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

Exciton condensation has been realized at low temperatures and high pressure in several intermediate valence compounds with Tm and Sm such as TmSe0.45Te0.55, TmSe0.32Te0.68, Sm0.90La0.10S, Sm0.75La0.25S, Sm0.65La0.35S, Sm0.85Tm0.15S, Sm0.75Tm0.25S. The most pronounced effects, however, are found in TmSe0.45Te0.55. In this material a high pressure isobar and a low temperature isotherm have been measured, which provide strong evidence for the exciton condensation. An extremely soft state is observed in a particular pressure range at room temperature, while at low temperature the material is nearly as hard as diamond.