Microwave-induced supercurrent in a ferromagnetic Josephson junction
強磁性ジョセフソン接合中のマイクロ波で誘起された超伝導電流
挽野 真一*; 森 道康 ; 高橋 三郎*; 前川 禎通
Hikino, Shinichi*; Mori, Michiyasu; Takahashi, Saburo*; Maekawa, Sadamichi
We study the supercurrent resulting from coupling of the Josephson-phase and the spin-wave excited by microwave radiation in a ferromagnetic Josephson junction, in which two superconductors are separated by a ferromagnet. To explore how the spin wave excitation affects the current-voltage curve, the resistively shunted junction model, which is an equation of motion for the Josephson-phase, is extended by considering the gauge invariance including magnetization. When the magnetization is driven by the microwave adjusted to the ferromagnetic resonance frequency, the dc supercurrent is induced in the junction, and the current-voltage curve shows step structures as a function of applied voltage. The position of each step in voltage is proportional to the microwave frequency multiplied by even number. This means that the even number of magnons is necessary for the singlet Cooper pair to go through the ferromagnetic layer. The magnitudes of step-height can be controlled by tuning the shape of interface. Our results present a new route to observe the spin-wave excitation by the Josephson effect.