For spin systems with random, finite-range interactions, we define
an analog of the usual weak mixing property, which we call “weak mixing
in expectation” (WME). This property implies (almost sure) uniqueness of
the Gibbs measure.
¶ We concentrate on the two-dimensional case, for which we present
finite-volume conditions which are sufficient for WME. We also show the
reverse: if the system is WME, then the condition is satisfied for some
(sufficiently large) volume. Simultaneously, we obtain an extension (to random
interactions) of the result by Martinelli, Olivieri and Schonmann that weak
mixing implies strong mixing.
¶ Our method is based on a rescaled version of the disagreement
percolation approach of van den Berg and Maes, combined with ideas and
techniques of Gielis and Maes, and Martinelli, Olivieri and Schonmann. However,
apart from some general results on coupling, stated in Section 2, this paper is
self-contained.