Observation of domain-wall superlattice states in a frustrated triangular array of Josephson junctions

A family of ground states at frustrations f=1/2-(1/2)${\mathit{N}}^{\mathrm{-}1}$, with N an integer ≥2, has been observed in the superfluid response of a triangular Josephson junction array as a function of the magnetic flux (∝f) threading a unit cell. These states can be constructed by introducing one- or two-dimensional superlattices of domain walls on the background of the checkerboard ground state at f=1/2, the 1D superlattice (striped phase) being energetically more favorable for N>3. A structural change of the ground state from the striped phase to a 2D superlattice of vacancies is predicted at ${\mathit{f}}_{\mathit{c}}$≊0.468.