Quantum interference phenomena in transport through molecules and multiple quantum dots [Elektronische Ressource] / Georg Begemann

In this thesis, we investigate electronic transport through molecular quantum dots weakly cou-pled to source and drain leads. To describe the electronic spectrum of the molecule that forms the quantum dot, the Pariser-Parr-Pople Hamil-tonian for conjugated molecules is introduced and adapted to the case of a benzene molecule. The generalized master equation (GME), which is the equation of motion for the reduced den-sity matrix (RDM), is used to calculate the current through the system and the conductance. Trans-port through a benzene molecule is investigated in two configurations, para- and meta configura-tion, which are defined by the lead molecule cou-pling. Interference between degenerate states leads to a suppression of the linear conductance when changing from the para to the meta con-figuration and to current blocking in the meta configuration for certain bias voltages. In pres-ence of parallel polarized ferromagnetic leads, Georg Begemannthis effect can be used to obtain control over the molecules net spin by all-electrical means. In the Quantum interference phenomena last chapter, cotunneling processes are described by means of an effective Kondo Hamiltonian, and in transport through molecules the results are compared to a theory which is ex-act to fourth order in the tunneling Hamiltonian.