Composite excitation of Josephson phase and spin waves in Josephson junctions with ferromagnetic insulator

TL;DR

This paper theoretically investigates the coupling between Josephson-phase and spin-waves in superconductor/ferromagnetic insulator/superconductor junctions, revealing resonant peaks in the I-V characteristics due to composite excitations.

Contribution

It introduces a theoretical model combining Maxwell and Landau-Lifshitz-Gilbert equations to analyze coupled electromagnetic and spin-wave dynamics in S/FI/S junctions, identifying multiple resonant peaks.

Findings

Resonant peaks in I-V characteristics due to coupled excitations

Voltages at resonances depend on EM normal modes

Additional peaks appear with nonmagnetic insulator interface

Abstract

Coupling of Josephson-phase and spin-waves is theoretically studied in a superconductor/ferromagnetic insulator/superconductor (S/FI/S) junction. Electromagnetic (EM) field inside the junction and the Josephson current coupled with spin-waves in FI are calculated by combining Maxwell and Landau-Lifshitz-Gilbert equations. In the S/FI/S junction, it is found that the current-voltage (I-V) characteristic shows two resonant peaks. Voltages at the resonant peaks are obtained as a function of the normal modes of EM field, which indicates a composite excitation of the EM field and spin-waves in the S/FI/S junction. We also examine another type of junction, in which a nonmagnetic insulator (I) is located at one of interfaces between S and FI. In such a S/I/FI/S junction, three resonant peaks appear in the I-V curve, since the Josephson-phase couples to the EM field in the I layer.