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TT: Fachverband Tiefe Temperaturen
TT 44: Poster Session Correlated Electrons
TT 44.2: Poster
Donnerstag, 17. März 2011, 10:00–13:00, P1
Real-space Kondo correlations — •Michael Becker, Andrew Mitchell, and Ralf Bulla — Universität zu Köln
We investigate real-space Kondo correlations in various impurity models. Any physical quantity in real space can be calculated from purely local impurity correlators. In the simplest (but most revealing) example of the Anderson model, the density variation around the impurity is related to the impurity Green function, which we calculate accurately via the numerical renormalization group technique. Signatures of the ‘free orbital’, ‘local moment’ and ‘strong coupling’ fixed points are evident in real space, with characteristic length scales RFO and RLM being associated with each at T=0. The ‘local moment cloud’ is an exponentially extended object with RLM∼ 1/TK; Kondo screening itself occurring for r ≫ RLM. As the temperature is increased, the Kondo effect is destroyed, as manifest in real space by the divergence of RLM, implying that the uncompensated moment due to the impurity becomes infinitely extended. The familiar RG picture known for other classic models is similarly apparent in real space. In particular, the phase transition in the pseudogap Anderson model (realised here for an impurity in graphene) is associated with a diverging length scale; and the existence of both ’local moment’ and ’overscreening’ clouds are demonstrated in the two-channel Kondo model.