Superconducting heterostructures: from antipinning to pinning potentials

S J CARREIRA ; C CHILIOTTE; V BEKERIS; Y J ROSEN; C MONTON ; IVAN K SCHULLER

SUPERCONDUCTOR SCIENCE AND TECHNOLOGY

IOP PUBLISHING LTD

Lugar: Londres; Año: 2014 vol. 27 p. 85007 - 85012

0953-2048

We study vortex lattice dynamics in a heterostructure that combines two type-II superconductors: a niobium film and a dense triangular array of submicrometric vanadium (V) pillars. Magnetic ac susceptibility measurements reveal a sudden increase in ac penetration, related to an increase in vortex mobility above a magnetic field, H* (T), that decreases linearly with temperature. Additionally, temperature independent matching effects that occur when the number of vortices in the sample is an integer of the number of V pillars, strongly reduce vortex mobility, and were observed for the first and second matching fields, H1 and H2. 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 H* (T), superconducting V pillars repel vortices, and the array becomes an ?antipinning? landscape that is more effective in reducing vortex mobility than the ?pinning? landscape of the normal V sites above H* (T). Matching effects are observed both below and above H* (T), implying the presence of ordered vortex configurations for ?antipinning? or ?pinning? arrays.