Effect of localized and delocalized electrons on the low-temperature conductivity and magnetoconductivity of metallic Ge homogeneously doped by As

At T = 20 mK-2 K we analyze the temperature dependence of conductivity and magnetoconductivity of a series of metallic samples of Ge:As close to the critical free carrier concentration n(c) congruent to 3.5 x 10(17) cm(-3) of the metal-insulator transition. At it less than or equal to 5.7 x 10(17) cm(-3) we find a logarithmic correction to the conductivity instead of sigma proportional to T-1/2 found at higher it. The conductivity as well as the anomalous positive magnetoresistivity can be interpreted as a Kondo-like effect of localized and delocalized electrons with an antiferromagnetic exchange interaction slightly above n(c). (C) 2000 Elsevier Science B.V, All rights reserved.