Percolative conductivity and critical exponents in mixed-valent manganites- art. no. 140418

Recent experiments have shown that some colossal magnetoresistance (CMR) ma terials exhibit a percolation transition. The conductivity exponent varies substantially with or without an external magnetic field. This finding prom pted us to carry out theoretical studies of percolation transition in CMR s ystems. We find that the percolation transition coincides with the magnetic transition, and therefore the magnetic field has a large effect on the per colation transition. Using a real-space-renormalization method and numerica l calculations for two-dimensional (2D) and three-dimensional (3D) models, we obtain the conductivity exponent t to be 5.3 (3D) and 3.3 (2D) without a magnetic field, and 1.7 (3D) and 1.4 (2D) with a magnetic field.