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Mechanisms of Mott transitions and d x 2 y 2 -wave superconductivity (SC) are studied in the half-filledband Hubbard model on square lattices with a diagonal hopping term (t 0 ), 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 0 =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 0 =t increases.
A Wed, study studied this question.