Nanoscale Superconductivity

A nanoscale coherence length is a key property of high temperature superconductors. Point Contact and STM spectroscopy can be used to reveal the effect of nanoscale faceting on the order parameter (1,2). These studies are fundamental for the development of tunneling and Josephson devices. Another kind of device being studied consists of a two ferromagnetic nanowires connected to a superconducting base. They allow in principle to propagate the two electrons of a Cooper pair in physically separate channels, which can form the basis for producing entangled states for quantum computing (3). In these devices, the distance between the two ferromagnetic wires must be in the nanometer range. Another field of study is that of composite metal/insulator mixtures, which behave as three dimensional arrays of weakly coupled metallic nanodots. Transport properties in these structures are extremely sensitive to the composition, they range from metallic to insulators, and can even be super-insulators when the metallic grains are superconducting due to the opening of the energy gap (4). They are model systems for the study of very low superfluid density condensates.