Invitada: AC dynamics and vortex matter reorganization near the order-disorder transition

G. PASQUINI; D. PÉREZ DAROCA; G. LOZANO; V. BEKERIS

Recife

Workshop; VIII Brazilian School of Superconductivity and Workshop in Frontiers on Superconductivity and Magnetism; 2010

Among the broad and complex phenomenology observed in vortex matter one of the most surprising behavior occurs in the neighborhood of the order-disorder (O-D) transition, where the system evolves from a quasi-ordered Bragg glass (BG) to a disordered phase with proliferation of topological defects. Metastability,  history effects and a very complex dynamics are common facts observed in this region both in low and in high Tc materials. An enlarged crossing phase boundary between the ordered and disordered phases has been reported and corroborated for our group [1] by using non invasive ac susceptibility measurements in the linear regime.  We have shown that in this transition region a shaking AC field can even order or disorder the VL, driving the system to final vortex lattice configuration (VLCs) with an intermediate degree of disorder that are independent of the initial conditions at each temperature (and field). In the present work we go deeper into the nature of these stationary configurations, by studying the physics underlying the effect of the shaking field. By means of linear ac susceptibility experiments in the Campbell regime (that exclude current induced vortex lattice reorganization), we explore the VLC landscape reached by varying the frequency and waveform of the shaking field throughout the O-D transition. We show that, in the intermediate region, the VLCs reached after shaking are independent of the initial conditions but can depend on the shaking protocol. On the other hand, by means of numerical simulations of molecular dynamics we have performed a comprehensive description [2] of the different dynamic regimes of a VL driven by AC forces in the presence of random pinning. A careful numerical calculation has been performed in order to establish the relationship between the ac shaking field and the resulting ac driving force.     Our experiments are consistent with our numerical predictions, and show experimental evidence of AC driven vortex lattice self organization. [1] G. Pasquini, D. Pérez Daroca, C. Chiliotte, G. Lozano and V. Bekeris; Phy. Rev. Lett. 100, 247003 (2008).