Attraction between like-charged macroions by Coulomb depletion

A novel mechanism for counterion-mediated attraction between like-charged spherical macroions is proposed, which originates from a depletion zone of counterions between nearly touching macroions that is induced by Coulomb interactions. Using computer simulations of the primitive model, we show that this depletion effect dominates over the electrostatic contribution in the case of strong Coulomb coupling when all the counterions form a quasi-two-dimensional layer on the spherical macroionic surface. Its range is given by the typical spacing of counterions on the macroion surface.