Variational cluster approach to the extended Falicov-Kimball model: A BCS-BEC crossover in the Excitonic insulators

We study the Coulomb-interaction induced spontaneous symmetry breaking of the excitonic insulator state in the two-dimensional extended Falicov-Kimball model. Using the variational cluster approximation, we evaluate the order parameter, single-particle excitation gap, momentum distribution functions...

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Bibliographic Details
Published inJournal of physics. Conference series Vol. 391; no. 1; pp. 12147 - 4
Main Authors Seki, K, Kaneko, T, Yamaki, S, Eder, R, Ohta, Y
Format Journal Article
LanguageEnglish
Published Bristol IOP Publishing 01.01.2012
Subjects
Approximation
BCS theory
Broken symmetry
Clusters
Distribution functions
Excitation
Fermi surfaces
Green's functions
Insulators
Mathematical analysis
Mathematical models
Order parameters
Physics
Two dimensional models
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Summary:We study the Coulomb-interaction induced spontaneous symmetry breaking of the excitonic insulator state in the two-dimensional extended Falicov-Kimball model. Using the variational cluster approximation, we evaluate the order parameter, single-particle excitation gap, momentum distribution functions, and anomalous Green's function as a function of U at zero temperature. We find that in the weak-to-intermediate couplinb regime, the Fermi surface is well-defined and the calculated results can be understood in the close correspondence with the BCS theory, whereas in the strong-coupling regime, the Fermi surface is ill-defined and the results are consistent with the picture of BEC.
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ISSN:1742-6588
1742-6596
DOI:10.1088/1742-6596/391/1/012147