Doping dependence of electronic excitations in high Tc superconducting cuprates

The single-particle excitation spectrum is studied in the two-dimensional (2D) t–t′–t′′–J model with t, t′, t′′ and J being the first, second and third nearest neighbor hopping parameters of carriers and the nearest neighbor antiferromagnetic interaction, respectively, by using the numerically exact diagonalization method of small clusters. For a set of the parameter values, the momentum dependent spectrum is calculated as a function of hole-carrier density. It is found that the calculated results explain the experimental data of angle-resolved photoemission spectroscopy (ARPES) experiments for insulating Sr2CuO2Cl2 and hole-doped Bi2212, both underdoped and overdoped. The spectrum in electron-doped cuprates is also studied. The results indicate that the electronic structure in the insulating parent materials is essentially the same as that in the high Tc ones, and that the carrier density and the sign of the charge are the physical parameters to control the physical properties.