  We theoretically investigate correlated electron dynamics in high-harmonic
generation (HHG), using all-electron \emph{ab initio} simulations for
three-dimensional real alkali-metal atoms. The resulting harmonic spectra
exhibit a plateau extended beyond the usual cutoff and a prominent resonance
peak above the plateau. These remarkable features arise from the cation
response dramatically enhanced by laser-induced electron recollision, which is
a key process of attosecond science. This demonstrates that high-harmonic
spectroscopy provides new possibilities to explore dynamical electron
correlation in strong laser pulses.
