Surface state with $d_{z^2}$ symmetry at Y(0001): A combined direct and inverse photoemission study

A surface state of $d_{z^2}$ symmetry is identified on Y(0001) at about 0.1 eV above the Fermi level by a combined direct and inverse photoemission experiment. The spectral signatures of this surface state appear on both sides of the Fermi level and are equally quenched upon the formation of a surface monoxide. Concurrently, a new interface state appears at $-0.7\text{eV}$ and spectral intensity remains at 0.6 eV, which is attributed to transitions into bulk bands at the gap edge. This detailed analysis of the surface electronic structure gains in importance when applied to Gd(0001), which is isoelectronic to yttrium with respect to the valence electrons but ferromagnetic with exchange-split bands owing to the additional half-filled $4f$ shell.

Figure 1

(Color online) (a) Color-inverted LEED image $\left(E_{\text{kin}}=42\text{eV}\right)$ and (b) STM image $\left(500\times 500{\text{nm}}^2\right)$ of the Y(0001) surface.

Figure 2

Surface electronic structure of Y(0001) as measured by PE (left) and IPE (right). The spectral features are attributed to a surface state $\left({\text{SS}}_{\text{PE}},{\text{SS}}_{\text{IPE}}\right)$, to bulk states $\left({\text{B}}_1,{\text{B}}_2,{\text{B}}_3\right)$, and to impurity-related states (${\text{O}}_2$, H).

Figure 3

Angle-resolved PE and IPE spectra for the Y(0001) surface along $\overline{\Gamma }\overline{\text{K}}$. ${\text{SS}}_{\text{PE}}$ and ${\text{SS}}_{\text{IPE}}$ are weakly dispersing features.

Figure 4

PE and IPE spectra of Y(0001) as a function of film roughness. The film roughness was tuned by altering the annealing temperature $T_{\text{A}}=950\text{K}$ (black) and 293 K (light gray) during preparation.

Figure 5

PE and IPE spectra for the clean Y(0001) surface (light gray) and after oxygen exposure [0.25 L (gray) and 0.5 L (black)]. Thick lines represent simulations of the spectra with the following components shown as thin lines: Lorentzian states $L_1$ ($E_{L_1}=0.13\text{eV}$ and ${\Gamma }_{L_1}=0.3\text{eV}$), $L_2$ ($E_{L_2}=0.6\text{eV}$ and ${\Gamma }_{L_2}=0.4\text{eV}$), and background $B$.