Sign reversal of ac Josephson current in a ferromagnetic Josephson junction

TL;DR

This paper investigates the ac Josephson effect in ferromagnetic junctions, revealing sign reversals of currents due to 0-$f ext{pi}$ transitions and unique features like Riedel peak reversal, contrasting with conventional junctions.

Contribution

It provides a detailed theoretical analysis of the sign reversal phenomena and the behavior of Josephson and quasiparticle currents in ferromagnetic Josephson junctions.

Findings

Josephson and quasiparticle currents change sign with ferromagnetic layer thickness.

Riedel peak shows reversal and disappears near the 0-$f ext{pi}$ transition.

Distinct behaviors contrast with conventional Josephson junctions.

Abstract

The ac Josephson effect in a ferromagnetic Josephson junction, which is composed of two superconductors separated by a ferromagnetic metal (FM), is studied by a tunneling Hamiltonian and Green's function method. We obtain two types of superconducting phase dependent current, i.e., Josephson current and quasiparticle-pair-interference current (QPIC). These currents change their signs with thickness of the FM layer due to the 0-$\pi$ transition characteristic to the ferromagnetic Josephson junction. As a function of applied voltage, the Josephson critical current shows a logarithmic divergence called the Riedel peak at the gap voltage, while the QPIC shows a discontinuous jump. The Riedel peak reverses due to the 0-$\pi$ transition and disappears near the 0-$\pi$ transition point. The discontinuous jump in the QPIC also represents similar behaviors to the Riedel peak. These results are in contrast to the conventional ones.