Flux Avalanches in Multi-layer Superconducting Strip Arrays

We have fabricated three-dimensional double- and triple-layer strip arrays of Nb and observed flux penetration into these strip arrays with an applied field perpendicular to the plane by using the magneto-optical imaging method. In the triple-layer strip arrays with large overlaps between the strips, we observed flux avalanches and one-dimensional penetrations perpendicular to the strip similar to the case of double-layer strip arrays. In thicker triple-layer samples, we also observed flux avalanches parallel to the strip. Enhanced demagnetization effect, thermal conductivity between the neighboring layers, and the driving force parallel to the strip are believed to cause these avalanches.