Evidence for nonconventional vortex dynamics in an ideal two-dimensional superconductor

Impedance measurements performed on a weakly frustrated triangular array of Josephson junctions over a wide range of frequencies and at temperatures such that vortex pinning is irrelevant reveal that vortex dynamics in an ideal two-dimensional (2D) superconductor does not obey Drude's classical prediction for a 2D Coulomb gas of free and independent vortex charges. An analysis in terms of a complex vortex dielectric constant implies that the vortex mobility vanishes logarithmically in the limit of small frequencies, thereby pointing to anomalous vortex diffusion.