Uniqueness of the stationary distribution and stabilizability in Zhang's sandpile model

We show that Zhang's sandpile model (N,[a,b]) on N sites and with uniform additions on [a,b] has a unique stationary measure for all 0 <= a < b <= 1. This generalizes earlier results where this was shown in some special cases. We define the infinite volume Zhang's sandpile model in dimension d >= 1, in which topplings occur according to a Markov toppling process, and we study the stabilizability of initial configurations chosen according to some measure \mu. We show that for a stationary ergodic measure \mu with density \rho, for all \rho < 1/2, \mu is stabilizable; for all \rho >= 1, \mu is not stabilizable; for 1/2 <= \rho < 1, when \rho is near to 1/2 or 1, both possibilities can occur.