Figure 1

(a) Schematic view of a trilayer sample. The $\sqrt{3}\times \sqrt{3}R30°$ Bi-Ag alloy is grown on a Ag buffer—whose thickness can be varied—deposited on a silicon substrate. (b) First Brillouin zones of the surface structures. The symmetry lines $\overline{\Gamma }\overline{K}\overline{M}$ and $\overline{\Gamma }{\overline{K}}^{\prime }{\overline{M}}^{\prime }$ refer to Si(111) and to the alloy, respectively. (c) ARPES intensity of the surface states of a Bi-Ag alloy grown on a thick Ag layer deposited on Si(111) along $\overline{\Gamma }{\overline{K}}^{\prime }{\overline{M}}^{\prime }$. This system is similar to the alloy grown on a Ag(111) single crystal. Dashed lines indicate the branches of opposite spins of the $s{p}_z$ surface state. Arrows point out bands of $p_x{p}_y$ symmetry. Close to $\overline{\Gamma }$ all bands exhibit a rotational symmetry around the surface normal.Reuse & Permissions

Figure 2

(a) Raw ARPES data along $\overline{\Gamma }\overline{K}$ at 55 K. QWS’s in a 17 ML bare Ag buffer deposited on Si(111). These parabolic states are numbered $\nu =1\dots n$. Kinks in the dispersion (arrow) are due to the hybridization of the QWS with the $p$ bands of silicon. SS stands for the Shockley surface state of Ag(111). (b) EDC extracted from Fig. 2a at $\overline{\Gamma }$, i.e., $k=0.0{\AA }^{-1}$. The 1st and 2nd QWS signatures and the SS are indicated. (c) MDC extracted from Fig. 2a at $-300\mathrm{meV}$ shows the successive branches of the QWS. (d) Raw ARPES intensity along $\overline{\Gamma }{\overline{M}}^{\prime }$ at 55 K of the Bi-Ag alloy grown on 17 ML of Ag. (e) EDC extracted from Fig. 2d for $k=0.20{\AA }^{-1}$ and $k=0.25{\AA }^{-1}$. Arrows indicate gaps of 100–200 meV in the dispersion of the $p_x{p}_y$ bands.Reuse & Permissions

Figure 3

(a),(b), and (c) second derivative of the ARPES intensity along $\overline{\Gamma }{\overline{M}}^{\prime }$ for three alloy-covered samples at RT with different Ag film thicknesses, respectively, 19, 16, and 10 ML. Circles correspond to MDC fits of the QWS observed on the bare Ag thin films of the corresponding thicknesses shifted by 50–150 meV upwards in order to match the remaining parts of the QWS at large $k$ values after Bi deposition (e.g., red arrows).Reuse & Permissions

Figure 4

Effect of QWS’s on the spin-split electronic structure of the $\mathrm{Bi}/\mathrm{Ag}$ surface alloy, as obtained from first-principles electronic-structure calculations. (a)–(c): The spectral density at the Bi site is displayed as gray scale (with white indicating vanishing spectral weight) for $\mathrm{BiAg}/\mathrm{Ag}(111)$ (a) and $\mathrm{BiAg}/\mathrm{Ag}/\mathrm{Si}(111)$ for Ag buffer thicknesses $d=10$ (b) and $d=19$ (c). The wave vector is chosen as in the experiment (Fig. 3). (d)–(f): The spin polarization of the electronic states is visualized by $\Delta N(E,{\mathbf{k}}_{\parallel })$, i.e., the difference of the spin-up and the spin-down spectral density. White and black indicate positive and negative values, respectively, where gray is for zero $\Delta N$.Reuse & Permissions