Manifestation of Electron Correlations in the V₂O₃and NiS₂Systems

Abstract

The experimental manifestation of electron correlation effects in the V 2 O 3 and NiS 2 systems are reviewed, and recent elementary theories for interpreting the many different types of metal-insulator transitions based on these theories are provided. Research on the critical phenomena displayed by the interacting electrons in these systems is also reviewed.PACS numbers: 71.30.+h, 71.28.+d, 72.80.Ga Introductory commentsAmong his many scientific achievements Józef Spa lek has contributed greatly to our understanding of the experimental manifestations of electron correlation effects in solids. This has been very useful in the proper characterization of a several different metal-insulator transitions that were very puzzling at the time they were being investigated in our laboratory. It therefore seemed appropriate to selectively highlight in this article some of the key experiments, as well as their theoretical interpretation by Spa lek and collaborators.One of the hallmarks of Spa lek's work is the basic simplicity of the fundamental concepts, although the mathematical elaboration of the fine details inevitably becomes rather cumbersome. In the present, rather personalized, article we emphasize the elementary steps needed for a rationalization of selected data. The reader is urged to consult the references cited below as well as several review articles [1] for a much more balanced and complete exposition of the subject matter. Experimental dataWe begin with a brief review of experimental resistivity measurements on systems that manifest a variety of metal-insulator transitions: V 2 O 3 , Cr-and Ti-doped V 2 O 3 , nonstoichiometric V 2 O 3 , and the NiS 2 −NiSe 2 system. Work on the vanadium sesquioxide system was initiated by Foëx [2] who was the first to report a discontinuous change in electrical properties in V 2 O 3 . A highly cited set (437)