# Dresden 2006 – wissenschaftliches Programm

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# TT: Tiefe Temperaturen

## TT 4: Correlated Electrons: Quantum Impurities, Kondo Physics

### TT 4.1: Hauptvortrag

### Montag, 27. März 2006, 11:00–11:30, HSZ 301

**Current vs. Correlations: The Nonequilibrium Kondo Model** — •Stefan Kehrein — LMU München, Department für Physik

Quantum dot experiments show new aspects of electron correlation physics that are inaccessible in bulk materials. One example is the realization of out-of-equilibrium situations far beyond the linear response regime. Such quantum many-body systems far away from equilibrium are theoretically not well-understood and are beginning to emerge as an exciting new frontier in quantum many-body physics. In this talk we examine the Kondo model as a paradigm for correlated impurity physics. While its equilibrium ground state with Kondo screening due to the formation of a many-body bound state is well-understood, much less is known about the steady state that develops when a constant voltage bias is applied across the impurity. In particular, the coherent Kondo screening processes turn out to be in competition with current-induced decoherence, and this competition determines the phase diagram of the nonequilibrium Kondo model. We will discuss various physical observables like the dynamic and static spin susceptibility and the T-matrix to get insights into this nonequilibrium steady state and to compare it with finite temperature equilibrium states. We will also see how the method of infinitesimal unitary transformations (flow equation method) serves as a suitable generalization of scaling concepts to such nonequilibrium situations [1].

[1] S. Kehrein, Phys. Rev. Lett. **95**, 056602 (2005)