Theory of Solid State Physics group (Maekawa group) has revealed that the dc Josephson current is induced by a coupling between the ac Josephson current and the spin dynamics due to the ferromagnetic resonance (FMR) in a ferromagnetic Josephson junction, which is composed of two superconductors (SC's) separated by a ferromagnetic metal (FM). Since the ac internal magnetic field induced by the precessional motion of spin by FMR is coupled with the phase of superconducting order parameter, the Josephson current oscillates with difference between the frequency of the internal magnetic field and the Josephson frequency proportional to the voltage across the junction. As a result, the dc Josephson current is induced by FMR, when the frequency of the internal magnetic field is equal to the Josephson frequency. We call this phenomenon "ferromagnetic Josephson resonance", which provides a theoretical basis not only for studying the effect of dynamics on the ferromagnetic Josephson junctions but also for developing new superconducting devices such as solid state quantum bits. This work was introduced in J. Phys. Soc. Jpn. 77, 053707 (2008) and also reported in a news paper (Kagaku Shimbun, 2008. 5. 30).
Prof. Maekawa group（Theory of Solid State Physics）