  AC magnetoimpedance measurements performed on proximity-effect coupled
Josephson junction arrays on a dice lattice reveal unconventional behaviour
resulting from the interplay between the frustration f created by the applied
magnetic field and the particular geometry of the system. While the inverse
magnetoinductance exhibits prominent peaks at f=1/3 and at f=1/6 (and weaker
structures at f=1/9,2/9,1/12,...) reflecting vortex states with a high degree
of superconducting phase coherence, the deep minimum at f=1/2 points to a state
in which the phase coherence is strongly suppressed. These observations are
discussed at the light of recent theoretical work in which the concept of
accidental degeneracy plays a central role.
