Berlin 2008 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 14: Electronic Properties I
MM 14.2: Talk
Monday, February 25, 2008, 17:00–17:15, H 0111
Spectral-weight analysis from ellipsometric spectroscopy on FeSi single crystals — •Dirk Menzel1, Paul Popovich2, Alexander Boris2, Ana Maria Racu1, and Joachim Schoenes1 — 1TU Braunschweig, Institut für Physik der Kondensierten Materie — 2Max-Planck-Institut für Festkörperforschung, Stuttgart
One of the key arguments of the supporters of the description of FeSi as Kondo insulator stems from reflectivity measurements. After Kramers-Kronig analysis (KKR) of these data the resulting optical conductivity spectra in some cases [1] show a loss of spectral weight when the gap opens at low temperature, which is not recovered in the neighborhood of the gap, while in some cases it does not [2]. Since the determination of absolute conductivity values from reflectivity spectra is problematic, we have undertaken ellipsometry measurements from the far-infrared to the UV spectral range, giving directly - without KKR - the optical conductivity. We find that the spectral weight is not compensated up to 2.5 eV. At low temperatures the indirect gap amounts to 33 meV and is filled at a temperature of about 250 K. This is in agreement with our recent Raman investigations indicating a change in the effective masses of the charge carriers as function of temperature which results in a shift of the chemical potential towards the valence band [3]. It is discussed if an interaction among d-electrons can be the origin of the widely spread spectral-weight recovery.
[1] Z. Schlesinger et al., Phys. Rev. Lett. 71, 1748 (1993).
[2] L. Degiorgi et al., Europhys. Lett. 28, 341 (1994).
[3] A. M. Racu et al., Phys. Rev. B 76, 115103 (2007).