  We have studied the magnetic field or disorder induced insulating and
metallic phases in amorphous Ta superconducting thin films. The evolution of
the nonlinear transport in the insulating phase exhibits a non-monotonic
behavior as the magnetic field is increased. We suggest that this observation
could be an evidence of the presence of localized Cooper pairs in the
insulating phase. As the metallic phase intervenes the superconducting and
insulating states in Ta films, this result further reveals that Cooper pairs
also exist in the metallic ground state.
