MEISSNER HOLES IN SUPERCONDUCTORS

Features of the magnetic induction patterns at the boundary between op positely magnetized parts in YBCO crystals are studied using an advanc ed magneto-optical technique. Vortices of opposite polarities are reve aled to concentrate at the remagnetization front, equivalent to a loca l increase of the current along it. A model is suggested considering t he presence at the front of a flux-free cylinder formed by closed vort ex loops. Inside the cylinder the loops collapse because their line te nsion exceeds the pinning force. Currents along the cylinder surface a nd in its nearest environment can be large and determine observed flux patterns. A role of the Meissner holes in the appearance of macroturb ulent flux instabilities is discussed.