Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2005-03-24
Phys. Rev. B 72, 035131 (2005)
Physics
Condensed Matter
Strongly Correlated Electrons
6 Pages, 3 Figures
Scientific paper
10.1103/PhysRevB.72.035131
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.
Brabers V. A. M.
Claessen Ralph
Loidl Alois
Pimenov Andrei
Rudolf Torsten
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