Hopping conductivity in Cr-doped ß-FeSi single crystals

The resistivity of Cr-doped p -type ß- Fe Si2 single crystals has been investigated in the temperature interval of T=4.2-300 K. The data are analyzed within the framework of the variable-range hopping (VRH) mechanism for both the Mott and the Shklovskii-Efros regimes. With decreasing temperature a crossover between the Mott and the Shklovskii-Efros VRH conductivity regimes is observed. It is shown that the temperature dependence of the resistivity, ρ (T), of Cr-doped ß-Fe Si2 crystals, that follows a VRH conductivity mechanism, obeys a scaling law ln (ρ ρ 0) =Af (T Tx). The values of the characteristic (T0) and the transition temperatures (Tv), as well as the width of the soft Coulomb gap Δ in the spectrum of the density of the localized states (DOS) are determined. The observed values of the VRH transition and characteristic temperatures indicate the existence of a rigid gap δ in the spectrum of the DOS in addition to Δ. This points to the polaronic nature of the charge carriers in the investigated compound. © 2005 American Institute of Physics.