Dresden 2003 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 20: Postersitzung IV (Mesoskopische Systeme, Supraleitung: Massivmaterialien, Bandleiter, Pinning, Vortexdynamik, Transporteigenschaften, Korngrenzen)

TT 20.13: Poster

Donnerstag, 27. März 2003, 14:30–19:00, P2c, P2d

S/N and S/FM point contacts through silicon-nitride membranes — •F. Perez-Willard¹, C. Sürgers¹, H. v. Löhneysen^1,2, and P. Pfundstein³ — ¹Physikalisches Institut and Center for Functional Nanostructures, Universität Karlsruhe, D-76128 Karlsruhe — ²Forschungszentrum Karlsruhe, Institut für Festkörperphysik, D-76344 Karlsruhe — ³Laboratorium für Elektronenmikroskopie, Universität Karlsruhe, D-76128 Karlsruhe

We report on low-temperature (20 mK - 2 K) measurements of the electrical differential resistance R=dU/dI vs. voltage U of superconductor (S)/normal metal (N) and S/ferromagnet (FM) point contacts. The samples consist of an insulating 50-nm thick silicon-nitride membrane in which a single nanohole of diameter d ≤ 50 nm has been patterned previously by means of e-beam lithography and reactive ion etching. 200 nm aluminum (S) and X nm (X=0, 6, 12, 24, 52) cobalt (FM) plus (200−X) nm copper are deposited under ultra-high vacuum conditions on either side of the membrane. The R−U spectra for the S/N contacts can be described well for all temperatures T within the BTK-Theory [1]. For the S/FM contacts, X≠0 causes a dramatic change in the shape of the spectrum compared to X=0. By further increasing X the amplitude of the spectrum is slightly reduced. An analysis of similar S/FM spectra has been used before to estimate the degree of spin polarization in the ferromagnetic metal [2]. The applicability of this procedure and the magnetic-field dependence of the spectra will be discussed.

[1] G. E. Blonder et al., Phys. Rev. B 25, 4515 (1982).

[2] R. J. Soulen et al., Science 282, 85 (1998).