  Engineering effective electronic parameters is a major focus in condensed
matter physics. Their dynamical modulation opens the possibility of creating
and controlling physical properties in systems driven out of equilibrium. In
this work, we demonstrate that the Hubbard $U$, the on-site Coulomb repulsion
in strongly correlated materials, can be modified on femtosecond time scales by
a strong nonresonant laser excitation in the prototypical charge transfer
insulator NiO. Using our recently developed time-dependent density functional
theory plus self-consistent $U$ (TDDFT+U) method, we demonstrate the importance
of a dynamically modulated $U$ in the description of the high-harmonic
generation of NiO. Our study opens the door to novel ways of modifying
effective interactions in strongly correlated materials via laser driving,
which may lead to new control paradigms for field-induced phase transitions and
perhaps laser-induced Mott insulation in charge-transfer materials.
