Spin Glasses, Orientational Glasses and Random Field Systems

Abstract

In this chapter, we draw attention to {Monte} {Carlo} simulations of various kinds of disordered solids, where, due to the preparation of the sample, structural disorder is frozen in (''quenched disorder''). Typically, these systems are produced by random dilution of different atomic species. This structural disorder introduces disorder in the effective interactions responsible for the ordering of the system; it may be of the ''random bond''-type or of the ''random field''-type. If this disorder is very strong, it may give rise to qualitatively new types of ordering phenomena such as spin glasses [12.1-4] in the case of magnetic systems and, most recently, vortex glasses [12.5] in the case of superconductors, etc. For many such problems analytical methods can only give very restricted information, and hence simulations are very important. We start by reviewing recent work on spin glasses (sect. 12.1) and discuss an interesting generalisation, the potts glass, in sect. 12.2. The latter model can be viewed as a model of an anisotropic quadrupolar glass (or orientational glass, respectively). Isotropic orientational glasses are then treated in sect. 12.3, focusing attention on ''random bond'' disorder throughout. Sect. 12.4 summarises work on the random field {Ising} problem, while sect. 12.5 contains a discussion as well as an outlook to other related problems not treated in the present article, such as simulations of structural glasses and their glass transitions. In this chapter, we do not attempt to give a complete survey, but restrict ourselves to a description of the main directions.