Ion Beam Thinning of YBa₂cu₃o₇ Films: Approach to a Limiting Thickness for Superconductivity of One Lattice Constant

Abstract

Grazing angle ion-beam milling of c-axis oriented YBa₂Cu₃O₇ films is shown to give smooth films which have metallic-like resistance transitions and superconduct at thicknesses approaching a lattice constant. The zero resistance transition temperature decreases uniformly with increased milling with most of the change occurring for thicknesses less than 100Å. The crossover to non-superconducting behavior occurs at “electrical” thicknesses near 10 Å with a sheet resistance above the onset of the superconducting transition having a value near h/4e² = 6450Ω, a combination of fundamental constants predicted by theory and observed previously in low-T_c superconductors. Continued milling beyond this limit results in semiconducting behavior without a superconducting transition.