Oral: Oscillatory dynamics in vortex matter near the order-disorder transition

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

Antalya

Conferencia; International Conference of Superconductivity and Magnetism; 2010

Vortex matter in type II superconductors provides a model complex system ideal to explore the behavior of elastic media in the presence of quenched disorder. In this system competing interactions give rise to a complex phase diagram that, in a broad variety of materials, involves an order-disorder (O-D) transition from a quasi-ordered Bragg glass (BG) to a disordered phase with proliferation of topological defects. In the vicinity of this transition, vortex lattice (VL) configurations are generally metastables and display a very complex dynamics that includes memory effects,  dynamical assisted reorganization , aging, etc. In a recent work [1], we have explored the  VL configuration (VLC) landscape in NbSe2 single crystals. By applying a shaking ac field of moderate amplitude before measurment,   we were able to access stationary configuration that are independent of the initial VLC, at each temperature (field). We have  found a transition region between the ordered and disordered phases, where stationary VLCs have an  intermediate degree of disorder that increases with temperature. In the present work we go into 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.. Surprisingly, in the intermediate region, at fixed temperature and field, the VLCs reached after shaking  are independent of the initial conditions but are  frequency dependent. On the other hand, numerical simulations of molecular  dynamics qualitatively reproduce the experimental results, including   the independence of the initial conditions,  and allow us to propose a  consistent picture.