Physics – Condensed Matter – Disordered Systems and Neural Networks
Scientific paper
2003-06-26
Phys. Rev. B vol.68, 024207 (2003)
Physics
Condensed Matter
Disordered Systems and Neural Networks
8 pages, 5 figures (Phys. Rev. B - 1 August 2003)(fig1 replaced)
Scientific paper
10.1103/PhysRevB.68.024207
We propose a theory of the origin of transport nonuniversality in disordered insulating-conducting compounds based on the interplay between microstructure and tunneling processes between metallic grains dispersed in the insulating host. We show that if the metallic phase is arranged in quasi-one dimensional chains of conducting grains, then the distribution function of the chain conductivities g has a power-law divergence for g -> 0 leading to nonuniversal values of the transport critical exponent t. We evaluate the critical exponent t by Monte Carlo calculations on a cubic lattice and show that our model can describe universal as well nonuniversal behavior of transport depending on the value of few microstructural parameters. Such segregated tunneling-percolation model can describe the microstructure of a quite vast class of materials known as thick-film resistors which display universal or nonuniversal values of t depending on the composition.
Grimaldi Claudio
Maeder Thomas
Ryser Peter
Straessler Sigfrid
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