Spin-Polarized Electron Tunneling Study of an Artificially Layered Superconductor with Internal Magnetic Field: EuO-Al

Abstract

The tunneling conductance of junctions formed on thin films of Al in contact with films of the ferromagnetic semiconductor EuO implies that such composites behave like BCS superconductors with internal magnetization. In a magnetic field $B$ applied in the plane of the films, the superconducting quasiparticle density of states shows a splitting $2\mu (B^{*}+B)$, where $B^{*}$ can be greater than $B$ by more than a tesla. The critcal field of composite films is reduced by approximately $B^{*}$ compared to that of identical Al films without EuO. The observed $B^{*}$ is of the same magnitude as $\mu {}_0{}^{}{}_{}{}^{}M$, the magnetization of EuO.