https://doi.org/10.1140/epjb/e2005-00163-x
Surface-barrier effects in the microwave second-harmonic response of superconductors in the mixed state
1
INFM and Dipartimento di Scienze Fisiche ed Astronomiche,
Universita di Palermo, Via Archirafi 36, 90123 Palermo, Italy
2
EDISON S.p.A. - Divisione Ricerca e Sviluppo, Via U. Bassi 2, 20159 Milano, Italy
Corresponding author: a livigni@fisica.unipa.it
Received:
11
November
2004
Revised:
25
February
2005
Published online:
16
June
2005
We report on transient effects in the microwave second-harmonic response of different type of superconductors in the mixed state. The samples have contemporarily been exposed to a dc magnetic field, varying with a constant rate of 60 Oe/s, and a pulsed microwave magnetic field. The time evolution of the signal radiated at the second-harmonic frequency of the driving field has been measured for about 500 s from the instant in which the dc-field sweep has been stopped, with sampling time of ~0.3 s. We show that the second-harmonic signal exhibits two relaxation regimes; an initial exponential decay, which endures roughly 10 s, and a logarithmic decay in the time scale of minutes. Evidence is given that the decay in the time scale of minutes is ruled by magnetic relaxation over the surface barrier.
PACS: 74.25.Ha – Magnetic properties / 74.25.Nf – Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.) / 74.60.Ge – Flux pinning, flux creep, and flux-line lattice dynamics
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2005