CONICET | Buscador de Institutos y Recursos Humanos

YBCO is a superconductor with a broad field of applications especially since the appearance of second generation coated conductors enabling superconducting power devices. Consequently, there have been a lot of efforts to control vortex pinning and vortex dynamics in this type of material. Natural defects like twin boundaries, stacking faults, dislocations, nanometric secondary phases,... may act as vortex pinning centers, however one would desire to introduce artificial defects in a controlled manner to tune and manipulate the superconducting properties. In this work we study vortex-defect interaction using the Bitter decoration technique for real visualization of the flux line lattice (FLL). Results on YBCO single crystals and films (samples with different intrinsic pinning) have been obtained. We have generated artificial nano-defects using indentations at nano-scale and irradiation with focus ion beam in the same samples. Bitter decoration results demonstrate that when the artificial defects are generated in single crystals (ordered systems), the FLL symmetry is lost and an increase of vortex densityoccurs at the nano-defects. Instead, for the case of thin films (disordered systems), an increase in FLL ordering and symmetry is obtained. Finally, we have derived an energetic model based on London theory as an approximation of the Ginzburg-Landau solution, with a general analytic expression for the energy of arbitrary arrangements of vortex position [1]. This model allows us to estimate values for the pinning energy of the FLL directly from decorated images. We observe that estimated values for the pinning energy increase in agreement with the increase of system disorder and also of the total energy of the FLL. With this model we are able to estimate the pinning energy associated to the different defects introduced and compare them to the pre-existing ones.

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