Antiferromagnetic Insulators

In this book we treat the discontinuous nature of the transition using an analysis introduced by Brinkman and Rice (1970a, b). This applies to bandcrossing transitions and transitions in an array of one-electron centres. We term the latter Mott transitions when the centres have a moment we do not limit the term to cases when the moment is that of a single spin, and indeed such cases are rare (Chapter 3). The insulating antiferromagnetic state is sometimes called a Mott insulator . A Mott transition can be accompanied by a change of structure (see Section 3 below). 

Figure 8,5 The insulating antiferromagnetic and superconducting phase region for La Sr CuO,...

An interesting subset of the 214 phases are the (R,Ce)2Cu04 materials, where usually R=Nd or Pr. These were initially studied as the only conduction-electron high-T superconductors (in all others, holes are the charge carriers). As usually prepared, insulating antiferromagnetic behavior is retained as cerium is added to the end-point... 

Strongly Correlated Systems. The third class of systems for which the LDA and the GGA have fundamental problems are strongly correlated systems. The most prominent examples of such systems are the 3d transition metal monoxides MnO, FeO, CoO, and NiO. These systems, which crystallize in the rock salt structure, are insulating antiferromagnets of type II (Mott insulators). Both the LDA and the GGA, on the other hand, predict FeO and CoO to be metallic and by far underestimate the band gap in MnO and NiO [35,36,37]. This is illustrated in Fig. 2.2 in which the LDA band structure for FeO is plotted - the band structures obtained with the most frequently applied GGAs are rather similar to their LDA counterpart [36,37]. 

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