Seiji Yunoki

Unconventional metal-insulator transition in two dimensions

We show, by using a correlated Jastrow wave function and a mapping onto a classical model, that the two-dimensional Mott transition in a simple half-filled one-band model can be unconventional and very similar to the binding-unbinding Kosterlitz-Thouless transition of vortices and antivortices, here identified by empty and doubly occupied sites. Within this framework, electrons strongly interact with collective plasmon excitations that induce anomalous critical properties on both sides of the transition. In particular, the insulating phase is characterized by a singular power-law behavior in the photoemission spectrum, which can be continuously connected to the fully projected insulating state relevant to strongly correlated low-energy models.

Spin-flux phase in the Kondo lattice model with classical localized spins

We provide numerical evidence that a spin-flux phase exists as a ground state of the Kondo lattice model with classical local spins on a square lattice. This state manifests itself as a double-e magnetic order in the classical spins with spin density at both (0, pi) and (pi ,0) and further exhibits fermionic spin currents around an elementary plaquette of the square lattice. We examine the spin-wave spectrum of this phase. We further discuss an extension to a face-centered-cubic (fcc) lattice where a spin-flux phase may also exist. On the fee lattice the spin-flux phase manifests itself as a triple-Q magnetically ordered state and may exist in gamma -Mn alloys.

Robust D-Wave Pairing Correlations in a Hole-Doped Spin-Fermion Model

Pairing correlations are studied numerically in a hole-doped spin-fermion model. Simulations performed on up to 12 x 12 clusters provide indications of D-wave superconductivity away from half-filling comparable to those of the 2D t-J model. The pairing correlations are the strongest in the direction perpendicular to the dynamic stripes that appear in the ground state at some densities. An optimal doping, where correlations are maximized, was observed at approximately 25% doping with an estimated T(c) approximately 100-200 K, in qualitative agreement with high-T(c) cuprates phenomenology, while pairing correlations are suppressed by static stripe inhomogeneities.

Role of Strong Correlation in the Recent Angle-Resolved Photoemission Spectroscopy Experiments on Cuprate Superconductors

Motivated by recent photoemission experiments on cuprates, the low-lying excitations of a strongly correlated superconducting state are studied numerically. It is observed that along the nodal direction these low-lying one-particle excitations show a linear momentum dependence for a wide range of excitation energies and, thus, they do not present a kink-like structure. The nodal Fermi velocity

Coherent inverse photoemission spectrum for Gutzwiller projected superconductors

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Single-particle anomalous excitations of Gutzwiller-projected BCS superconductors and Bogoliubov quasiparticle characteristics

, as well as other observables, are systematically evaluated directly from the calculated dispersions, and they are found to compare well with experiments. It is argued that the parameter dependence of

Resonating valence bond wave function : from lattice models to realistic systems

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Resonating Valence Bond Wave Function for the Two-Dimensional Fractional Spin Liquid

is quantitatively explained by a simple picture of a renormalized Fermi velocity.

From Luttinger liquid to Mott insulator : The correct low-energy description of the one-dimensional hubbard model by an unbiased variational approach

Rigorous relations for Gutzwiller projected BCS states are derived. The obtained results do not depend on the details of model systems, but solely on the wave functions. Based on the derived relations, physical consequences are discussed for strongly correlated superconducting states such as high-

Electron–hole asymmetry in magnetic properties of lightly doped high-TC superconductors: A quantum Monte Carlo study

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