Issue Eur. Phys. J. B Volume 54, Number 2, November II 2006 Page(s) 175 - 183 DOI 10.1140/epjb/e2006-00433-1 Published online 08 December 2006

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 Hu^{2, 3}, C. Petrovic² and V.F. Mitrovic<sup>3

1</sup>  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 E_g. 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.

PACS
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

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