Direct Observation of Spin-State Mixing in Superconductors

We observe a peak in the tunneling conductance between two very thin superconducting aluminum films in an intense parallel magnetic field at a voltage $V=\frac{({\Delta }_1+{\Delta }_2-2\mathrm{}\mu H)}{e}$. The magnetic field dependence of this peak identifies it as that predicted by Engler and Fulde for spin-state mixing in superconductors. The spin-orbit scattering rate $b=\frac{\hslash }{3\Delta }{\tau }_{\mathrm{s}.\mathrm{o}.\mathrm{}}$ obtained from this measurement is approximately 0.1.