Spin supercurrent, magnetization dynamics, andφ-state in spin-textured Josephson junctions

Abstract

The prospect of combining the dissipationless nature of superconducting currents with the spin-polarization of magnetic materials is interesting with respect to exploring superconducting analogues of topics in spintronics. In order to accomplish this aim, it is pivotal to understand not only how such spin-supercurrents can be created, but also how they interact dynamically with magnetization textures. In this paper, we investigate the appearance of a spin-supercurrent and the resulting magnetization dynamics in a textured magnetic Josephson current by using three experimentally relevant models: i) a superconductor|ferromagnet|superconductor (S|F|S) junction with spin-active interfaces, ii) a S|F 1 |F 2 |F 3 |S Josephson junction with a ferromagnetic trilayer, and iii) a Josephson junction containing a domain wall. In all of these cases, the supercurrent is spin-polarized and exerts a spin-transfer torque on the ferromagnetic interlayers which causes magnetization dynamics. Using a scattering matrix formalism in the clean limit, we compute the Andreev-bound states and resulting free energy of the system which in turn is used to solve the Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous magnetism influences the phase-dependence of the charge supercurrent as well as the magnetization dynamics caused by the spin-polarization of the supercurrent. Using a realistic experimental parameter set, we find that the spin-supercurrent can induce magnetization switching that is controlled by the superconducting phase difference. Moreover, we demonstrate that the combined effect of chiral spin symmetry breaking of the system as a whole with interface scattering causes the systems above to act as phase batteries that may supply any superconducting phase difference ϕ in the ground state. Such a ϕ junction is accompanied by an anomalous supercurrent appearing even at zero phase difference, and we demonstrate that the flow direction of this current is controlled by the chirality of the magnetization configuration.

Anomalous current in diffusive ferromagnetic Josephson junctions

“…For any coplanar magnetization distribution there exists a global SU(2) spin rotation that flips the direction of M, and the condition (3) is fulfilled. For this reason, the AJE requires a noncoplanar magnetization texture as predicted for ballistic S/F/F/F/S systems [32][33][34]. The anomalous current obtained in those works shows rapid oscillations as a function of the ferromagnetic thickness.…”

Magnetization-induced dynamics of a Josephson junction coupled to a nanomagnet

“…30. Furthermore, the dynamics of both JJs with misaligned ferromagnetic layers and those coupled to single or multiple ferromagnetic layers have also been studied numerically 31 . It has also been shown that the presence of a single classical spin of a molecular magnet precessing under the action of a constant magnetic field coupled to a JJ may lead to generation of finite spin current whose polarization axis rotates with same frequency as the classical spin 32 .…”

Josephson response of a conventional and a noncentrosymmetric superconductor coupled via a double quantum dot

“…Such junctions have been predicted to occur in ferromagnetic Josephson junctions with spinorbit interactions [30], in Josephson junctions containing a multilevel quantum dot with spin-orbit coupling and a magnetic field [31], in Josephson junctions with spinorbit nanowires subject to magnetic fields [32], in multiterminal quantum-dot Josephson junctions subject to frustration between 0 and π states [33], and in complex ferromagnetic Josephson junctions [34][35][36][37]. In the latter type of setup, the occurrence of a ϕ junction has recently been confirmed experimentally [38].…”