Abstract
Coexistence of and competition between antiferromagnetism (AF) and d-wave superconductivity (SC) are studied for a Hubbard model on the square lattice with a diagonal transfer t ′ , using a variational Monte Carlo method. The following improvements are introduced into the trial function: (1) Coexistence of AF and d-wave singlet gaps that allows a continuous description of their interplay, (2) band renormalization effect, and (3) refined doublon–holon correlation factors. Optimizing this function for a strongly correlated value of U / t , we construct a phase diagram in the δ (doping rate)- t ′ / t space, and find that for t ′ / t ⩾ - 0.15 a coexisting state is realized, whose range of δ extends as t ′ / t increases. In contrast, for t ′ / t = - 0.3 , AF and SC states are mutually exclusive, and a coexisting state does not appear. In connection with the “two-gap” problem, we confirm even for the present refined function that the gradient of momentum distribution function at the antinodal point mainly dominates the magnitude of the d-wave SC correlation function.
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