All the superconducting action takes place in planes of copper and oxygen atoms sandwiched between layers of other elements, such as yttrium and barium. In the case of YBCO, excess oxygen in the yttrium barium oxide bread soaks up electrons from the copper oxide meat, leaving behind holes, which can be thought of as positively charged particles. Such condensate fluids flow en masse without friction. Conventional superconductors involve condensates of electron pairs held together by a well-understood interaction, but no one knows what pairs up the holes in cuprate superconductors. Individual holes introduced to this rigid arrangement cannot move about easily, because the motion would disrupt the chessboard arrangement.
Holes can move readily along such stripes without upsetting the chessboard pattern elsewhere.
Stripes fixed in place cannot produce superconducting pairs of holes, but dynamic stripes, which meander across the chessboard, can. Such meandering stripes should also slightly displace atoms in the cuprate planes. Thirumalai Venkatesan of the University of Maryland and his co-workers fired helium ions through the channels formed by the rows of atoms in crystal planes and saw evidence of these displacements. As the crystal was cooled, the effect varied as expected if stripes form above superconducting temperatures and generate the required pairing of holes at lower temperatures. Herbert A. Mook of Oak Ridge National Laboratory and his colleagues found direct evidence for meandering stripes as well.