National Synchrotron Light Source Seminar

Low-dimensional superconductivity has been the subject of intense interest for decades. One of the key open questions in superconductivity concerns its detailed properties in confined geometries at the nanoscale, particularly the size limits for which a real physical system can maintain global and local superconducting phase coherence. I will systematically address this fundamental issue via a detailed scanning tunneling microscopy/spectroscopy (STM/STS) study of Pb superconducting islands with different thicknesses and lateral sizes supported on Si(111). As the lateral dimension of an island is reduced, suppression of the superconducting gap D depends to a good approximation only on the volume of the island, being largely independent of its shape. We have discovered an intriguing lateral proximity effect on Pb nano-islands; an island with a higher transition temperature can induce superconductivity in a nearby island with a lower transition temperature. By measuring the spatial mapping of the local superconducting gap, we also experimentally determine a lateral “proximity” length. When an island is smaller than the proximity length, it is found that superconductivity within the island is rather uniform, indicating the rigidity of the order parameter on the scale of proximity length.