Observation of current strings in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals

A flux step between regions of magnetic flux of opposite polarities in the remanent state of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals is observed by means of a high resolution magneto-optical technique. This step indicates a current string inside the crystal platelet which is similar to the string appearing in the solution of the critical state problem for a cylindrical type-II superconducting wire with transport current if one takes into account the finite lower critical field {ital H}{sub {ital c}1}. The conditions for the existence of the current string and its properties are discussed.