Europhys. Lett.
Volume 70, Number 6, June 2005
Page(s) 789 - 795
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 25 May 2005
Europhys. Lett., 70 (6), pp. 789-795 (2005)
DOI: 10.1209/epl/i2005-10045-y

High-energy photoemission on $\chem{Fe_3 O_4}$: Small polaron physics and the Verwey transition

D. Schrupp1, M. Sing1, 2, M. Tsunekawa2, H. Fujiwara2, S. Kasai2, A. Sekiyama2, S. Suga2, T. Muro3, V. A. M. Brabers4 and R. Claessen1

1  Experimentalphysik II, Universität Augsburg - D-86135 Augsburg, Germany
2  Division of Material Physics, Graduate School of Engineering Science Osaka University - Toyonaka, Osaka 560-8531, Japan
3  Japan Synchrotron Radiation Research Institute, SPring-8 Sayo-gun, Hyogo 679-5198, Japan
4  Department of Physics, Eindhoven University of Technology 5600 MB Eindhoven, The Netherlands

received 14 February 2005; accepted in final form 22 April 2005
published online 25 May 2005

We have studied the electronic structure and charge ordering (Verwey) transition of magnetite ( $\chem{Fe_3 O_4}$) by soft X-ray photoemission. Due to the enhanced probing depth and the use of different surface preparations we are able to distinguish surface and volume effects in the spectra. The pseudogap behavior of the intrinsic spectra and its temperature dependence give evidence for the existence of strongly bound small polarons consistent with both dc and optical conductivity. Together with other recent structural and theoretical results our findings support a picture in which the Verwey transition contains elements of a cooperative Jahn-Teller effect, stabilized by local Coulomb interaction.

71.30.+h - Metal-insulator transitions and other electronic transitions.
71.38.Ht - Self-trapped or small polarons.
79.60.-i - Photoemission and photoelectron spectra.

© EDP Sciences 2005