  We propose a novel possibility of dynamically changing the pairing of
superconductors from $s$ wave to $\eta$ pairing (where the pairs condense at
the Brillouin-zone corner momenta) by driving the system with ac fields. We
consider a periodically-driven attractive Hubbard model in the strong-coupling
regime, and show that the pair-hopping and pair-repulsion terms in the
effective Hamiltonian in the Floquet formalism are drastically renormalized in
different manners between the two terms, which can change the ground states
from an $s$-wave superconductivity to an $\eta$-pairing superconductivity or a
charge-ordered phase. While in isolated systems such as cold atoms a simple
quench scheme would not realize the dynamical phase transition into $\eta$
pairing, we show that there are pathways that realize the dynamical transition,
where the field amplitude is varied via a charge-ordered phase as an
intermediate state.
