Investigation of symmetry-breaking flux-line lattice phases in superconductors by small-angle neutron scattering

In single-crystal superconductors in the mixed state, flux-line structures may have a lower symmetry than the host crystal. In this case, multiple degenerate flux lattice domains may be present simultaneously and give rise to complicated small-angle diffraction patterns. The interpretation of these patterns in terms of the flux lattice structure in a single domain is discussed, with particular reference to recently reported spontaneous symmetry-breaking flux-line lattice phases in niobium.