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 Phi(S) 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 I-ca depends on Phi(S). We derive the self-consistency equation describing the critical temperature T-c of the SF sandwich under nonequilibrium conditions. In addition, we compute I-ca by solving the Boltzmann equation for the electron distribution function f(epsilon), which then allows a determination of the relative change of delta I-ca/delta I-i(V-i) versus the bias voltage V-i and the injection current I-i(V-i). The computed gain delta I-ca/delta I-i(V-i) strongly depends on delta I-ca/delta I-i(V-i), and agrees well with the experimental data.