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Transport measurements on YBa2Cu3Oyhave revealed strong history dependences in pinning properties of the vortex solid. By using an annealing current to control exposure of the vortex system to the disorder potential, we were able to study the development of such hysteretic responses, across the region of the vortex freezing transition. We have explained the observed behaviour in terms of coexistent vortex liquid and solid phases.

Magnetotransport measurements on a clean, untwinned YBa2Cu3O7-d single crystal show that the vortex dynamics at temperatures just below the vortex lattice melting transition are highly dependent on the type of modulation of the probing current. While in the case of DC current the flux flow is disordered, the “shaking” of the vortex lattice by a square-wave current leads to a more uniform vortex motion. A small asymmetry (~10%) in the durations of the positive and negative parts of the square-wave period induces periodical oscillations of the voltage response amplitude. The period of oscillations (~100 s) is the same order of magnitude as the time needed for vortices to cross the sample (transit time). We relate the observed voltage oscillations to a periodically ordered vortex motion.

Pinning by point-like defects and twin boundaries in single-crystalline YBa2Cu3O7-d has been investigated by measuring resistance and current-voltage characteristics in fields up to 5 T. A number of untwinned and twinned samples with different densities of point-like defects were studied. The experimental results are compared within the framework of vortex-entanglement.