  The anisotropic d=3 tJ model is studied by renormalization-group theory,
yielding the evolution of the system as interplane coupling is varied from the
isotropic three-dimensional to quasi-two-dimensional regimes.
Finite-temperature phase diagrams, chemical potential shifts, and in-plane and
interplane kinetic energies and antiferromagnetic correlations are calculated
for the entire range of electron densities. We find that the novel tau phase,
seen in earlier studies of the isotropic d=3 tJ model, and potentially
corresponding to the superconducting phase in high-T_c materials, persists even
for strong anisotropy. While the tau phase appears at low temperatures at
30-35% hole doping away from <n_i>=1, at smaller hole dopings we see a complex
lamellar structure of antiferromagnetic and disordered regions, with a
suppressed chemical potential shift, a possible marker of incommensurate
ordering in the form of microscopic stripes. An investigation of the
renormalization-group flows for the isotropic two-dimensional tJ model also
shows a pre-signature of the tau phase, which appears with finite transition
temperatures upon addition of the smallest interplane coupling.
