Superconductors are an essential part of our future technology, in particular to create devices used for quantum computing. Superconductors are materials that can conduct electricity without any electronic resistance, which means that electrons can move through the material without any loss of energy. The behavior of bulk superconducting materials is described by the BCS theory, stating that superconductivity occurs when two electrons are held together by lattice vibrations. However, when superconductors are very small, their behavior can change and is hard to predict.
Superconductivity of ultrathin layers
The main goal of the study was to understand how superconductivity changes in reduced dimensions. “For the case of aluminum, the superconducting state in thin films can survive up to higher temperatures compared to the bulk material, but we do not exactly know why this happens. A very thin superconductor becomes sensitive to its environment and therefore, it is hard to determine the intrinsic properties of the material”, researcher Werner van Weerdenburg explains.
The research team used state-of-the-art growth techniques to grow films of aluminum under very clean conditions. Using a scanning tunneling microscope, the morphology of these films as well as the superconducting properties could be measured. Interestingly, they found that the very thin and clean layers of aluminum show a larger temperature at which the material becomes superconducting. This finding suggests that the enhanced superconductivity state is intrinsic to aluminum. Moreover, the researchers showed that the superconducting state of these films is extremely robust against the application of in-plane magnetic fields. “The combination of high fields and superconductivity is a unique regime where unconventional types of pairing can exist. By studying the shape of the vortex in large magnetic field, we could infer the presence of such unconventional pairs.”