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

Angle-resolved photoemission spectrum (ARPES) and light absorption spectrum (LAS) of [Ni(chxn)2Br]Br2 (chxn=1R, 2R-cyclohexanediamine), which is a typical one-dimensional (1D) Mott insulator, are theoretically studied. The experimentally observed spectra have strongly suggested that a one-body gap, defined as double the ARPES gap, is much smaller than an optical gap, given by the LAS. The apparent difference between these two gaps indicates the breakdown of the mean-field description of the strongly correlated electron system. In this paper, by using the quantum Monte Carlo method, we show that the ARPES and LAS of [Ni(chxn)2Br]Br2 are consistently explained within the framework of the 1D extended Hubbard model, and confirm the small one-body gap and large optical gap. We also suggest that the apparent difference in the gap structures is caused by a dynamical Zeeman field induced by quantum fluctuations.