Spin-Dependent Transport in Graphene Nanostructures

Graphene, a two-dimensional material consisting of carbon atoms arranged in a honeycomb lattice, has become famous for the evidence that its electronic structure approximately corresponds to the one of massless Dirac fermions. However, in order to correctly describe graphene, the spin, which plays an essential role in the physics of Dirac fermions, has to be replaced by the so-called pseudospin, an intrinsic property of the honeycomb lattice which is not related to the electrons’ real spin. If, now, the real spin is considered, too, the effective Hamiltonian has to be extended by terms which have no equivalents in the original Dirac Hamiltonian. While charge transport properties can be predicted from Dirac physics very realiably, the extended Hamiltonian leads to new phenomena in the context of spin transport. In this thesis two distinct topics are investigated theoretically. The presented results are mainly based on numerical simulations using a recursive Green’s function algorithm. The first part of this thesis covers spin relaxation in graphene. Different sources of spin relaxation are investigated with a particular focus on the role of locally varying spin-orbit coupling and adatoms. The second part covers edge magnetism in graphene zigzag nanoribbons. It is shown how magnetic clusters form even in the presence of a potential which is not homogeneous in space. Different signatures of zigzag edge magnetization on charge and spin transport are presented.