Local magnetic fields in the pinned vortex state: Effect on the -spin-rotation line shape

Local-magnetic-field distributions in the superconducting mixed state of high-Tc cuprates were measured by muon-spin rotation (SR) in the absence of applied driving forces. In this first analytical treatment, a critical-state model, incorporating an anisotropic penetration depth [ab(0)=1300±100 in the basal plane], reveals the strong influence of local pinning on the characteristic shape of low-temperature SR Fourier spectra for YBa2Cu3O7. The linewidths are found to be nearly independent of flux density, indicative of noncollective or local pinning.