Nonlocal electrodynamics of Josephson junctions in thin films and fractional vortices

• Published in: Superconductor science & technology 2002-03, Vol.15 (3), p.307-314, Article 307
• Main Authors: Mints, R G, Papiashvili, Ilya
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Multilayers, superlattices , heterostructures; Physics; Proximity effects, weak links, tunneling phenomena, and Josephson effects; Proximity effects, weak links, tunneling phenomena, and josephson effects, adreev effect, sn and sns junctions; Superconducting films and low-dimensional structures; Superconductivity
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/0953-2048/15/3/304

The phase difference across a Josephson junction is considered for a film with a thickness d mu chlt l, where l is the London penetration depth in the superconducting banks. Attention is given to the case of a Jc varying along the junction. Nonlinear integro-differential equation determines the spatial distribution of phase difference for d mu chlt l. Josephson properties of grain boundaries in thin-YBCO films are treated for the case of jc alternating along these boundaries. If the typical amplitude of alternations of jc is high compared to the average value of jc, then a spontaneous flux and two types of fractional Josephson vortices can be observed. The fractional Josephson vortices keep magnetic fluxes f1 and f2, where f1 + f2 = f0, f0 is flux quantum, and f1 < f0/2, f2 > f0/2. Authors demonstrate that these fractional vortices can be observed in thin-YBCO films under conditions of appearance of the spontaneous magnetic flux. A method is proposed to extract the fractional vortices from the experimental flux patterns. Propagation of an electromagnetic wave along a grain boundary with an alternating Jc is treated as an example of an application of the integro-differential equation for the phase difference. 36 refs.