The low temperature spectral weight transfer problem in Kondo insulators |
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Authors: | R Franco J Silva-Valencia and M S Figueira |
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Institution: | (1) Departamento de Física, Universidad Nacional de Colombia, A. A., 5997 Bogotá, Colombia;(2) Instituto de Física, Universidade Federal Fluminense, Av. Litoranea s/n, 24210, 346, Niterói, Rio de Janeiro, Brazil |
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Abstract: | In this paper we address the problem of the spectral weight transfer in Kondo insulators (KI). We employ the X-boson approach
for the periodic Anderson model, in the U →∞ limit. We calculate the two energy gaps of the system analytically: the indirect
gap, Δind = Eg ≃ Emir, present in the density of states, and the direct one Δdir, associated with the minimum energy necessary to produce inter-band transitions. We find that the optical behavior of the
system is governed by two energy scales: one of low frequency, characterized by Eg ≃ Emir, in the mid-infrared region (MIR), which is a reminiscent of the heavy fermion Emir peak, that appears in Kondo insulators as a broad maximum in the MIR region and that controls the low temperature transport
properties, the gap opening in optical conductivity and the formation of the Drude peak, at ω = 0, in the intermediate temperature
range. The other energy scale appears at high frequencies, and is characterized by the direct gap Δdir. According to our results, this peak controls the anomalous redistribution of spectral weight in the optical conductivity.
We apply the theory in order to study the Kondo insulator FeSi, and we calculate the optical conductivity of the system and
the spectral weight transfer in the optical conductivity. |
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Keywords: | PACS" target="_blank">PACS 75 30 Mb Valence fluctuation Kondo lattice and heavy-fermion phenomena 71 10 Ay Fermi-liquid theory and other phenomenological models 73 61 Ng Insulators 73 50 Pz Photoconduction and photovoltaic effects |
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