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Van-Nham Phan1, Holger Fehske1, and Klaus W. Becker2
1 Institut für Physik, Ernst-Moritz-Universität Greifswald, D-17487 Greifswald, Germany 2 Institut für Theoretische Physik, Technische Universität Dresden, D-01062 Dresden, Germany We explore the spontaneous formation of an excitonic insulator state at the semimetal-semiconductor transition of mixed-valence materials in the framework of the spinless Falicov-Kimball model with direct f-f- electron hopping. We also discuss the possible appearance of bound states on the semiconductor side of the transition. Adapting the projector-based renormalization method, we obtain a set of renormalization equations for the parameters of the model and derive analytical expressions for the order parameter, the renormalized electron dispersions, as well as for the wave-vector resolved single-particle spectral functions. Possible bound states are investigated on the basis of the dynamical excitonic susceptibility. |
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