quantum regime where a picture of classical-like renormalized vortices is inadequate.I documenti in FLORE sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.