Metal-insulator transition in nanocomposites of glass and RuO2

We report on studies of interplay between percolation and quantum localization in mixtures consisting of glass grains and RuO2 metal particles of average diameters 550 and 10 nm, respectively. A weak temperature dependence of conductivity sigma(T) = a + bT(alpha), where alpha congruent to 0.20, is found in the temperature region 0.04 < T < 1 K. Similarly, an anomalously small magnitude of magnetoconductivity is observed in the studied magnetic field range up to 5 T. These observations demonstrate that percolation nature of electron transport leads to a significant modification of quantum corrections to conductivity at the localization boundary. The conductivity at criticality obeys a dynamic scaling equation with the conductivity exponent mu = 1.65 as expected for one-electron Anderson localization.