Competition between superconductivity and SDW in the 2D Hubbard model and possibility of superconductivity along a stripe

The variational Monte Carlo calculation gives a finite bulk-limit value of superconducting (SC) condensation energy in the titled model with next-nearest-site transfer energy t ' in an appropriate parameter region. The obtained SC condensation energy around the optimal doping is of the same order as the experimental value of about 0.26 meV/site for YBCO. This assures the appropriateness of the 2D Hubbard model For cuprate high-T-c superconductors. However, the SDW condensation energy computed by the same method was found to overwhelm the former in the most parameter region where the superconductivity is expected to appear. The SC parameter region seems to be restricted to the highly hole-doped region around the SDW region in a narrow parameter window if it exists. This makes a conspicuous contrast to the experimentally observed wide SC region extending down into the low hole-doping region. We look for the possibility of an inhomogeneous superconducting state coexisting with striped SDW in this low hole-doping SC region. In such a striped SDW state we have obtained an indication that superconductivity is brought about along the stripe in a mid-gap band presumably due to the two-band effect.