1 Universidad de Buenos Aires and IFIBA-CONICET, Buenos Aires, Argentina

2 University of Notre Dame, Indiana, United States of America.

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 present results of a recent experiment in which, by combining in-situ ac susceptibility measurements with direct SANS imaging of the VL in NbSe2 single crystals, we were able to mold and identify VL configurations with intermediate degrees of disorder. This observation is the first direct evidence of oscillatory dynamic reorganization in vortex matter.

[1] G Pasquini et al., Phys Rev Lett 100, 247003 (2008)

[2] D Pérez Daroca et al., Phys Rev B 84, 012508 (2011)

Contact : dubouloz@ill.fr