PLANAR TUNNEL JUNCTION STUDIES OF QUASI-PARTICLE BOUND-STATES IN VORTICES IN ULTRATHIN FILMS

The application of a magnetic field perpendicular to the plane of a ty pe-II superconducting film leads to the formation of vortices in it. W e have made a series of tunneling measurements on quench condensed ult rathin films to investigate the influence of film structure on how the tunneling density of states is affected by magnetic field. We find th at films with microscopically homogeneous structure show clear evidenc e of quasiparticle states bound to vortices. In contrast, granular fil ms with high normal state sheet resistances exhibit no bound states as sociated with the vortices. However, by reducing the sheet resistance of the granular films and thereby enhancing the intergrain coupling, b ound states appear.