Parameter-dependences of superconducting condensation energy of 2D Hubbard model

By calculating the superconducting and spin density wave (SDW) condensation energies for the two-dimensional Hubbard model by the variational Monte Carlo method on the 10 x 10 and 12 x 12 lattices, we have searched for the parameter region where superconductivity overcomes SDW in the ground state. This model leads to a reasonable superconducting region as a function of electron density p when on-site Coulomb energy U = 6 in units of nearest-neighbor transfer energy t which was suggested from recent neutron diffraction data of the spin wave energy. When we fix U = 6 and rho = 0.84 (hole density 0.16), the superconducting phase wins in a relatively narrow range of -0.10 less than or equal to t' less than or equal to 0.05, where t' is the second-neighbor transfer energy. In this region the superconducting condensation energy sharply increases with decreasing t', which is considered to give the basis for clarifying the family dependence of the maximum T-c in the cuprate superconductors. (C) 2003 Elsevier B.V. All rights reserved.