Intermediate valence and the possibility of a magnetic excitonic insulator

The long predicted existence of an excitonic condensed phase-i.e. the excitonic insulator-has first been verified experimentally under pressure and low temperature on the intermediate valent system TmSe/sub 0.45/Te/sub 0.55/ and TmSe/sub 0.32/Te/sub 0.68/ by Neuenschwander and Wachter (1990) and Bucher, Steiner and Wachter (1991). Now additional compounds such as Sm/sub 0.75/La/sub 0.25/S and YbO and YbS have been shown to fall under pressure into the category of excitonic insulators. The problem whether magnetism plays a role in the condensation will be discussed.<
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