Charla Invitada: SANS IN VORTEX MATTER: DYNAMIC REORGANIZATION INTO PARTIALLY DISORDERED VORTEX LATTICES.

G. PASQUINI

Bariloche

Workshop; WORKSHOP ON NEUTRON SCATTERING TO STUDY MAGNETIC, MULTIFERROIC AND SUPERCONDUCTING MATERIALS (WNS2016); 2016

CNEA

In a broad variety of complex systems, an order-disorder transition (ODT) arises as the result of competing interactions. Ordered phases are characterized by correlation functions decaying weakly over distances larger than the relevant system scale whereas, in disordered configurations, correlation lengths ξ are of the same order of magnitude as the mean inter-particle distance a0. Vortex matter in superconductors stand as an ideal playground for the experimental study of these topics: vortex-vortex interactions promote an ordered vortex lattice (VL), while both thermal fluctuations and pinning interactions tend to disorder the system. In materials with very low pinning, such as clean NbSe₂ single crystals, the most of the vortex phase diagram can be described by an ordered dislocation-free Bragg-Glass phase that overcomes an ODT to a disordered phase when increasing the magnetic field and/or the temperature. In this framework, ac susceptibility measurements hinted at the existence of an in-between transitional region[1], in which the VL reorganizes in robust configurations with intermediate degree of disorder, accessible from stationary dynamic states[2]. In this talk I will we present results recently published3, obtained by combining in-situ ac susceptibility measurements with direct SANS imaging of the VL in NbSe2 single crystals, Our findings show a clear connection between the linear ac response, related to the effective vortex pinning, and the bulk spatial correlation of the VL. Configurations with intermediate degree of disorder were obtained by shaking the VL in the proposed transitional region, and remained traceable down to low temperatures. Our results support the existence of the transitional region where, for the first time, a dynamic reordering into robust bulk configurations with intermediate degree of disorder was directly evidenced.[1] G. Pasquini, D. Perez Daroca, C. Chiliotte, L. G. Lozano. and V. Bekeris, Phys Rev Lett 100, 247003 (2008)[2] D. Perez Daroca, G. Pasquini, L. G. Lozano and V. Bekeris, Phys Rev B 84, 012508 (2011)[3 M. Marziali Bermúdez, M. R. Eskildsen, M. Bartkowiak, G. Nagy, V. Bekeris and G. Pasquini, Phys.Rev.Lett. 115, 067001 (2015).