Real time RG for the non-equlibrium Kondo model: Cutoffs set by voltage and decoherence

Thomas Korb

Institut fuer Theoretische Physik A, RWTH Aachen

While the Kondo effect in equilibrium is well understood there is known less for the Kondo effect in non-equilibrium. Especially the question was raised, if a finite voltage and current induced decoherence prevents the system from going into the strong coupling limit for $V>T_K$ and how to calculate the $I-V$ [1,2]. In [2] a perturbative RG for the scaling of the verticies in non-equilibrium was developed, but the decoherence was included only on the basis of a perturbation calculation. A different approach was used in [3], where a flow equation analysis was performed on the expense to reside on a Hamiltonian description for the non-equilibrium. There it was found, that the scaling is cutted by balancing of second and third order contributions in the flow equations. We use the real time RG formalism developed in [4] to analyze the non-equilibrium Kondo effect. It is demonstrated how the cutoffs set by voltage and decoherence rate emerge naturally from a closed set of RG equations on the Keldysh contour (including dephasing of nondiagonal elements of the density matrix). Therefore we are able to calculate the $I-V$ characteristic for $V>T_K$ within one scheme and within a full nonequilibrium formalism. [1] P. Coleman, C. Hooley, and O. Parcollet, Phys. Rev. Lett. 86, 4088 (2001). [2] A. Rosch, J. Kroha, and P. W\"olfle, Phys. Rev. Lett. 90, 076804 (2003). [3] S. Kehrein, Phys. Rev. Lett. 95, 056602 (2005). [4] H. Schoeller and J. K\"onig, Phys. Rev. Lett. 84, 3686 (2000).