Small Angle Neutron Scattering Experiments on Vortices in Copper Oxide Superconductors

Abstract

When the concept of magnetic flux lines in superconductors was first proposed by Abrikosov, it was sufficiently revolutionary to require microscopic experimental confirmation. This was eventually supplied by the pioneering experiment of Cribier et al. [1], which showed that flux lines could be detected by their ability to scatter neutrons. This resulted in many detailed investigations, using SANS and other techniques, of the structure of flux lines in superconductors. This was essentially a “crystallography” of the flux line lattice (FLL) that forms inside a Type-II superconductor when the applied magnetic field H is sufficient to cause vortices to enter (>H c1) but insufficient to destroy superconductivity altogether (<H c2). The SANS technique was re-invigorated by the discovery of High-Tc Superconductors, which are all Type-II, and the subsequent neutron observations of flux lines in YBCO [2]. Since then, the interest has spread to flux structures in other materials such as Heavy Fermion [3] and Borocarbide superconductors [4,5], as well as the direct observation of Flux Lattice Melting in High-Tc materials [6,7]. In this article, we shall review the fundamentals of the SANS technique applied to the observation of flux lines, the nature of flux structures that one would expect to observe, and recent results in High-Tc materials. We shall conclude with an indication of future possibilities for this and related techniques.