Scanninng Josephson Tunneling Microscopy of Single Crystal Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ from a Conventional Superconducting Tip

Using a scanning tunneling microscope with superconducting Pb-coated tips (S-STM), we have observed the thermally fluctuated Josephson Effect between the tip and conventional superconductors. Such STM-based Josephson junctions are a powerful tool that can directly probe the phase of the superconducting condensate via the Josephson Effect as well as characterize the quasiparticle spectrum, both on a nanometer length scale. In this talk we present data from Josephson junctions formed between the S-STM tips and Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ single crystals. These results clearly show c-axis Josephson tunneling between a conventional superconductor and both overdoped and optimally doped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$. Josephson measurements at various surface locations indicate an inhomogeneous structure of the I$_{C}$R$_{N}$ product in overdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$. These local I$_{C}$R$_{N}$ data of the Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ are related to the local superconducting gap. This work is supported by DOE Grant No. DE-FG02-05ER46194.