Terahertz conductivity at the Verwey transition in magnetite

A. Pimenov, S. Tachos, T. Rudolf, A. Loidl, D. Schrupp, M. Sing, R. Claessen, and V. A. M. Brabers
Phys. Rev. B 72, 035131 – Published 29 July 2005

Abstract

The complex conductivity at the (Verwey) metal-insulator transition in Fe3O4 has been investigated at terahertz and infrared frequencies. In the insulating state, both the dynamic conductivity and the dielectric constant reveal a power-law frequency dependence, the characteristic feature of hopping conduction of localized charge carriers. The hopping process is limited to low frequencies only, and a cutoff frequency ν18meV must be introduced for a self-consistent description. On heating through the Verwey transition the low-frequency dielectric constant abruptly decreases and becomes negative. Together with the conductivity spectra this indicates the formation of a narrow Drude peak with a characteristic scattering rate of about 5meV containing only a small fraction of the available charge carriers. The spectra can be explained assuming the transformation of the spectral weight from the hopping process to the free-carrier conductivity. These results support an interpretation of Verwey transition in magnetite as an insulator-semiconductor transition with structure-induced changes in activation energy.

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  • Received 25 March 2005

DOI:https://doi.org/10.1103/PhysRevB.72.035131

©2005 American Physical Society

Authors & Affiliations

A. Pimenov, S. Tachos, T. Rudolf, and A. Loidl

  • Experimentalphysik V, EKM, Universität Augsburg, 86135 Augsburg, Germany

D. Schrupp, M. Sing, and R. Claessen

  • Experimentalphysik II, Universität Augsburg, 86135 Augsburg, Germany

V. A. M. Brabers

  • Department of Physics, Eindhoven University of Technology, NL-5600, MB Eindhoven, The Netherlands

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Issue

Vol. 72, Iss. 3 — 15 July 2005

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