Superconducting heterostructures: examples of attractive and repulsive periodic pinning arrays

VICTORIA BEKERIS

madrid

Workshop; Vortex 2015; 2015

Universidad Autónoma de Madrid

Superconducting heterostructures: examples of attractive and repulsive periodic pinning arrays Victoria BEKERIS Universidad de Buenos Aires, FCEyN, Departamento de Física and IFIBA, CONICET, Argentina. We studied vortex lattice dynamics in ac susceptibility experiments in two heterostructures. The first one combines two type-II superconductors: a niobium film and a dense triangular array of submicrometric vanadium (V) pillars [1]. The second structure is a superconducting film grown on top of a two-fold symmetry array of submicrometric magnetic dots [2]. In the first case, a sudden increase in ac penetration, above a magnetic field, H*(T), that decreases linearly with temperature, reveals a sudden decrease in pinning. Additionally, temperature independent matching effects, for one or two vortices per primitive cell, at H1 and H2 are observed. The angular dependence of H1, H2 and H*(T) shows that matching is determined by the normal applied field component, while H*(T) is independent of the applied field orientation. This important result identifies H*(T) with the critical field boundary for the normal to superconducting transition of V pillars. Below (above) H*(T), superconducting V pillars repel (attract) vortices, and matching effects are observed in both cases implying the presence of ordered vortex configurations for ?anti-pinning? or ?pinning? arrays. In the second studied heterostructure the induced ac currents flow parallel to the short and to the long side of the pinning array in different areas of the samples simultaneously. This behavior produces remarkable effects in the vortex lattice dynamics. Competing unstable vortex configurations seem to lead to an increase in vortex mobility precluding the reconfiguration transition, earlier reported in transport experiments. At high temperatures, the magnetic permeability of the dots is the mechanism that governs JC, while a crossover to pinning by interstitial point defects is observed as the temperature is reduced. References [1] S. J. Carreira, C. Chiliotte, V. Bekeris, Y. J. Rosen, C. Monton and Ivan K. Schuller, Supercond. Sci. Technol. 27 085007 (2014). [2] A. J. Moreno, C. Chiliotte, G. Pasquini, V. Bekeris, A. Gomez, J. del Valle, E. M. Gonzalez, J. L. Prieto and J. L. Vicent, Supercond. Sci. Technol. 28 015001 (2015). E-mail: (vbekeris@df.uba.ar)