Abstract
Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved (BSCCO) samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a scanning tunneling microscope (STM) equipped with a superconducting tip. The spatial resolution of the STM of lateral distances less than the superconducting coherence length allows it to reveal local inhomogeneities in the pair wave function of the BSCCO. Instrument performance is demonstrated first with Josephson measurements of Pb films followed by the layered superconductor . The relevant measurement parameter, the Josephson product, is discussed within the context of both BCS superconductors and the high transition temperature superconductors. The local relationship between the product and the quasiparticle density of states (DOS) gap are presented within the context of phase diagrams for BSCCO. Excessive current densities can be produced with these measurements and have been found to alter the local DOS in the BSCCO. Systematic studies of this effect were performed to determine the practical measurement limits for these experiments. Alternative methods for preparation of the BSCCO surface are also discussed.
19 More- Received 10 August 2009
DOI:https://doi.org/10.1103/PhysRevB.80.144506
©2009 American Physical Society