Scanning tunneling microscopy/spectroscopy of ferromagnetic Ni clusters on graphite and BSCCO high-Tc superconductor

A brief description of the basic principles of the theory of scanning tunneling microscopy and spectroscopy is given. This paper presents results of our experimental investigations of Ni clusters deposited on ab-surface of Bi2Sr2CaCu2O8+y (BSCCO) single crystals or highly oriented pyrolytic graphite (HOPG) substrates. The microclusters were produced by the plasma gas condensation or evaporator with integral flux monitor. The scanning tunneling spectroscopy was performed at 24 K and at room temperature. The spectra measured above the Ni clusters and directly above the substrate reveal remarkable differences. Point contact tunneling (PCT) measurements on the overdoped regime Bi2Sr2CaCu2O8+y single crystals show sharp zero bias conductance peak (ZBCP) at zero bias voltage. The ZBCP observation gives strong evidence that the order parameter is of d-wave symmetry for overdoped BSCCO single crystals.