Exciton condensation in an intermediate valence compound: TmSe0.45Te0.55

Exciton condensation has been realized at low temperatures and high pressur e in several intermediate valence compounds with Tm and Sm such as TmSe0.45 Te0.55, TmSe0.32Te0.68, Sm0.90La0.10S, Sm0.75La0.25S, Sm0.65La0.35S, Sm0.85 Tm0.15S, Sm0.75Tm0.25S. The most pronounced effects, however, are found in TmSe0.45Te0.55. In this material a high pressure isobar and a low temperatu re isotherm have been measured, which provide strong evidence for the excit on condensation. An extremely soft state is observed in a particular pressu re range at room temperature, while at low temperature the material is near ly as hard as diamond. (C) 2001 Published by Elsevier Science Ltd.