Adatom-induced lateral inhomogeneity of quantum well states in metal multilayers

The influence of Co adatoms on the quantum well states (QWSs) existing in Cu/Co(100) multilayers is investigated by means of ab initio calculations. The typical oscillations of the density of states at the Fermi level as a function of the number of Cu layers are found to be strongly perturbed by the presence of adatoms on the surface. In a lateral direction, the QWSs exhibit atomic-scale variations, which depend on the number of Cu layers. These results suggest that the phase accumulation model, which is often used for analyzing QWS, is not sufficient to interpret electronic features near adatoms and call for experimental real-space investigations of QWS.

Figure 1

(Color online) Averaged DOS at $E_F$ for the top Cu layer as a function of the number of Cu layers $\left(N_{\text{Cu}}\right)$ in Cu/Co slabs obtained by ab initio calculations (solid lines) and fitting results using Eq. (1) (dashed lines). (a) Pure Cu slabs. (b) Cu slabs on a Co substrate. (c) Comparison of (a) (open circles) and (b) (closed circles). The data of (b) are offset by one layer along the abscissa and by $-0.018{\text{eV}}^{-1}$ along the ordinate. (d) Pure Cu slab covered by 1/4 ML of Co adatoms. (e) Cu slab covered by 1/4 ML of Co adatoms on a Co substrate. (f) Comparison of (d) (open circles) and (e) (closed circles). The data of (d) are offset by two layers along the abscissa and by $0.009{\text{eV}}^{-1}$ along the ordinate.

Figure 2

(Color online) (a) Atomic arrangement used for the calculations and naming convention of columns a–c and layer numbers. Left panels: top views of the Cu(100) layers at odd and even layer numbers. Right panel: side view of Cu layers, which corresponds to the dashed lines in the top views. (b) DOS as a function of energy at the atomic sites labeled in the inset. Inset: model of the surface of a slab of nine Cu layers $\left(N_{\text{Cu}}=9\right)$ with a 1/9 ML of Co adatoms on top.

Figure 3

(Color online) DOS at $E_F$ within columns a–c as a function of layer number. (a) $N_{\text{Cu}}=9$. (b) $N_{\text{Cu}}=7$. (c) DOS at $E_F$ averaged within each layer for $N_{\text{Cu}}=7,9$. DOSs at columns a–c are weight averaged according to their occupation numbers within a unit cell.