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 N-1, with N an integer greater-than-or-equal-to 2, has been observed in the superflu id response of a triangular Josephson junction array as a function of the magnetic flux (is-proportional-to f) threading a unit cell. These states can be constructed by introducing one- or two-dimensional super lattices of domain walls on the background of the checkerboard ground state at f = 1/2, the 1D superlattice (striped phase) being energetica lly 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 f(c) almost-equal-to 0.468.