A STUDY OF VORTEX MOVEMENTS PARALLEL AND PERPENDICULAR TO TWIN BOUNDARIES IN YBCO

Twin boundaries constitute a barrier to the free movement of vortices particularly in high temperature superconductors. This phenomenon has been studied in detail with a specially prepared sample of YBCO. The l atter is a heavily twinned single crystal but containing a single doma in i.e. the twin boundaries are parallel throughout the sample. Thus w ith a temperature gradient applied parallel and then perpendicular to the twin boundaries, one obtains remarkable contributions to the Seebe ck and Nernst effects observed as a function of temperature for both m agnetic field polarities. The various aspects of our data are all cons istent, including the observation of a voltage due to the movement of vortices between adjacent pairs of twin boundaries.