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Kondo screening by the surface modes of a strong topological insulator

We consider a magnetic impurity deposited on the surface of a strong topological insulator and interacting with the surface modes by a Kondo exchange interaction. Taking into account the warping of the Fermi line of the surface modes, we derive a mapping to an effective one dimensional model and show that the impurity is fully screened by the surface electrons except when the Fermi level lies exactly at the Dirac point. Using an Abrikosov fermion mean-field theory, we calculate the shape of the electronic density Friedel oscillation resulting from the presence of the Kondo screening cloud. We analyze quantitatively the observability of a six-fold symmetry in the Friedel oscillations for two prototype compounds: Bi$_2$Se$_3$ and Bi$_2$Te$_3$.