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The European Physical Journal B
ISSN: 1434-6028 (printed version)
ISSN: 1434-6036 (electronic version)
Abstract Volume 1 Issue 1 (1998) pp 103-106
Quantum spherical $\mathsf{XY}$ model in a random field: coherent state path integral approach
Y.Q. Ma (1)(2) (a), W. Figueiredo (2)
(1) Department of Physics, Nanjing University, Nanjing 210093, China
(2) Departamento de Fisica, Universidade Federal de Santa Catarina, 88040-900, Florianopolis, Santa Catarina, Brazil
Received: 20 May 1997 / Accepted: 20 October 1997
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 ${\Delta}$ on the possibilities of the existence of a ferromagnetic phase are discussed. At the critical point, ${\Delta}_{\rm c}$, the order parameter M describing the ordered ferromagnetic phase disappears as $\propto ({\Delta}_{\rm c} - {\Delta})^{{1}/{2}}$.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 $\mu ={J_{0}}/{2}$, 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 $({J_{0}}/{2T}) \exp (-{J_{0}}/{2T})$ and $({J^{2}_{0}}/{4T^{2}}) \exp (-{J_{0}}/{2T})$, respectively.
PACS. 75.10.-b General theory and models of magnetic ordering
(a) e-mail: myqiang@netra.nju.edu.cn
Online publication: February 4, 1998
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