Document 
Eur. Phys. J. B 54, 175-183 (2006)
DOI: 10.1140/epjb/e2006-00433-1
Optical investigation of the metal-insulator transition in FeSb2
A. Perucchi1, L. Degiorgi1, Rongwei Hu2, 3, C. Petrovic2 and V.F. Mitrovic31 Laboratorium für Festkörperphysik, ETH Zürich, 8093 Zürich, Switzerland
2 Condensed Matter Physics, Brookhaven National Laboratory, Upton NY 11973, USA
3 Physics Department, Brown University, Providence RI 02912, USA
degiorgi@solid.phys.ethz.ch
(Received 10 July 2006 / Received in final form 25 August 2006 / Published online 8 December 2006)
Abstract
We present a comprehensive optical study of the narrow gap FeSb2 semiconductor. From the optical reflectivity, measured from the far infrared up to the ultraviolet spectral range, we extract the complete absorption spectrum, represented by the real part
of the complex optical conductivity. With decreasing temperature below 80 K, we find a progressive depletion of
below
cm-1, the semiconducting optical gap. The suppressed (Drude) spectral weight within the gap is transferred at energies
and also partially piles up over a continuum of excitations extending in the spectral range between zero and Eg. Moreover, the interaction of one phonon mode with this continuum leads to an asymmetric phonon shape. Even though several analogies between FeSb2 and FeSi were claimed and a Kondo-insulator scenario was also invoked for both systems, our data on FeSb2 differ in several aspects from those of FeSi. The relevance of our findings with respect to the Kondo insulator description will be addressed.
71.27.+a - Strongly correlated electron systems; heavy fermions.
71.30.+h - Metal-insulator transitions and other electronic transitions.
75.30.Mb - Valence fluctuation, Kondo lattice, and heavy-fermion phenomena.
78.20.-e - Optical properties of bulk materials and thin films.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2006