  Many-electron dynamics induced by a symmetric monocycle electric-field pulse
of large amplitude is theoretically investigated in one- and two-dimensional
half-filled extended Hubbard models on regular lattices (i.e., without
dimerization) using the exact diagonalization method for small systems and the
Hartree-Fock approximation for large systems. The formation of a
negative-temperature state and the change from repulsive interactions to
effective attractive interactions are shown to be realized for a wide region of
the field amplitude and the excitation energy. For a nonnegligible intersite
repulsive interaction, the numerical results are consistent with the fact that
the phase separation between charge-rich and charge-poor regions is caused by
the corresponding effective attraction.
