Figure 1

(left) Possible two-photon photoemission processes. (right) Experimental geometry showing a sample with the gold chains and step edges oriented perpendicular to the plane of incidence; i.e., the mirror plane is in the plane of incidence. In situ azimuthal rotation of the sample by 90${}^{\circ }$ allows measurement of the dispersion along the step edges.Reuse & Permissions

Figure 2

LEED image of Si(553)-Au with faint half- and third-order horizontal streaks indicating the reconstruction of the gold chains and step-edge atoms, respectively. The $(1\times 1)$ unit cell of the Si substrate is outlined in red.Reuse & Permissions

Figure 3

Polarization-dependent 1PPE spectra recorded with $6.2$-eV photons in normal emission for the mirror plane oriented parallel (dashed curves) and perpendicular (solid curves) to the plane of incidence (cf. Fig. 1). The peaks labeled B (D) represent occupied states that are even (odd) with respect to the mirror plane (cf. Fig. 1).Reuse & Permissions

Figure 4

Photoemission intensity maps ($h\nu =6.2$ eV) for azimuthal orientations and polarizations showing the downward-dispersing peak D (cf. Fig. 3). In the $\overline{\Gamma K}$ direction the bands assigned to the Au chains can be seen. Their Fermi-level crossings are marked.Reuse & Permissions

Figure 5

Photoemission intensity maps in opposite azimuthal directions ($\overline{\Gamma M}$ and $\overline{\Gamma M^{\prime }}$) obtained with $p$-polarized 6.2-eV photons incident in the mirror plane. The lack of mirror symmetry shows that peak B represents a bulk transition.Reuse & Permissions

Figure 6

The 2PPE spectra recorded in normal emission for all polarization combinations of IR and UV photons and for the mirror plane oriented parallel (dashed curves) and perpendicular (solid curves) to the plane of incidence (cf. Fig. 1).Reuse & Permissions

Figure 7

Dispersion of the image-potential resonance C parallel and perpendicular to the mirror plane. Data were taken with a time delay of 50 fs between the $p$-polarized UV-pump and IR-probe pulses to enhance the relative intensity of the image-potential resonance. Along $\overline{\Gamma M^{\prime }}$ the intensity above 0.7 eV is enhanced to show the image-potential resonance more clearly.Reuse & Permissions

Figure 8

Photoemission spectra in normal emission with the time delay negative (left, UV before IR) and positive (right, IR before UV). The mirror plane is oriented perpendicular to the plane of incidence (see Fig. 1). All spectra are recorded for both pulses $p$ polarized.Reuse & Permissions

Figure 9

Time-resolved 2PPE intensity of peak A for both pulses being $p$ polarized. The spectrum shows intensity for negative (UV before IR) and positive (IR before UV) time delays, which indicates an UV-pump IR-probe and an IR-probe UV-pump process, respectively. For positive time delays the decay exhibits two decay constants of 125 and $>$600 fs.Reuse & Permissions

Figure 10

Energy diagram of the observed 2PPE transitions at normal emission. The energies of the intermediate states are referenced to the vacuum level for $3h\nu$-$1h\nu$ processes and to the Fermi energy for $1h\nu$-$3h\nu$ processes.Reuse & Permissions

Figure 11

(a) Comparison between theoretical band structure of Si(553)-Au and three states detected experimentally by 2PPE. Colored symbols correspond to the colored atoms in the structural model shown in (b). Yellow circles are bonding (lower) and antibonding (upper) states from the Au chains, red diamonds are exchange-split states from spin-polarized Si atoms at the step edge, green diamonds are states from nonpolarized Si step-edge atoms, and green circles are states from nonpolarized Si atoms on the opposite side of the honeycomb chain. The zone boundary (ZB) is that of the 1$\times$1 unit cell. Because the actual cell is a 1$\times$3 cell (we used a ferromagnetic array of polarized Si atoms rather than the full 1$\times$6 antiferromagnetic array of Ref. 7), we unfolded the 1$\times$3 Au bands into the 1$\times$1 cell for easier visualization.Reuse & Permissions