We have studied the ground state of the two-dimensional Hubbard model by using the adaptive sampling quantum monte carlo method. We found enhancement of the d-wave correlation function, the spin gap and the coexistence of both the commensurate and incommensurate peaks in $S(\vec{ q})$, 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.
Categories: cond-mat.str-el cond-mat.supr-con