Abstract With cuprate superconductors in mind, we study the effects of point-type impurity potential (V) on a d x 2−y 2 -wave superconducting (d-SC) state in a strongly correlated squarelattice Hubbard model (U/t = 12) with a diagonal transfer (t′), using a variational Monte Carlo method. At half filling, insulator-to-conductor (filling-control-type Mott) transitions occur at <?CDATA
V=VU(±)∼±U?> V = V U ( ± ) ∼ ± U . The phase realized for <?CDATA
V<VU(−)?> V < V U ( − ) is robust d-SC and the charge carriers are holes, whereas for <?CDATA
V>VU(+)?> V > V U ( + ) a metallic (or weak d-SC) state appears with charge carriers of electrons. For a partially-filled case where the impurity density is equal to the doping rate, a d-SC-to-insulator transition arises at V ≡ V M ∼ 4t. In the weak-|V| phases, the impurity effects in the electron distribution are smeared out by the screening effect, whereas in the strong-|V| phases, the electron distribution directly depend on the impurity configurations.
We study the spectral weight transfer and the chemical potential shift in strongly correlated electron systems caused by carrier doping by applying the dynamical mean-field theory to a two-band Hubbard model. The parameters of the model are chosen so that the undoped system is a charge-transfer-type insulator. We find that in the insulating phase there are finite intensities corresponding to local singlet states formed by hybridized d and p electrons, and that, on doping a part of them, turn into itinerant states. The results are discussed in the light of experimental and theoretical results for high-
Tc cuprates. \textcopyright{} 1996 The American Physical Society.