Kosterlitz-Thouless transition of fluxless solitons in superconducting YBa2Cu3O/sub 7-//sub δ/ single crystals

We present detailed evidence for a resistive Kosterlitz-Thouless transition in YBa2Cu3O/sub 7-//sub δ/ single crystals. The Kosterlitz-Thouless temperature T/sub KT/ is the onset temperature for zero-resistance superconductivity in the ab planes; three-dimensional superconductivity throughout the sample follows at a lower temperature. The objects which engage in the transition do not carry flux --they are not the flux vortices of conventional theory. They are more likely normal-state excitations that pair up at T/sub KT/ to form quasi-two-dimensional superconducting condensates