Extremely long-range, high-temperature Josephson coupling across a half-metallic ferromagnet.

Area of Science:

• Condensed Matter Physics
• Quantum Materials Science

Background:

• Josephson effect describes superconducting coupling across a spacer, crucial for quantum states.
• Achieving long-range Josephson effects in ferromagnetic junctions has been a significant challenge.

Purpose of the Study:

• To demonstrate extremely long-range Josephson coupling at high temperatures.
• To explore the potential of combining high-temperature superconductors with ferromagnetic materials for advanced applications.

Main Methods:

• Fabrication of planar Josephson junctions using La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (a half-metallic manganite) and YBa$_{2}$Cu$_{3}$O$_{7}$ (a superconducting cuprate).
• Characterization of junction properties including critical currents and response to magnetic flux and microwave excitation.

Main Results:

• Demonstrated micrometric, high-temperature (tens of kelvins) Josephson coupling.
• Observed large critical currents, magnetic flux-driven critical current oscillations, and Shapiro steps.
• Noted an anomalous doubling of Josephson frequency under microwave excitation, consistent with theoretical predictions.

Conclusions:

• The study successfully demonstrates a novel approach to achieving long-range, high-temperature Josephson coupling.
• The findings pave the way for superconducting spintronics and offer new avenues for quantum computing.
• The observed phenomena provide valuable insights into fundamental Josephson physics in complex heterostructures.