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

Abstract

Local-magnetic-field distributions in the superconducting mixed state of high-${\mathit{T}}_{\mathit{c}}$ cuprates were measured by muon-spin rotation (μSR) in the absence of applied driving forces. In this first analytical treatment, a critical-state model, incorporating an anisotropic penetration depth [${\lambda }_{\mathit{a}\mathit{b}}$(0)=1300±100 Å in the basal plane], reveals the strong influence of local pinning on the characteristic shape of low-temperature μSR Fourier spectra for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. The linewidths are found to be nearly independent of flux density, indicative of noncollective or local pinning.