im Sommersemester 2002
Im Berliner Physikalischen Kolloquium im Magnus-Haus hat
Prof. Dr. Peter Wachter,
Laboratorium für Festkörperphysik, Eidgenössische Technische Hochschule (ETH), Zürich, Schweiz,
vorgetragen.
Titel, Termin, Moderation und Ort
| Titel: | Intermediate valent Tm compounds: A superfluid in a condensed excitonic state |
| Termin: | Donnerstag, 11. April 2002, 19:30 Uhr |
| Moderation: | Wolfgang Nolting (HU Berlin) |
| Ort: | Magnus-Haus Am Kupfergraben 7 10117 Berlin |
Zusammenfassung
Exciton condensation in the form of an excitonic insulator has been postulated by Mott already in 1961. The experimental realization of such a state in intermediate valent TmSe1-xTex compounds, however, had to wait until 1990 [J. Neuenschwander, P. Wachter, Phys. Rev. B 41, 12693 (1990)]. Now it appears essential that an intermediate valent state is a prerequisite for the exciton condensation because a narrow hybridized 4f band is necessary. The new and exciting facts are thermodynamic measurements on TmSe0.45Te0.55 single crystals at low temperatures and high pressure. At ambient conditions this material is a narrow gap semiconductor which can be transformed under high pressure (14 kbar) into an intermediate valent metal. Below 250 K and between 5 and 13 kbar the excitonic state is formed. In this case, the thermal conductivity shows a behavior which has only been observed so far in the superfluid phase of He II.