Josephson Interferometry Measurements in High-Tc Grain Boundary Junctions
Neils, William K.
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Permalink
https://hdl.handle.net/2142/30831
Description
Title
Josephson Interferometry Measurements in High-Tc Grain Boundary Junctions
Author(s)
Neils, William K.
Issue Date
2002
Director of Research (if dissertation) or Advisor (if thesis)
Van Harlingen, Dale J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
grain boundary interface
Superconductors
Josephson superconductors
Language
en
Abstract
We study Josephson junctions formed at grain boundary interfaces in the high-Tc cuprate
materials. The inherent properties of these Josephson junctions depend strongly on the pairing
symmetry and the electronic structure at the interface and can be used to determine the
pairing symmetry as well as the structure of the grain boundary interface. Andreev reflection
at the (110) surface in d-wave superconductors leads to the formation of zero-energy
quasiparticle surface states. It is predicted that these surface states lead to a suppression of
the d-wave order parameter and formation of a subdominant pairing phase with a complex
order parameter characterized by broken time-reversal symmetry. A similar phenomenon is
predicted to occur in the bulk film near magnetic impurities. Calculations demonstrate that
the temperature and magnetic field dependence of the critical current of 45° asymmetric
grain boundary Josephson junctions are extremely sensitive to the onset of a complex order
parameter. We have measured the critical current behavior of grain boundary junctions of
YBCO and BSCCO as well as Ca, Co, Ni, and Pr doped YBCO in an effort to observe the
onset a complex order parameter. We see no conclusive evidence for the existence of broken
time-reversal symmetry due to a complex order parameter. We do distinct see evidence of
second-order Josephson tunneling in a 45° asymmetric BSCCO junction in the form of a
critical current peak at zero applied magnetic field. The modulation length of this peak is
half that of the others and it exhibits a distinct temperature dependence consistent with a
second-order sin(2¢) critical current component.
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