Flux penetration into three-dimensional superconducting strip array

•Flux penetrations into double-layer superconducting strip arrays of Nb are observed.•Flux avalanches are observed up to temperatures close to Tc.•When the gap between strips is small, linear flux avalanches perpendicular to the strip arrays are observed.•Enhanced demagnetization effect and thermal conductivity between the strips cause these phenomena.

We have fabricated three-dimensional double-layer strip arrays of Nb and observed flux penetrations into these strip arrays with applied field perpendicular to the plane by using the magneto-optical imaging method. In strip arrays with large overlaps between strips we observed flux avalanches even at 1.5 K below the critical temperature. Novel flux avalanches showed up as one-dimensional penetrations perpendicular to the strip arrays in samples with the maximum overlap. Enhanced demagnetization effect and thermal conductivity between the top and bottom layers are believed to cause these avalanches.