Dresden 2011 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 54: SC: Heterostructures, Andreev Scattering, Proximity Effect
TT 54.1: Vortrag
Donnerstag, 17. März 2011, 15:30–15:45, HSZ 301
Observation of Andreev bound states at spin-active interfaces — •Florian Hübler1,2, Michael J. Wolf1, Detlef Beckmann1, and Hilbert von Löhneysen2,3 — 1Karlsruher Institut für Technologie, Institut für Nanotechnologie — 2KIT, Institut für Festkörperphysik — 3KIT, Physikalisches Institut
Spin-active interfaces, for instance between superconductors and ferromagnets are characterized by spin-dependent transmission amplitudes as well as phase shifts[1]. The relative phase shift between spin-up and -down, the so-called spin-mixing angle θs, is an important parameter for the triplet proximity effect. So far, little quantitative information is available about θs. Recent theoretical models indicate that θs may actually be quite large in structures with ultra-thin tunnel barriers[2]. One of the consequences of finite θs in S/F hybrids is the presence of bound states at the interface[3], at energies which have a particularly simple relation to θs, є=± Δ cos(θs/2).
We report here the experimental observation of Andreev bound states induced by spin-mixing in Al/Al2O3/Fe structures. From the energy of the bound states, we can determine θs with great accuracy. As predicted theoretically, we find examples of θs ≈ Π, but also a significant spread from contact to contact, even within the same fabrication batch. The large spread indicates that spin mixing in real structures depends in a subtle way on details of the interface, and is possibly controlled by defects.
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