Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 87: Graphen: Spin Transport (jointly with MA, DS, DY, O, TT)

HL 87.4: Talk

Thursday, March 29, 2012, 16:15–16:30, H 1012

Anisotropic super-spin at the end of a carbon nanotube — •Manuel J. Schmidt — RWTH-Aachen, Deutschland

The interplay of edge magnetism and spin-orbit interactions is studied theoretically on the basis of zigzag ends of carbon nanotubes. Spin-orbit coupling, generally weak in ordinary graphene, is strongly enhanced in nanotubes and thus cannot be neglected at low energies. In the present case it leads to a magnetic anisotropy on the order of 10 mK. Also the relation to correlated topological edge states is shortly discussed.

Carbon nanotubes with zigzag ends have localized electronic states at those ends. These localized states correspond to the edge states in graphene and are equally susceptible to Coulomb interactions. The latter drive a transition, known as edge magnetism in graphene. However, due to the very limited spatial size of this magnetic state, it should not be considered as a symmetry broken state but rather as a super-spin, composed of a few individual electron spins. Without spin-orbit interaction, the ground state of this super-spin would be 2S+1 fold degenerate. Finite spin-orbit coupling, however, breaks this degeneracy in such a way that the true ground state is unique and time-reversal invariant. Furthermore, it turns out that the magnitude of this effect may be tuned by a partial suppression of the magnetism (tunable edge magnetism).