Direct observation of a flux line lattice field distribution across an YBa2Cu3O7-delta surface by low energy muons

The technique of low energy muon spin rotation has been used to measure the microscopic field distribution in the vortex state of a 700 nm thick YBa2C u3O7-delta film. By varying the implantation energy of the muons we were ab le to monitor the spatial evolution of the magnetic field distribution as t he Bur lines emerge through the surface of the superconducting film. The re sults are in excellent agreement with calculations based on the London mode l and clearly demonstrate the potential of the new technique for thin film and surface studies.