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.
- Hubbard model
- Variational Monte Carlo method
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering