Electron tunnelling and critical current behaviour of patterned Y₁Ba₂Cu₃O_{7 - δ} films

We report on point contact tunnelling experiments on preferentially c oriented Y₁Ba₂Cu₃O_7-δ (123) films deposited onto (100) SrTiO₃ substrates using an ultra-high vacuum (UHV) triple electron-gun system with BaF₂, yttrium and copper as source materials. The films were coated with a thin silver layer and annealed at 450°C. A niobium point was then carefully brought into contact with the surface, which was investigated by electron tunnelling. Using 10 GHz radiation we identified microwave-induced current steps in the current-voltage characteristic. Also, there was a strong decrease in Josephson current on application of a magnetic field. Moreover, UHV films were patterned into strips as narrow as 10 μm using a reactive ion etching technique. Critical current densities of about 10⁶ A cm^-2 at 20 K were obtained, which is an order of magnitude larger than for sputtered films, but smaller than for UHV laser-patterned thinner films.