  High-harmonic generation (HHG) in crystalline solids have been examined so
far on the basis of one-body energy-band structures arising from electron
itineracy in a periodic potential. Here, we show emergence of HHG signals which
are attributed to dynamics of many-body states in a low-dimensional correlated
electron system. An interacting fermion model and its effective pseudo-spin
model on a one-dimensional dimer-type lattice are analyzed. Observed HHG
signals in a spontaneously symmetry-broken state, where charge densities are
polarized inside of dimer units, show threshold behavior with respect to light
amplitude and are interpreted in terms of tunneling and recombination of
kink-antikink excitations in an electric field.
