Spectral characteristics induced by a single impurity in a two-dimensional system

Abstract

A single substitutional impurity in a two-dimensional electron system is studied on the basis of the hybrid Anderson model with s-d coupling only between neighbouring sites. Analytic expressions for local densities of states (DOS) for the impurity d orbitals, d(z2) and d(x2-y2), and for the s orbitals at the impurity and neighbouring host sites are determined. Special emphasis is put on the appearance of the well-defined resonance states and the antiresonance dips in the spectra, which are discussed in connection with the Fano phenomena. In contrast to the simple s-d Anderson model with the on-site coupling, it is demonstrated that the sharp resonance can be formed by increasing the coupling between the impurity and the host system, and that the resonance energy is shifted towards the band centre where the Van Hove singularity of the host DOS is present.