Josephson scanning tunneling microscopy: A local and direct probe of the superconducting order parameter

Hikari Kimura, R. P. Barber, Jr., S. Ono, Yoichi Ando, and R. C. Dynes
Phys. Rev. B 80, 144506 – Published 6 October 2009

Abstract

Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi2Sr2CaCu2O8+δ (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 NbSe2. The relevant measurement parameter, the Josephson ICRN product, is discussed within the context of both BCS superconductors and the high transition temperature superconductors. The local relationship between the ICRN 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.

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  • Received 10 August 2009

DOI:https://doi.org/10.1103/PhysRevB.80.144506

©2009 American Physical Society

Authors & Affiliations

Hikari Kimura1,2,*, R. P. Barber, Jr.3, S. Ono4, Yoichi Ando5, and R. C. Dynes1,2,6,†

  • 1Department of Physics, University of California, Berkeley, California 94720, USA
  • 2Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
  • 3Department of Physics, Santa Clara University, Santa Clara, California 95053, USA
  • 4Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511, Japan
  • 5Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
  • 6Department of Physics, University of California–San Diego, La Jolla, California 92093-0319, USA

  • *Present address: Department of Physics and Astronomy, University of California, Irvine, California 92697, USA.
  • rdynes@ucsd.edu

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Vol. 80, Iss. 14 — 1 October 2009

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