VORTEX CORRELATION LENGTHS AND BUNDLE SIZES FROM VOLTAGE NOISE IN YBA2CU3O7

Voltage noise is one way to estimate flux-bundle sizes in superconduct ors undergoing Aux creep. Modeling such data from epitaxial films of Y Ba2CU3O7. we show that at high temperatures, the bundle size grows wit h the c-axis correlation length of pancake vortices (residing in the C u-O planes), while at low temperatures, flux creep is consistent with vortex-line bundles which are larger than a minimum size. The separati on of these regimes is roughly at the vortex-lattice melting line, imp lying that a large c-axis correlation length is needed for vortex-latt ice freezing.