Variational Monte Carlo study of pairing symmetry in Sr₂RuO₄

With a mind to superconductivity (SC) arising in Sr₂RuO₄, we study a Hubbard model on square lattice including second-neighbor hopping t′, using an optimization variational Monte Carlo method. As a pairing state, we have chosen d_{x2 - y2} (d) wave for singlet and p_x (p)-wave for triplet pairing state. In the trial wave functions, a doublon-holon binding effect is introduced in addition to the onsite Gutzwiller projection. By calculating condensation energies of the SC states, we found that when t′ = -0.4t, the d-wave state is stabilized against the normal state for 0.6 < n < 1. On the other hand, p-wave state is never stabilized in this regime. Based on this result, it is difficult to understand a spin-triplet state simply from the single-band Hubbard model with onsite Coulomb interaction.