Regensburg 2010 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 10: Poster I
MA 10.35: Poster
Dienstag, 23. März 2010, 10:45–13:45, Poster A
Single or multichannel Kondo effect in graphene — •Zhen-Gang Zhu1, Kai-He Ding2, and Jamal Berakdar1 — 1Institut für Physik, Martin-Luther Universität Halle-Wittenberg, Heinrich-Damerow-Straße 4 06120 Halle, Germany — 2Department of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410076, China
Dynamic screening in a Kondo system may compensate or over compensate for the localized magnetic moment signifying respectively a Fermi or a non-Fermi liquid ground state. The former (latter) case occurs in one (two) channel Kondo effect with a magnetic impurity having spin 1/2. We investigate this issue in graphene starting from the tight-binding Anderson model. Schrieffer-Wolff transformation is performed to derive the Kondo model. To verify our findings, we also conduct direct computations by considering the two-body interaction explicitly. At last, the Kondo temperature is calculated from Anderson model in the large U limit. We find: i) for nearest neighbor hopping, a two-channel Kondo character is present when the impurity is symmetrically coupled to the A and B sublattice; otherwise a single channel Kondo is realized. ii) The exchange interaction coefficient for one channel is vanishing when the spin is symmetrically coupled to the spanned sublattice to this channel in absence of a gate voltage. However it is finite in the presence of a gate voltage. iii) The degeneracy of the two Dirac points leads only to a higher Kondo temperature which is increasing exponentially with increasing gate voltage. We point out the experimental feasibility by varying a gate voltage.
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