Unified theory on angle-resolved photoemission and light absorption spectra of strongly correlated electron systems

Very recently, the angle-resolved photoemission spectrum (ARPES) of [Ni(chxn)(2)Br]Br-2 (chxn = 1R, 2R-cyclohexanediamine), which is a typical one-dimensional Mott insulator, has been experimentally observed. The experiment has strongly suggested that a one-body gap, which is defined as double the ARPES gap, is much smaller than an optical gap given by the light absorption spectrum (LAS). The apparent difference between these two gaps indicates the breakdown of a mean field description of this strongly correlated electron system. In this paper, we show, by using a quantum Monte Carlo method, that the ARPES and LAS of [Ni(chxn)(2)Br]Br-2 are consistently explained within the framework of the one-dimensional extended Hubbard model. It is suggested that the large difference between the one-body and optical gaps is caused by the dynamical Zeeman field induced by the quantum fluctuations.