Josephson currents and spin-transfer torques in ballistic SFSFS nanojunctions

Utilizing a full microscopic Bogoliubov–de Gennes (BdG) approach, we study the equilibrium charge and spin currents in ballistic SFSFS Josephson systems, where F is a uniformly magnetized ferromagnet and S is a conventional s-wave superconductor. From the spatially varying spin currents, we also calculate the associated equilibrium spin-transfer torques. Through variations in the relative phase differences between the three S regions, and magnetization orientations of the ferromagnets, our study demonstrates tunability and controllability of the spin and charge supercurrents. The spin-transfer torques are shown to reveal details of the proximity effects that play a crucial role in these types of hybrid system. The proposed SFSFS nanostructure is discussed within the context of a superconducting magnetic torque transistor. (paper)