Bound state formation and nature of the excitonic insulator phase in the extended Falicov-Kimball model

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. Calculating the Frenkel-type exciton propagator we obtain excitonic bound states above a characteristic...

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Bibliographic Details
Published in:arXiv.org 2008-09
Main Authors: Ihle, D, Pfafferott, M, Burovski, E, Bronold, F X, Fehske, H
Format: Article
Language:English
Subjects:
Condensates
Coupling
Excitons
Holes (electron deficiencies)
Quantum theory
Online Access:Get full text
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Summary: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. Calculating the Frenkel-type exciton propagator we obtain excitonic bound states above a characteristic value of the local interband Coulomb attraction. Depending on the system parameters coherence between c- and f-states may be established at low temperatures, leading to an excitonic insulator phase. We find strong evidence that the excitonic insulator 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.
ISSN:2331-8422
DOI:10.48550/arxiv.0807.4616