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TT: Fachverband Tiefe Temperaturen

TT 4: CE: Quantum Impurities, Kondo Physics

TT 4.9: Vortrag

Montag, 22. März 2010, 12:30–12:45, H21

Nonequilibrium functional RG with frequency dependent vertex function – a study of the single impurity Anderson model — •Severin Jakobs^{1, 2}, Mikhail Pletyukhov^{1, 2}, and Herbert Schoeller^{1, 2} — ¹Institut für Theoretische Physik A, RWTH Aachen University, D-52056 Aachen, Germany — ²JARA – Fundamentals of Future Information Technologies, Germany

We investigate nonequilibrium properties of the single impurity Anderson model by means of the functional renormalization group (fRG) within Keldysh formalism. We present how the level broadening Γ/2 can be used as flow parameter for the fRG. This choice preserves important aspects of the Fermi liquid behaviour that the model exhibits in case of particle-hole symmetry. An approximation scheme for the Keldysh fRG is developed which accounts for the frequency dependence of the two-particle vertex in a way similar but not equivalent to a recently published approximation to the equilibrium Matsubara fRG. Our method turns out to be a rather flexible tool for the study of weak to intermediate on-site interactions U≲ 3Γ. In equilibrium we find excellent agreement with NRG results for the linear conductance at finite gate voltage, magnetic field, and temperature. In nonequilibrium, our results for the current agree well with TD-DMRG. For the nonlinear conductance as function of the bias voltage, we propose reliable results at finite magnetic field and finite temperature. Furthermore, we demonstrate the exponentially small scale of the Kondo temperature to appear in the second order derivative of the self-energy.