Flux-Line Arrangement in Superconductors as Revealed by Direct Observation

Abstract

The flux‐line lattice in a type‐II superconductor in the remanent state is investigated by means of a decoration method. The triangular lattice contains various kinds of defects, the most important of which are flux‐line dislocations. A critical lattice parameter d_c exists such that for lattice parameters d>d_c the flux lines form no longer a lattice but a ``flux‐line fluid.'' A belt directly underneath the specimen surface is free from flux lines. The transition from the ``fluid'' to the flux‐free region has been utilized to estimate in a fairly direct way the pinning forces acting on the flux lines.