ABSTRACT
This chapter focuses on electron tunneling spectroscopy of thallium-based high-temperature superconducting (HTS) materials. The large range of tunneling gaps may be due to local variations in stoichiometry and crystallographic orientation of the electrodes not reflected in the Tc measurement of the sample. It is clear from the transport properties of HTS materials that they are highly anisotropic and that the grain boundaries in polycrystalline HTS materials act as Josephson junctions. In addition, the capability of scanning the surface of the sample allows for spatially resolved spectroscopy, commonly referred to as scanning tunneling spectroscopy (STS). It is also possible to incorporate single-crystal HTS electrodes into static (non-scanning) mechanically adjustable tunnel barrier junctions such as break junctions.
