PHASE-DIAGRAM OF THE T-J MODEL

The t-J model is the simplest model to describe a doped Mott insulator. It is characterized by two dimensionless parameters, the ratio J/t and the electron density, n (electron/site). In 1-dim. the complete phase diagram has been determined. At values of J/t < 2, a Luttinger liquid with predominantly magnetic correlations occurs which crosses over to one with predominantly superconducting correlations at larger values of J/t. This in turn in a precursor of phase separation at J/t greater-than-or-similar-to 3. In 2-dim. Emery et al. proposed that phase separation occurs for all J/t as n --> 1. An analysis of the high temperature series supports phase separation for J/t greater-than-or-similar-to 1 but not for lower values of J/t. As in 1-dim. there are indications of a precursor region with predominantly attractive interactions. However it is not certain that this stabilizes the d-wave RVB state suggested by variational Monte-Carlo methods and cluster studies.