Electrical and magnetoconductivity of binary and Fe-doped a-Re_xSi_1-x thin films near the metal-insulator transition

The low-temperature electrical transport behavior of amorphous Re_xSi_1-x and Re_xFe_ySi_1-x-y thin films has been investigated as a function of temperature and magnetic field on the metallic side of the metal-insulator transition (MIT). In the temperature range above 20 K both undoped and Fe-doped films show the same approximately linear behavior of conductivity up to 300 K. At temperatures below 20 K the conductivity of the Re_xSi_1-x system can be understood on the basis of the theory of quantum corrections to the conductivity: The temperature dependence of the conductivity and the negative magnetoconductivity are caused by electron-electron interactions. The conductivity of Fe-doped films shows a completely different behavior. The comparison of undoped and Fe-doped films at the same σ(0) demonstrates that the width of the density of states anomaly near the Fermi energy Δ differs by two orders of magnitude. The positive contribution to the magnetoconductivity increasing strongly with decreasing temperature can be explained within a model of bound magnetic polarons and is related to additional spin scattering.