Spectra of the high Tc cuprates understood by the variational studies of the t–J-type models

Trial wavefunctions with and without antiferromagnetic order for the 2-dimensional t–J-type model are proposed to describe the low-energy states of high Tc cuprates with doped holes or electrons. In the slightly doping regime, we found states behaving like charged quasi-particles with well-defined momenta and having much less pairing correlations than previously studied ones. There exist also states showing the incoherent and ‘spin-bag’ behaviors. Our results are supported by exact calculation and are consistent with recent photoemission experiments. With increasing doping, superconducting states emerge and behave similarly with that described in recent band-structure analysis and seen in various materials.