Spin gap and superconductivity in the ground state of the two-dimensional Hubbard model

Abstract

Recent improvement of quantum Monte Carlo method enables us to study whole range of parameter space of the ground state of the two-dimensional Hubbard model (2DHM). We suggest that there may be the d-wave superconducting ground state (dwGS) in the 2DHM with flat band dispersion around (π,0). We show in the dwGS (1) exponential decay of the real space spin correlation in the (0,1) direction suggestive of opening of the spin gap and (2) coexistence of the resonance peak and the incommensurate peak of magnetic correlation function in the same ground state. At finite temperature, thermal fluctuation washes the superconducting state away in the pure two-dimensional models. When T> T c=0, we observe pseudo gap opening in A( k → ,ω) of the same model. We conclude most experimental results found in high- T c cuprates may be explained qualitatively in terms of the 2DHM with flat band dispersion around (π,0).