Correlated electron systems with antiferromagnetic spin interaction

In the first part of this thesis we extend and apply the functional renormalization group method to the nonequilibrium Kondo dot model. The main emphasis is based on the question how decoherence rates are incorporated in a systematic way in a renormalization group procedure. Further we calculate the conductance through the Kondo dot. In the second part we develop and single out a spin wave theory to describe spin-stripes in certain high-TC copper oxide compounds