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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 $V$ $\gg T_{K}$ ($T_{K}$ : Kondo temperature) agrees with known results. The difficulties when approaching strong coupling are analyzed and improvements are suggested.