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Terahertz Conductivity at the Verwey Transition in Magnetite

A. Pimenov·S. Tachos·T. Rudolf·A. Loidl·D. Schrupp·M. Sing·R. Claessen·V. A. M. Brabers
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Abstract

The complex conductivity at the (Verwey) metal-insulator transition in Fe_3O_4 has been investigated at THz 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 nu_1 ~ 8 meV 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 a formation of a narrow Drude-peak with a characteristic scattering rate of about 5 meV 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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A. Pimenov, S. Tachos, T. Rudolf, A. Loidl, D. Schrupp, M. Sing, R. Claessen, V. A. M. Brabers. 2005-03-24. Terahertz Conductivity at the Verwey Transition in Magnetite. https://doi.org/10.1103/physrevb.72.035131

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