In order to investigate the crossover from a homogeneous behavior to an inhomogeneous (percolative) one, the temperature T and magnetic field H dependence of the sheet resistance R□ have been measured for two-dimensional granular aluminum films. Fitting the theory to data on magnetoconductance near TC with use of the diffusion constant D(T) as a fitting parameter, we have obtained the anomalous T-dependent diffusion constant D. From D(T), the electron diffusion index θ, a certain critical exponent in the percolation theory, has been obtained. In the relation R □-θ, the value of θ varies abruptly near 1.5 kΩ. This behavior suggests the abovementioned crossover is similar to our previous results determined from the T dependence of the upper critical magnetic field. For percolative films at H=5 T, we have found the strong R □ dependence of the prefactor αT in the expression σ=[αTe2/(2π2ℏ) ]ln T+σ0. The relation αT∝1/R □ can be explained qualitatively by a model of scaling law for percolation.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Oct 1 2004|
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics