A new scenario, based on crystallization of oppositely charged vortex-antivortex pairs into a 2D ionic crystal, is proposed for the transition in thin superconducting films with high pair density. We also discuss possible melting of this crystal and the emergence of dissipation. This model is also shown to apply to superfluid He films in cases where the energy to create a vortex is reduced due to interaction with the substrate.

• Received 28 December 1992

DOI:https://doi.org/10.1103/PhysRevLett.71.2138