DIMPLES DUE TO DISLOCATIONS AT THE SUPERFLUID SOLID INTERFACE OF HE-4/

On vicinal planes the surface stiffness is quite anisotropic and a cry stal defect, terminating at the interface, is predicted to produce a 1 0...50 nm deep dimple with macroscopic lateral extent (up to a few mm) . We have searched for such depressions using high resolution interfer ometry. Some times our measured interferograms of the superfluid/solid interface display unexpectedly large dimples. The volume and shape of the observed objects suggest that these dimples are caused by bundles of about 10 dislocations.