Underdoping versus optimum-doping: A bosonic RVB understanding

We propose that the bosonic RVB description of spins and the phase string e ffect of doping constitute two crucial factors in the weakly-doped t-J mode l. Within this framework, a charge inhomogeneity solution is found in the u nderdoped metallic phase, characterized by a double-peak energy structure i n dynamic spin susceptibility in contrast to a single 'resonance-like' peak below T-c at 'optimum'-doping. Comparisons with recent experimental measur ements on cuprates are made. (C) 1998 Elsevier Science Ltd. All rights rese rved.