Electrical conductivity and metal-insulator transition in the amorphous system Cr_xGe_1-x

Abstract

Amorphous films of the system Ge_1-xCr_x with x = 0·04–0·25 have been prepared by electron-beam evaporation and their electrical conductivity in the as-grown state measured in the temperature range T = 50 mK-300 K. The critical concentration for the metal-insulator transition (MIT) was found to be x_c = 0·10. For x < 0.10 the low-temperature conductivity obeys the law σ(T) = σ₁ exp {−(T₀/T)^½} for T < 50 K. For x > 0.13 the conductivity up to T ≈ 250K follows the relation σ(T)=σ₀ +βT ^½+γT For 0·10<x<0·20 a new conductivity mechanism is observed at low-temperatures. The results are discussed with respect to the MIT and Mott's minimum metallic conductivity.