Electron Tunneling Measurements of High-Tc Superconductor Bi-Sr-Ca-Cu-O by STM

Abstract

The tunneling spectra of T _c=80 K single crystal and 110 K polycrystalline specimens have been measured at 4 K using a scanning tunneling microscope with a tungsten counter electrode. For the 80 K phase, we estimated the energy gaps 2Δ/k _B T _c to be 4.9–5.3 and 4.2–5.0 in the directions perpendicular and parallel to the a-b plane, respectively, while 2Δ/k _B T _c for the 110 K phase was in the range of 3.4–4.2. The energy gap data obtained in the present study will be discussed in terms of the anisotropy and coupling strength of the superconductivity.