- Agnieszka L. Kozub: Magnetic impurities in bulk copper and on graphene
- 9. 3. 2016, 14:50
- lecture room F2, first floor Ke Karlovu 5
- more information
Abstract:
The electronic structure of impurity atoms with partially filled d or f shells will be discussed. To study the electron correlations in these systems, we use a method that combines the density functional theory in a local density approximation with an exact diagonalization of the discretized multi-orbital Anderson impurity model (DFT+ED).
We start with applying our approach to the transitional metal impurities in the bulk. For a cobalt atom located in bulk copper, the calculations yield the nonmagnetic singlet ground state. The local moment at the Co atom is screened by the bath of conduction electrons. The calculations suggest the formation of the muli-orbital Kondo-like singlet for the Co atom in bulk Cu. The computed spectral densities are in a good agreement with those obtained using the quantum Monte Carlo method [1,2].
Next we consider the selected rare-earth adatoms adsorbed on graphene. These studies are important
for the scanning tunneling spectroscopy experiments. The combined effect of electron correlations and spin-orbital coupling is illustrated on samarium and neodymium atoms adsorbed on graphene. The LDA+U method predicts both these adatoms to carry a local magnetic moment (spin as well as orbital). This is expected for Nd but not for Sm which has a non-magnetic f6 (J=0) ground state configuration as a free atom, and the weak bonding to graphene is not expected to substantially change this ground state. The more accurate method employing the Anderson impurity model cures this problem and yields the anticipated non-magnetic ground state with nf=6 and J=0 for the Sm adatom. The Nd adatom remains magnetic with nf=3.7 and J=4.2.
[1] B. Surer, M. Troyer, P. Werner, T.O. Wehling, A.M. Läuchli, A. Wilhelm, and A.I. Lichtenstein, Phys. Rev. B 85, 085114 (2012).
[2] A. L. Kozub, J. Kolorenč, and A. B. Shick, in WDS'15 Proceedings of Contributed Papers — Physics (eds. J. Safrankova and J. Pavlu), Prague, Matfyzpress, pp. 48–53 (2015).