Positive magnetoresistance in a weak magnetic field in germanium with impurity concentration near the metal‐insulator transition

Abstract

On the metallic side of the metal-insulator transition (MIT) the theory of quantum corrections to the conductivity provides an accurate description of the temperature dependence of conductivity and magnetoconductivity in a wide variety of disordered conductors. However, we found that there exists a concentration region 1 ≤ N/Nc < 1.4 (here Nc is the critical concentration of the MIT) where the quantum interference corrections do not manifest themselves in the low-temperature resistivity and magnetoresistance experiments. Experiments have been done on isotopically engineered bulk n-type Ge with a high homogeneity of the impurity distribution, which was obtained by neutron-transmutation doping on the metallic side of the MIT close to Nc. We observed an abnormal positive magnetoresistance at relatively small magnetic fields and low temperatures (down to 30 mK) which we consider to be due to the Maki-Thomson correction to the metallic conductivity [1] and a second contribution which we attribute to be due to the tunneling between neighboring electron lakes localized in long range potential fluctuations. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)