| The scanning tunneling microscope (STM) has proved to be an important tool in the study of superconductors, offering a local probe of the superconducting density of states. STM experiments have so far employed normal-metal tips, thus probing only the quasiparticle spectrum-excitations on the superconducting state. In unconventional superconductors, the lack of a theory that would help correlate between quasiparticle spectra and superconductivity calls for a direct measurement of the local pair amplitude. This can be achieved by using superconducting STM tips to form a scannable Josephson junction—the Josephson STM.; This thesis describes the implementation of such a device, from the fabrication of reproducible superconducting Pb/Ag tips to the study of the Josephson effect in STM based, ultra-small vacuum junctions. It was found that the pair current in these junctions appear as a peak in the current-voltage characteristics near zero bias, for junction resistances smaller than 100 kΩ. The shape of the current-voltage characteristics, the magnitude of the supercurrent peak as a function of the junction resistance, and the microwave response of the junctions, are in excellent agreement with the classical phase diffusion model. A procedure that was developed for the measurement of the Josephson product, IcRN, from the tunneling characteristics in superconducting STM junctions, will be discussed. Results will be presented for tunneling into Pb films, and NbSe2 and Bi2Sr 2CaCu2O8 crystals. |
