Nonlinear $I-V$ characteristics have been observed in insulating quench-condensed films which are locally superconducting. We suggest an interpretation in terms of the enhancement of conduction by the depinning of a Cooper pair charge density wave, Cooper pair crystal, or Cooper pair glass that may characterize this insulating regime. We propose that this is a more likely description than the Coulomb blockade or charge-anticharge unbinding phenomena.

• Received 24 June 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.037004