Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 26: Transport - Poster Session
TT 26.30: Poster
Mittwoch, 29. März 2006, 14:30–18:30, P1
Absence of fractional conductance quantization in ferromagnetic atomic contacts — •Michael Häfner1, Juan-Carlos Cuevas1,2,3, Janne Viljas1, Diego Frustaglia3, and Fabian Pauly1 — 1Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe, Germany — 2Departamento de Física Teórica de la Materia Condensada C-V, Universidad Autónoma de Madrid, 28049 Madrid, Spain — 3Quantum Transport and Information, Scuola Normale Superiore, 56126 Pisa, Italy
In this work we present a theoretical analysis of the current through atomic contacts of ferromagnetic materials (Co and Ni). Several experimental groups have recently reported the observation of half-integer conductance quantization in nanowires of these materials. This suggests that the current in these contacts is completely spin polarized and all the contributing channels are perfectly transmissive. In order to analyze these surprising observations, we have performed conductance calculations of Ni and Co atomic junctions based on a tight-binding model. Contrary to these experiments, we find that the conductance is in general neither quantized nor spin polarized. We show that the transport is mainly dominated by both the s and d bands close to the Fermi energy. These bands give rise to several conduction channels that are partially open. Typically, both spin bands give a significant contribution to the transport suggesting that the fractional conductance quantization should not appear in ferromagnetic atomic contacts.