Eur. Phys. J. B 1, 103-106 (1998)
https://doi.org/10.1007/s100510050157

Quantum spherical XY model in a random field: coherent state path integral approach

¹ Department of Physics, Nanjing University, Nanjing 210093, China
² Departamento de Fisica, Universidade Federal de Santa Catarina, 88040-900, Florianopolis, Santa Catarina, Brazil

Corresponding author: ^a myqiang@netra.nju.edu.cn

Received: 20 May 1997
Accepted: 20 October 1997
Published online: 15 January 1998

Abstract

By introducing boson operators, a quantum spherical XY model in the presence of a random field has been studied by the coherent state path integral approach. The phase diagram is obtained, and the effects of the random-field fluctuations Δ on the possibilities of the existence of a ferromagnetic phase are discussed. At the critical point, Δ_c, the order parameter M describing the ordered ferromagnetic phase disappears as ∝(Δ_c-Δ)^1/2. Since the model is equivalent to a Bose system, we also show that the phase transition at zero temperature between the superfluid and the disordered Mott insulator phases occurs at the chemical potential μ=J₀/2, where J₀ is the strength of the exchange interaction. As the temperature T goes to zero, the asymptotic behavior of the entropy and the specific heat are (J₀/2T) exp (-J₀/2T) and (J²₀/4T²) exp (-J₀/2T), respectively.