Transport through a Kondo quantum dot: Functional RG approach

We apply the functional renormalization group (FRG) method to calculate the conductance of a quantum dot in the Kondo regime. Starting from the exact FRG equations in Keldysh formulation for the Kondo exchange Hamiltonian in pseudo-fermion (pf) representation, we solve the coupled equations for the pf self energy and the coupling function, neglecting three-particle and higher correlation functions. The conductance G as a function of temperature T and bias voltage V is calculated using a renormalized Golden Rule expression. The limiting behavior at T and/or V >> T-K (T-K: Kondo temperature) agrees with known results. The difficulties when approaching strong coupling are analyzed and improvements are suggested. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim