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TT: Fachverband Tiefe Temperaturen
TT 27: CE: Poster Session
TT 27.44: Poster
Wednesday, March 24, 2010, 14:00–18:00, Poster D1
On the existence of the excitonic insulator phase in the extended Falicov-Kimball model: a vectorial slave-boson approach — •Bernd Zenker1, Dieter Ihle2, Franz Xaver Bronold1, and Holger Fehske1 — 1Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, 17489 Greifswald, Germany — 2Institut für Theoretische Physik, Universität Leipzig, 04109 Leipzig, Germany
Motivated by the possibility of pressure-induced exciton condensation in intermediate-valence Tm[Se,Te] compounds we study the Falicov-Kimball model extended by a finite f-hole valence bandwidth. Within slave-boson mean-field theory we show that coherence between c- and f-states may be established at low temperatures, leading to an excitonic insulator (EI) phase. Thereby our vectorial slave-boson approach overcomes (i) the difficulties of the scalar slave-boson scheme by describing the EI state, and yields (ii) a substantial reduction of the critical temperatures in comparison to those of the standard Hartree-Fock approach. Analyzing the partial densities of states we find strong evidence that the EI typifies either a BCS condensate of electron-hole pairs (weak-coupling regime) or a Bose-Einstein condensate (BEC) of preformed excitons (strong-coupling regime), which points towards a BCS-BEC transition scenario as Coulomb correlations increase.