PHASE STRING EFFECT IN WEAKLY DOPED ANTIFERROMAGNET

Spiral instabilities usually obscure theoretical attempt to get into m etallic phase by doping. A recently revealed nonlocal phase string eff ect indicates such spiral effect to be artificial due to an illegitima te mean-field treatment. We present a self-consistent theory which inc orporates the nonlocal phase string effect into a bosonic resonating-v alence-bond (RVB) description and show a continuous evolution into a m etallic phase, where magnetic anomalies in spin susceptibility and NMR are found consistent with experiment and superconducting condensation is always present at low-temperature. A unified phase diagram for the weakly doped t-J model is given, in which an underdoped metallic phas e with charge inhomogeneity is also briefly discussed.