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TT: Tiefe Temperaturen
TT 34: Correlated Electrons - Quantum Impurities, Kondo Physics
TT 34.3: Talk
Wednesday, March 9, 2005, 10:15–10:30, TU H104
Spectral Properties and Spin Correlations in the 1D Kondo Box: a DMRG Study — •Th. Hand, J. Kroha, and H. Monien — Universität Bonn
For more than 20 years it has been a mystery why the spin-spin coupling between magnetic impurities embedded in a metal is in general short-ranged, despite the exponentially large spin coherence length ξ K = vF/TK induced by the impurity in the electron sea, with TK the Kondo temperature and vF = ℏ kF /m the Fermi velocity. Only recently it has been found by general physical arguments [1] and by perturbative calculations [2] that the relevant length scale is ℓ = (π ξ K/kFd−1)1/d, i.e. ℓ ≪ ξ K in dimensions d≥ 2. This suggests that in d=1 quantum wires long-range coupling between magnetic impurities can be achieved. In the present work we check this expectation by numerically exact density matrix renormalization group (DMRG) calculations, suitable for nanoscopic wires with discrete energy spectrum. Good quantitative agreement with the analytical predictions is found, including powerlaw behavior of the spin correlations for distance r<ℓ. We correlate the spin structure with Kondo features in the impurity spectrum and analyze their dependence on the parity of the electron number in the system (even/odd effect). The results may be relevant for recent experiments on carbon nanotubes and double quantum dot systems in the Kondo regime coupled through a bath with discrete spectrum.
[1] W. Thimm, J. Kroha, J. v. Delft, PRL 82, 2143 (1999).
[2] I. Affleck, P. Simon, PRL 86, 2854 (2001); P. Simon, I. Affleck, PRB PRB 68 115304 (2003).