Zero-Field Fiske Resonance Coupled with Spin-waves in Ferromagnetic Josephson Junctions

TL;DR

This paper theoretically investigates zero-field Fiske resonance coupled with spin-waves in a ferromagnetic Josephson junction, revealing how resonant peaks in the I-V characteristics emerge without external magnetic fields due to composite excitations.

Contribution

It introduces a theoretical model for zero-field Fiske resonance coupled with spin-waves in ferromagnetic Josephson junctions with non-uniform barriers, highlighting novel resonance phenomena.

Findings

Resonant peaks in I-V curves due to spin-wave and EM field coupling.

Resonance occurs without external magnetic field due to non-uniform barrier.

Voltage at resonance relates to EM normal modes.

Abstract

AC Josephson current density in a Josephson junction with DC bias is spatially modulated by an external magnetic field, and induces an electromagnetic (EM) field inside the junction. The current-voltage ($I$-$V$) curve exhibits peaks due to the resonance between the EM field and the spatially modulated AC Josephson current density. This is called {\it Fiske resonance}. Such a spatially modulated Josephson current density can be also induced by a non-uniform insulating barrier and the Fiske resonance appears without external magnetic field. This is called zero-field Fiske resonance (ZFFR). In this paper, we theoretically study the ZFFR coupled with spin-waves in a superconductor/ferromagnetic insulator/superconductor junction (ferromagnetic Josephson junction) with a non-uniform ferromagnetic insulating barrier. The resonant mode coupled with spin-waves can be induced without external magnetic field. We find that the $I$-$V$ curve shows resonant peaks associated with composite excitations of spin-waves and the EM field in the junction. The voltage at the resonance is obtained as a function of the normal modes of EM field. The ZFFRs coupled with spin-waves are found as peak structures in the DC Josephson current density as a function of bias voltage.