V.J. Emery, S.A. Kivelson, H.Q. Lin, "Phase separation in the t-J Model," Physical Review Letters, 64:475-78, 1990.
Victor J. Emery (Brookhaven National Laboratory, Upton, N.Y.): "The t-J model of high-temperature superconductors regards the copper oxide planes as a background array of spins--antiferromagnetically coupled via an exchange integral J--and the charge carriers as `holes' (or missing spins) hopping from one site to another with amplitude t.
"In this article we present analytical and numerical arguments to show that the ground state does not have uniform charge density. Rather, the holes separate into two phases: one hole-rich, the other free of holes. It has since been shown that phase separation occurs for various other models, and it is coming to be regarded as a significant element in the puzzle of high-temperature superconductivity.
"We have gone on to show that long-range Coulomb forces prevent full-phase separation, but leave fluctuating droplets of one phase...