Condensed Matter Physics Seminar

Friday, April 9, 1999, 2 p.m.
Plant Sciences Building, Room 1130

Spin polarized tunneling and Andreev reflection in ferromagnet/superconductor junction

Igor Zutic

(University of Maryland)

Abstract:  In recent years it became possible to fabricate high quality ferromagnet/superconductor (F/S) structures with small interfacial resistance. Interests in these structures range from examining the basic properties of spin polarized transport in unconventional superconductors to the design of novel devices.  We study tunneling in F/S junctions and include the effects of spin polarization, interfacial resistance, and Fermi wavevector mismatch (FWM) between the F and S regions. Andreev reflection at the F/S interface, governing tunneling at low bias voltage, is strongly modified by these parameters. The conductance exhibits a very wide variety of features as a function of applied voltage. It displays novel behavior, different from that found in unpolarized tunneling into an unconventional superconductor or in an F/conventional superconductor junction.  We show that, in the presence of FWM, spin polarization can enhance Andreev reflection and give rise to a zero bias conductance peak even for an s-wave superconductor.  We discuss possible implications of our results for interpreting recent experiments [R.J.Soulen et al., Science 282, 84 (1998)] which measure spin polarization in various materials by examining the behavior of differential conductance.

Host: Sankar Das Sarma

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