Control of Superconductivity in a Hybrid Superconducting/Ferromagnetic Multilayer Using Nonequilibrium Tunneling Injection

We report a theoretical and experimental study on the use of nonequilibrium tunneling injection to control the local Cooper pair amplitude ΦS in an SF sandwich involving superconducting (S) and ferromagnetic (F) layers coupled by the proximity effect. In an SISFIFS structure (where I is an insulator), this same SF sandwich serves as the acceptor electrode of an SISF Josephson junction whose critical current Ica depends on ΦS. We derive the self-consistency equation describing the critical temperature Tc of the SF sandwich under nonequilibrium conditions. In addition, we compute Ica by solving the Boltzmann equation for the electron distribution function f, which then allows a determination of the relative change of δIca/δIi(Vi) versus the bias voltage Vi and the injection current Ii(Vi). The computed gain δIca/δIi(Vi) strongly depends on δIca/δIi(Vi), and agrees well with the experimental data.