Sy. Hsu et Jm. Valles, TUNNELING STUDIES OF VORTICES IN HIGH-SHEET-RESISTANCE GRANULAR SUPERCONDUCTING FILMS, Physical review. B, Condensed matter, 49(9), 1994, pp. 6416-6419
We have measured the tunneling density of states in ultrathin high-she
et-resistance, 16 OMEGA < RN < 17 kOMEGA, granular Pb films in perpend
icular magnetic fields, H. At the lowest R(N), states appear within th
e superconducting energy gap at low fields (H < 0.1 T) indicating the
presence of vortex cores. At the highest R(N), no states appear in the
gap in fields as high as 2 T indicating that the field-induced vortic
es do not have cores. A simple model implies that the average Josephso
n coupling energy between the grains of the film is comparable to the
condensation energy of a single grain at the R(N) separating these two
regimes.