Kondo impurity resonances for transition metal single atoms: orbital occupancy dependence.

E. C. GOLDBERG; F. FLORES

Mar del Plata, Argentina.

Congreso; • IV LASPM: Fourth Latin American Symposium on Scanning Probe Microscopy.; 2007

Scanning tunneling spectroscopy (STS) is a powerful technique for studying the local density of states (LDOS) around individual impurities adsorbed to metallic surfaces. By using STS, it has been found different LDOS features at low energy for elements having partially filled d orbitals [1]. Atoms near the middle of the 3d row such as V, Cr, Mn and Fe, show no discernible LDOS structure; while atoms near the ends of the row such as Ti, Co, and Ni show narrow resonances near the Fermi energy.             In order to understand the observed impurity trends while varying the d-orbital filling, we propose a theoretical formalism based on the use of projector operators to select the many-electron configurations within an Anderson-like description of the impurity-surface interaction. In this way, the process of removing an electron from (or adding an electron to) the impurity d orbital is taken into account by projecting the Anderson Hamiltonian over the corresponding electronic configurations with maximum value of total spin S. For instance, a transition from d5 to d4 involves the impurity atom electronic configurations with S=5/2 and S=2. The Green functions required for the calculation of the density of states at the impurity site, are solved by using the method of motion equations. Our results show more marked Kondo peak structures for atoms near the ends of the row. By considering in the case of Ti a d2 to d1 transition, while for Ni a d8 to d9 transition (d2 to d1 within a ‘hole’ picture), we reproduce qualitatively the experimental features observed in the LDOS for these both impurity atoms. [1] T. Jamneala, V. Madhavan, W. Chen, and M. F. Crommie, Phys. Rev. B61, 9990 (2000).