Vortex lattice disorder in YBa2Cu3O7-δYBa2Cu3O7-δ studied with ββ-NMR

In this paper, we report Li+8ββ-NMR measurements in thin Ag films deposited on the surface of YBa2Cu3O7-δYBa2Cu3O7-δ (YBCO) in the vortex state. The resonance in the Ag overlayer broadens dramatically below the superconducting transition temperature TcTc, as expected from the underlying vortex lattice in the YBCO. However, the lineshape is much broader and more symmetric than expected for an ideal vortex lattice. These results indicate the observed field distribution in the Ag overlayer is dominated by extrinsic, long length scale disorder.