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HL: Halbleiterphysik

HL 2: Symposium: Kondo Physics in Quantum Dots

HL 2.5: Fachvortrag

Monday, March 26, 2001, 12:30–13:00, S2

Numerical RG analysis of interacting quantum dots — •Walter Hofstetter — Theoretische Physik III, Universität Augsburg, 86135 Augsburg

Wilson’s Numerical Renormalization Group (NRG) is so far the only nonperturbative method that can reliably access low–energy properties of quantum impurity systems. We present a recent extension of the method, the DM–NRG [1], which yields highly accurate results for dynamical quantities at arbitrary frequencies and temperatures. As an application, we determine the spectrum and the magnetoconductance of a quantum dot in an external magnetic field.

Furthermore, we discuss magnetic impurities with orbital degeneracy [2], which have been inferred in recent experiments on quantum dots in an Aharonov-Bohm geometry. It is demonstrated that for spinless electrons, interference between neighbouring levels sets the low–energy scale of the system. However, switching on an external field leads to a remarkable crossover into a regime dominated by Kondo screening.

A more realistic model including the electron spin is studied within an extended two-band NRG procedure. We observe competition between interference and Kondo screening, similar to the situation in two-impurity models (RKKY). Both effects can be observed in the single–particle spectrum of the dot as well as in the linear conductance. In addition, we predict that the broadening–induced level splitting should be clearly visible in measurements of the optical absorption power.

[1] W. Hofstetter, Phys. Rev. Lett. 85, 1508 (2000).

[2] D. Boese, W. Hofstetter, and H. Schoeller, cond-mat/0010250.