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Communications in Theoretical Physics

Phase Diagram of Random Field Spin- S Ising Model with a Transverse Field

Yu‐qiang Ma, Chang-De Gong

Published Oct 1, 1993• 0 citations
Publisher

Abstract

Random field spin- S Ising model with a transverse field has been studied by making use of the pair approximation with the discretized path-integral representation, and an analytical expression of second-order phase transition is derived for all the symmetric probability distributions of (longitudinal) random fields. The phase diagrams at T = 0 are obtained, and the conditions for existence of tricritical points are examined for an arbitrary number of nearest-neighbor spins.

DOI
10.1088/0253-6102/20/3/367

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The bimodal random field quantum spin-32\frac{3}{2}23​ Ising system is investigated by combining the pair approximation with the discretized path-integral representation. The second-order phase transition lines, and tricritical points are obtained for the bimodal random field distribution. Reentrant phase transitions, which may be caused by the competition between quantum effects and randomness, are observed. The phase diagrams with respect to the random field and the second-order phase transition temperature, i.e., (H, T) plane, are studied extensively for given values of the transverse field G and the coordination number z.
In this paper, we propose a new method, which combines the pair approximation with the discretized path-integral representation, to study the quantum transverse Ising model with random-field. Full phase diagrams are obtained for various random-field distributions. When applied random fields are trimodal (and bimodal), the critical properties including the possibility of the existence of the tricritical points and rcentrance phenomena are numerically analyzed in detail. In the limit z→∞, the extended mean-field result is recovered.