Asymmetric features of various physical quantities in the normal and superconducting states between hole- and electron-doped cuprate high-temperature superconductors have been an issue of debate for a long time. Their exploration is very important for the understanding not only of the mechanism of high-Tc superconductivity but also of the nature of doped-Mott insulators. Presented in this review is the present status of theoretical understanding of the electronic states in hole- and electron-doped high- Tc cuprates as well as the origin of the electron-hole asymmetry of the electronic states. In particular, it is shown that numerically exact diagonalization calculations for small clusters in a t-J model with long-range hoppings, t and t nicely reproduce the electron-hole asymmetry observed experimentally in various quantities and thus make it possible to extract the physical origin of the asymmetry. These results give a deep insight on the asymmetric behaviors in hole- and electron-doped high-Tc cuprates and on the nature of doped Mott insulators.
We investigate how the antiferromagnetic Mott insulator evolves into the
d-wave BCS superconductor through hole doping. Allowing spin fluctuations in the strong-coupling approach, we find a spin-gapped incoherent metal with preformed pairing as an intermediate phase between the antiferromagnetic Mott insulator and
d-wave superconductor. This non-Fermi-liquid metal is identified with an infrared stable fixed point in the spin-decomposition gauge theory, analogous to the spin liquid insulator in the slave-boson gauge theory. We consider the single particle spectrum and dynamical spin susceptibility in the anomalous metallic phase, and discuss physical implications.