Frustration phenomena in Josephson junction arrays on a dice lattice

Abstract 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, 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.