Resonating Hartree--Fock Studies on the Electronic Structures of the Two-Dimensional Hole-Doped Hubbard Model

Electronic structures of the two-dimensional doped Hubbard model are investigated by using the resonating Hartree--Fock method. It is shown that doped holes form polarons in a wide range of doping regions relevant to superconductivity. The momentum distribution of electrons and the spin correlation function indicate that carriers change from polarons to conventional holes as we enhance hole doping. We will visualize quantum fluctuations in these electronic states by analyzing the structures of the Slater determinants generating the resonating Hartree--Fock wave functions.