One-body green functions of half-filled Hubbard models: Predominance of multimagnon incoherent component and minuteness of zeromagnon coherent one

One-body Green functions of one- and two-dimensional half-filled Hubbard mo dels are calculated by means of a quantum Monte Carlo method. To distinguis h a zeromagnon coherent component from a multimagnon incoherent one in the Lehmann spectrum of the one-body Green function, a site-diagonal staggered potential Delta is artificially added to the Hubbard model. Due to this a, the energy gap opens in the magnon excitation and the zeromagnon coherent c omponent is well separated from the multimagnon incoherent one. Systematic analysis on the h-dependence of the coherent and incoherent components clea rly shows that the Lehmann spectrum of the one-body Green function is predo minated by the incoherent component and the coherent component makes only a minute contribution to the spectrum. Our results indicate that a peak in t he angle-resolved photoemission spectrum of the so-called Mott-Hubbard insu lator does not correspond to a one-body state. (C) 2001 Elsevier Science B. V. All rights reserved.