The Hubbard model on the kagome lattice has highly degenerate ground states (the flat lowest band) in the corresponding single-electron problem and exhibits the so-called flat-band ferromagnetism in the many-electron ground states as was found by Mielke [J. Phys. A 24, L73 (1991)]]. Here we study the model obtained by adding extra hopping terms to the above… (More)

We propose a concrete model which exhibits ferromagnetism and electron-pair condensation simultaneously. The model is defined on two chains and consists of the electron hopping term, the on-site Coulomb repulsion, and a ferromagnetic interaction which describes ferromagnetic coupling between two electrons, one on a bond in a chain and the other on a site in… (More)

In cuprate superconductors doping is believed to create holes on the O-sites, which couple antiferromagnetically with holes on the Cu-sites to form the so-called ZhangRice singlets. Here we study a d-wave pairing state based on the Zhang-Rice singlet states. Upper and lower bounds of an off-diagonal long-range order parameter with d-wave symmetry for this… (More)

An angle-resolved photoemission study of the NdB6(110) clean surface has been done in order to investigate in detail the surface electronic structure. From the dependence of the valence-band photoemission spectra on the surface condition and the exciting photon energy, we found additional peaks corresponding to the surface states on the NdB6(110) surface.… (More)

We propose a new exactly solvable model of strongly correlated electrons. The model is based on a d-p model of the CuO2 plane with infinitely large repulsive interactions on Cu-sites, and it contains additional correlated-hopping, pair-hopping and charge-charge interactions of electrons. For even numbers of electrons less than or equal to 2/3-filling, we… (More)