Small-angle neutron scattering and magnetic decoration: complementary techniques applied to reveal structural properties of vortex matter

YANINA FASANO

Bariloche

Conferencia; Invited talk en Workshop on Neutron Scattering to Study magnetic, multiferroic and superconducting materials; 2016

CNEA Lab haces neutrones y Paul Scherrer Institut de Suiza

Understanding in detail the structural properties of the vortex phases nucleated in superconductors remains an important open question in soft condensed matter. This is partly due to the difficulty in getting a complete picture since the available experimental techniques that are sensitive to different directions (longitudinal and transversal) are applicable generally in dissimilar field ranges and provide information on either surface or volume properties. In addition, since most of the vortex phases are glasses due to the disorder introduced by the pinning potential, field-cooling experiments provide information only on a state quenched at a given temperature during the cooling process. Here we discuss the combination of Bitter magnetic decoration and small-angle neutron scattering (SANS) techniques, providing information on the real and reciprocal space structural properties, to study the longitudinal and transversal order characteristic of vortex matter. Magnetic decoration allows imaging of the distribution of individual vortices in the ab plane (transversal direction) but on the surface of the sample; SANS provides volumetric reciprocal-space information on the ab plane and along the c-axis (longitudinal direction). However, magnetic decoration achieves single-vortex resolution only at low fields whereas SANS is usually applied at high fields. We present data in the high-temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_8$ applying both techniques at an intermediate field of 100 Gauss. In particular, we discuss the transversal and longitudinal structural properties of the glassy low-field solid vortex phase quenched in field-cooling experiments and the effect of a dithering field that would drive the system to the equilibrium state at the measuring temperature.* work done in collaboration with Alain Pautrat from Ensicaen, Caen, France, Charles Simon and Charles Dewhurst from Institut von Laue-Langevin, Grenoble, France.