Two-step superconducting-to-normal transitions in frustrated triangular Josephson-junction arrays

Abstract

Current–voltage characteristics measurements suggest that the superconducting-to-normal transition in triangular Josephson-junction arrays with the frustration index f=1/4 and 1/3, which may have excitations of zero-energy domain walls, occurs in two steps, a vortex-disordering transition followed by a Berezinskii–Kosterlitz–Thouless-like phase-disordering transition at a higher temperature. The transport data also indicate that a similar two-step transition occurs in a weakly frustrated array as well. Experimental findings for a weakly frustrated array are inconsistent with existing theory.