Depth-resolved profile of the magnetic field beneath the surface of a superconductor with a few nm resolution

The variation of a magnetic field as a function of depth beneath the surfac e of an YBa2Cu3O7-delta thin film in the Meissner state has been measured u sing low energy muons. The depth of implantation was varied from 20-150 nm by tuning the energy of the implanted muons from 3-30 keV. These are direct measurements of the penetration of a magnetic field beneath a superconduct ing surface which illustrate the power of low energy muons for near surface studies in superconductivity and magnetism.