Transport properties of ybco thin films near the critical state with no applied field

TL;DR

This study investigates the transport properties of YBCO thin films near the critical state, showing that twin boundaries act as rows of Josephson weak links whose characteristics depend on temperature, film thickness, and substrate effects.

Contribution

It provides a new model linking twin boundary weak links to transport behavior, with a universal function for weak link length as a function of temperature.

Findings

Weak links form superimposed rows along twin boundaries.

Critical surface current density depends on temperature and weak link structure.

Substrate and growth technique significantly influence weak link properties.

Abstract

Transport measurements carried out on twinned ybco films are compared to the predictions of a previously proposed model suggesting that the vortices move along the films twin boundaries that behave as rows of Josephson weak links [P.Bernstein and J.F.Hamet, J.Appl.Phys.95 (2004) 2569]. The obtained results suggest that, except if the films are very thin, the twin boundaries consist of superimposed rows of weak links with mean height,ds, whose mean length along the TBs is an universal function of T/Tc, the reduced temperature. This conclusion yields a general expression for the critical surface current density of the films as a function of T/Tc and of the number of superimposed weak links rows, while the critical current density depends on ds. A comparison of the measurements reported by various authors shows that the nature of the substrate and the growth technique have both a strong effect on ds . The existence of superimposed weak links rows is attributed to extended defects generated by y2o3 inclusions.