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We
have studied the electronic density of states in a mesoscopic aluminum wire
near a transparent interface with a ferromagnetic nickel metal. In our tunnel
spectroscopy experiment, a substantial density of states is observed at
sub-gap energies close to a ferromagnet. We compare our data with detailed
calculations based on the Usadel equation, where the effect of the
ferromagnet is treated as an effective boundary condition. We achieve an
excellent agreement with theory when non-ideal quality of the interface is
taken into account.
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Above: Normalized differential conductance of a tunnel probe, when
properties of S are affected by the proximity of a ferromagnet. The
circles are the experimental data at a distance of 180 nm the interface,
and that for the bulk Al (measured at T = 100 mK). The solid curves are
the best fits to theory, with alpha = 7.5, E_C / Delta = 1.5, r_b = 3. The
gap of Al was Delta = 0.22 mV.
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