Very large thermophase in ferromagnetic Josephson junctions

Area of Science:

• Condensed Matter Physics
• Superconductivity
• Thermoelectric Effects

Background:

• A thermophase is a phase gradient in a superconductor due to a temperature bias.
• Supercurrents can counterbalance quasiparticle currents, preventing voltage drops (thermovoltages).
• Thermophases are also expected in Josephson-coupled superconductors.

Purpose of the Study:

• To theoretically investigate the thermoelectric response of a thermally biased Josephson junction incorporating a ferromagnetic insulator.
• To predict the magnitude of the thermophase in such a system.

Main Methods:

• Theoretical analysis of a Josephson junction with a ferromagnetic insulator under a temperature bias.
• Calculation of thermoelectric response, focusing on thermophase magnitude.

Main Results:

• Prediction of a significantly large thermophase, potentially reaching π/2 across the junction.
• Quasiparticle thermal current can approach the critical current.
• Observed thermophase magnitudes are orders of magnitude larger than in conventional Josephson tunnel junctions.

Conclusions:

• The proposed Josephson junction design with a ferromagnetic insulator exhibits a substantial thermophase.
• This effect offers potential for highly sensitive detection of minute temperature differences in low-temperature applications, such as sensing thermal radiation.