Dresden 2009 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 35: Poster Session II
MM 35.6: Poster
Mittwoch, 25. März 2009, 16:30–18:30, P4
Electron-phonon interaction and spectral weight transfer in Fe1−xCoxSi — •Paul Popovich1, Dirk Menzel2, Natalia Kovaleva1, Joachim Schoenes2, Klaus Doll1, and Alexander Boris1 — 1Max Planck Institute for Solid State Research, Heisenbergstr. 1, D-70569 Stuttgart, Germany — 2Institut für Physik der Kondensierten Materie, TU Braunschweig, Germany
The unusual properties of the narrow-gap semiconductor FeSi continue to attract attention of many theoreticians and experimentalists due to its similarities with some rare-earth compounds known as Kondo insulators. We present a comprehensive ellipsometric study on Fe1−xCoxSi single crystals (x=0-0.2) in the spectral range from 0.01 to 6.2 eV. Direct and indirect band gaps of 73 meV and 10 meV, respectively, are observed in FeSi at 7 K. Four infrared active modes are assigned at 206, 329, 352, and 458 cm−1 for FeSi. Two of them are asymmetric at low temperatures, reflecting the phonon-phonon and electron-phonon coupling in the system. As temperature increases, the indirect gap changes sign manifesting semiconductor to semimetal crossover. The corresponding spectral weight gain at low energies is recovered within an energy range of several eV. The present findings imply that the electron-phonon interaction and semimetallic character of FeSi play the dominant role in the broad-band spectral weight transfer and strongly support the model that Fe1−xCoxSi can be well described in an itinerant picture taking into account self-energy corrections.