Superfluid Density in Ultrathin YBCO Films

ABSTRACTWe studied the transition of 8 nm-thick YBCO films deposited with and without YBaCuNbO buffer from the superconducting to resistive state due to the temperature or transport current increase. For both film types, the current –voltage characteristics and resistive transition followed the Kosterlitz-Thouless transition model. The superfluid densities were found from the Kosterlitz-Thouless transition temperature TKT to be about 3% and 1.3% of the total carrier density in YBCO with and without buffer, respectively. We believe that the low superfluid densities indicate the presence of weak links in the film.