  We investigate a new mechanism to create large curvature perturbations on
small scales due to parameter resonance in a single-field inflationary model
with a small periodic structure upon the potential. After reentering the
horizon, the amplified curvature perturbations can lead to observable
primordial black holes as well as stochastic gravitational waves. The mass of
primordial black holes and frequency of the induced gravitational waves depend
on the model parameters. The resulted primordial black hole could constitute
all dark matter or a fraction of dark matter in the universe, and corresponding
stochastic gravitational waves fall in the frequency band measurable for the
pulsar timing array and the space-based gravitational wave detectors.
