SPECTROSCOPY OF A SINGLE SUPERCONDUCTING FINE-PARTICLE USING A SCANNING TUNNELING MICROSCOPE

We have carried out spectroscopy of a single superconducting fine part icle using a scanning tunneling microscope (STM). We observed the supe rconducting energy gap by making the tunnel resistance between the STM tip and the particle very low to avoid the Coulomb blockade. We measu red the particle-size dependence of the spacing between the two peaks 2 Delta(p-p) in the tunneling spectrum. It is found that 2 Delta(p-p) increases with decreasing particle diameter from 250 Angstrom to 50 An gstrom. We discuss the result in connection with the fluctuation of th e order parameter.