  Spin pumping driven by bistable exchange spin waves is demonstrated in a
Pt/Y$_3$Fe$_5$O$_{12}$ film under parametric excitation. In the
Pt/Y$_3$Fe$_5$O$_{12}$ film, the spin pumping driven by parametric excitation
selectively enhances the relaxation of short-wavelength exchange spin waves,
indicating strong coupling between the exchange spin waves and spin currents at
the interface through efficient spin transfer. The parametric spin pumping,
furthermore, allows direct access to nonlinear spin wave dynamics in
combination with the inverse spin Hall effect, revealing unconventional
bistability of the exchange spin waves.
