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Published on: August 2, 2019
Coherent Subgap Transport in Spin-Split Josephson Junctions
David Caldevilla-Asenjo1, Gorm Ole Steffensen2, Sara Catalano1,3
1Centro de Fisica de Materiales, CSIC-UPV/EHU, 20018 Donostia-San Sebastian, Spain.
Physical Review Letters
|May 15, 2026
Summary
We observed subgap transport in ferromagnetic insulator-superconductor junctions, revealing spin-splitting effects in superconductors. This demonstrates a new platform for studying spin-polarized superconducting phenomena.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Phenomena
Background:
- Superconducting junctions are crucial for quantum electronics.
- Understanding spin-polarized transport in superconductors is key for spintronics.
- Ferromagnetic insulators offer unique ways to control superconducting properties.
Purpose of the Study:
- To experimentally observe subgap transport in ferromagnetic insulator-superconductor-insulator-superconductor junctions.
- To investigate the influence of spin-splitting on multiple Andreev reflection peaks.
- To establish a novel platform for studying spin-polarized superconducting phenomena.
Main Methods:
- Fabrication of vertical EuS/Al/AlOx/Al junctions.
- Differential conductance measurements to analyze subgap transport.
- Quasiclassical transport modeling to extract spin-splitting and transmission channel distribution.
Main Results:
- First experimental observation of subgap transport in these junctions.
- Multiple Andreev reflection peaks observed, with odd-order peaks showing spin-splitting.
- Even-order peaks remained unaffected by spin-splitting.
- Josephson current confirmed strong superconducting coupling.
- Identified approximately a hundred highly transmitting channels dominating transport.
Conclusions:
- A single spin-split superconductor is sufficient to observe the even-odd multiple Andreev reflection effect.
- EuS/Al junctions serve as a versatile platform for studying subgap transport, Josephson coupling, and spin-polarized superconductivity.
- The findings pave the way for advanced spintronic devices.
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