Dynamic reorganization and thermal history effects in vortex matter

History effects related to plasticity and metastable configurations in the vicinity of an order-disorder transition (ODT) are common features in a variety of systems, among which vortex matter becomes a prototype model. In superconducting materials with randomly distributed weak pinning centers, the stable vortex phase at low temperature and low magnetic fields is an ordered dislocation free Bragg Glass (BG). With increasing field and/or temperature, the system undergoes an ODT to a strongly pinned disordered phase, whose fingerprint is the sudden rise of the effective pinning, known as Peak Effect (PE). Below the PE, a field-cooled vortex lattice (VL) remains trapped in a disordered metastable configuration, but can reach the stable ordered BG with the help of large shaking AC fields. The existence of a transitional region between the ordered and the disordered phases and the origin of thermal and history effects observed in the effective pinning remained controversial issues for more than a decade.
In this talk I will review the results obtained by our group in joint linear ac susceptibility and neutron scattering experiments, supporting the existence of a narrow in-between transitional region where the application of shaking fields gives rise to bulk VL configurations with intermediate degree of dislocation density correlated with intermediate effective pinning [1]. Numerical simulations [2] and very recent experiments suggest that these “intermediate” configurations are originated from a VL reorganization driven by the oscillatory dynamics. In addition, in a recent work [3], we have shown that controversial thermal hysteretic pinning effects are not related with a measurable change in the dislocation density. I will discuss different proposed pictures.

[1] G. Pasquini et al., PRL 100, 247003 (2008); M. Marziali Bermúdez et al., PRL 115, 067001(2015).
[2] D. Perez Daroca et al., PRB 84, 012508 (2011).
[3] M. Marziali Bermúdez et al., PRB 95, 104505 (2017).