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Degenerate ground state in a mesoscopic YBa2Cu3O(7-x) grain boundary Josephson junction
E Il'ichev1, M Grajcar, R Hlubina
1Department of Cryoelectronics, Institute for Physical High Technology, P.O. Box 100239, D-07702 Jena, Germany.
Physical Review Letters
|June 1, 2001
Summary
We observed unique Josephson current behaviors in YBa2Cu3O7-x grain boundary Josephson junctions, deviating from standard tunnel junctions. These findings align with models for d-wave superconductors.
Area of Science:
- Solid State Physics
- Superconductivity
- Materials Science
Background:
- Understanding Josephson junctions is crucial for superconducting electronics.
- Conventional tunnel junctions exhibit predictable current-phase relationships.
- High-temperature cuprate superconductors like YBa2Cu3O7-x present unique electronic properties.
Purpose of the Study:
- To investigate the current-phase relationship (I(φ)) in YBa2Cu3O7-x grain boundary Josephson junctions.
- To identify deviations from conventional tunnel-junction behavior.
- To compare experimental results with microscopic models of d-wave superconductors.
Main Methods:
- Fabrication of symmetric 45-degree YBa2Cu3O7-x grain boundary Josephson junctions.
- Measurement of the current-phase relationship I(φ) as a function of temperature (T).
- Analysis of the critical current and harmonic components of the I(φ) relationship.
Main Results:
- Observed a local minimum in critical current at a specific temperature T*.
- Noted a sign change in the first harmonic of I(φ) around T*.
- Found the second harmonic comparable to the first for T < T*.
- Identified degeneracy in the junction's ground state below T*.
Conclusions:
- The observed phenomena indicate substantial deviations from conventional tunnel-junction behavior.
- Experimental results are consistent with a microscopic model for Josephson junctions involving d-wave superconductors.
- These findings contribute to the understanding of unconventional superconductivity in cuprates.
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