Spin-transport and spin-coherence in quantum wires and quantum dots, carbon nanotubes and graphene, spin-orbit interaction

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Topic of this project is the influence of spin-dependent interactions on transport properties of quantum dots, one-dimensional (1d) quantum wires and quantum spin chains. The project is divided in three subparts: A) We will study the interplay of spin and orbital degrees of freedom in multi-level dots, where spin-orbit interaction (SOI) or cotunnelling processes lead to spin-dependent interactions. This includes the study of the Dzyaloshinskii-Moriya interaction, spin-polarized currents in ring structures, the competition between Kondo and RKKY correlations, and the influence of frequency-dependent lead density of states for graphene-based devices. B) We will calculate the complete dynamics of an itinerant spin prepared in a nonequilibrium state in a quantum wire in the presence of SOI and electron-phonon coupling. From the spin dynamics characteristic spin relaxation and spin decoherence times will be extracted. C) We plan to calculate the spin conductivity in a low-energy field theory of the spin-1 Haldane chain. The aim is to clarify a discrepancy between semi-classical and full quantum field theoretical treatments as to what extent the spin conductivity possesses a regular part within the gap. The three sub-projects are in close relation to the experimental projects as well as the theoretical project of this Research Unit. For sub-project A we will use nonequilibrium renormalization group (RG) methods developed recently in our groups, whereas sub-projects B and C will be performed using standard bosonization and field-theoretical techniques.