Inhomogeneous sandpile model: Crossover from multifractal scaling to finite-size scaling

Abstract

We study an inhomogeneous sandpile model in which two different toppling rules are defined. For any site only one rule is applied corresponding to either the Bak, Tang, and Wiesenfeld model [P. Bak, C. Tang, and K. Wiesenfeld, Phys. Rev. Lett. 59, 381 (1987)] or the Manna two-state sandpile model [S. S. Manna, J. Phys. A 24, L363 (1991)]. A parameter c is introduced which describes a density of sites which are randomly deployed and where the stochastic Manna rules are applied. The results show that the avalanche area exponent tau a, avalanche size exponent tau s, and capacity fractal dimension Ds depend on the density c. A crossover from multifractal scaling of the Bak, Tang, and Wiesenfeld model (c = 0) to finite-size scaling was found. The critical density c is found to be in the interval 0 < c < 0.01. These results demonstrate that local dynamical rules are important and can change the global properties of the model.