The ground state of the two-dimensional Hubbard model

We have studied the ground state of the two-dimensional Hubbard model by using the recently proposed adaptive sampling quantum monte carlo (ASQMC) method. We have paid attention to the model whose non-interacting band dispersion is almost flat near ( π, 0) . To minimize the effect of the finite size gap overlying the Fermi level, we have tuned both filling and band structure. We found enhancement of the d-wave correlation function at large distance, the spin gap and the momentum distribution function consistent with the d-wave gap. We also found the coexistence of both the commensurate and incommensurate peaks in S( q) , which does not contradict a recent experimental finding that both the resonance peak and the incommensurate peaks reside in the same doping level of YBCO and BSCCO.