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Condensed Matter Physics Seminar

Thursday, September 21, 2000, 2 p.m.

Plant Sciences Building, Room 1130
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*Theory of Andreev Reflection at the Superconductor-Ferromagnet Boundary*

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Igor Mazin

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(Naval Research Laboratory, Washington, DC)

**Abstract:** Andreev reflection (AR) at a boundary between a
ferromagnet and a superconductor is a new and promising method for probing
the degree of spin polarization (DSP) at the Fermi level. Unfortunately,
as with all others methods, it is not clear which combination of the density
of states, Fermi velocity, and possibly additional matrix elements, defines
the measured DSP. A further complication in case of AR is the lack
of a complete theory, taking into account evanescent wave matching the
Cooper pairs for spin-forbidden AR, even in the ballistic regime, and lack
of *any* theory in the diffusive regime. Furthermore, nearly
all theoretical work on this subject makes use of the one-parabolic-band
model with a *k*-independent exchange splitting. While theoretically
appealing, this model bears no relevance to the processes in the real *d*-electron
ferromagnets. Thus the requested theory must also be able to handle arbitrary
bands and arbitrary Fermi surface geometry in both spins, as well as in
the superconducting lead. I will present such a theory for both ballistic
and diffusive regimes, making particular emphasis on the role of the Fermi
surface geometry and on some practical aspects of processing results of
the AR measurements.
**Host:** Victor Yakovenko

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