Thickness dependence of the superconducting properties of ultra-thin Bi2Sr2CaCu2O8+xsingle crystals

With a cleaving technique and Ar-ion etching, we make ultra-thin bridges from Bi2Sr2CaCu2O8+x single crystals. Superconductivity can be observed in the bridges only a few unit cells thick. A superconductor–insulator transition occurs when the thickness is lower than 4.5 nm. The two-dimensional nature of the superconducting transition is examined in these ultra-thin samples. We see deviations from the usual Kosterlitz–Thouless-type behaviour and discuss a possible explanation.