Sign reversal of ac Josephson current in a ferromagnetic Josephson junction

It is known that in a superconductor/insulator/superconductor (SIS) junction, when a finite voltage is applied, the Josephson current shows a logarithmic divergence, i.e., the so-called Riedel peak(RP) at the gap voltage, $V$=2$\Delta $/e, ($\Delta $ is a superconducting gap). In a double barrier Josephson junction such as SXS junction, on the other hand, the voltage dependence of $I_{c}$ has not been investigated so far, where X is a normal metal (N) or a ferromagnet (F). We study the voltage dependence of Josephson critical current ($I_{c})$ in a variety of SXS junctions. In a SNS junction, $I_{c }$shows the RP at the gap voltage similar to a SIS junction. On the other hand, in a SFS junction, $I_{c}$ shows a damped oscillation with the alternation of sign as a function of thickness ($d)$ of F due to 0-$\pi $ transition. The RP exhibits a strong dependence on $d$, and changes its sign. It is predicted that the RP disappears at the 0-$\pi $ transition in the SFS junction.