Mott Transitions and d-Wave Superconductivity in Half-Filled-Band Hubbard Model on Square Lattice with Geometric Frustration(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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Mechanisms of Mott transitions and d_<x^2-y^2>-wave superconductivity (SC) are studied in the half-filled-band Hubbard model on square lattices with a diagonal hopping term (t'), using an optimization (or correlated) variational Monte Carlo method. In the trial wave functions, a doublon-holon binding effect is introduced in addition to the onsite Gutzwiller projection. We mainly treat a d-wave singlet state and a projected Fermi sea. In both wave functions, first-order Mott transitions without direct relevance to magnetic orders occur at U=U_c, which is approximately the bandwidth, for arbitrary t'/t. These transitions originate in the binding or unbinding of a doublon to a holon. d-wave SC appears in a narrow range immediately below U_c. The robust d-wave superconducting correlation is necessarily accompanied by enhanced antiferromagnetic correlation; the strength of SC decreases, as t'/t increases.
社団法人日本物理学会の論文
2006-11-15