Interplay between antiferromagnetism and superconductivity in two-dimensional Hubbard model

Using a variational Monte Carlo method, we discuss the interplay between antiferromagnetism (AF) and superconductivity (SC) in a Hubbard model on a square lattice with a diagonal transfer t^′. We simultaneously introduce the following improvements 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 in the range of fourth-neighbor hopping, and (3) refined doublon-holon correlation factors. For t^′ / t = - 0.3, appropriate to hole-doped cuprates, it is found that AF ordered state is stabilized near half filling, especially, for U ∼ band width, by retrieving the nesting condition. As the doping rate increases, AF is weakened and a pure d-wave SC phase evolves for large U. The coexisting state of SC and AF orders appears only in a narrow range of U (∼ band width) and electron density n (= 0.8).