Two-Dimensional t-J Model at Low Electron Density

The phase diagram of the two-dimensional t-J model is determined accurately at low electron density by a combination of analytic and numerical techniques. The ground state exhibits three phases in the limit of zero electron density: an unpaired state at small J/t, a gas of s-wave pairs for 2 < J/t < 3.4367, and a phase separated state at larger interaction strengths. Bound states of larger clusters are never realized, and the instabilities present at small densities are discussed.