Spin- and angle-resolved photoemission from ferromagnetic Fe(001)

For near-normal photoemission from ferromagnetic Fe(001) excited by linearly polarized synchrotron radiation, energy-resolved spin polarization and intensity distribution have been measured at 60 eV photon energy. Calculations using a one-step theory of photoemission consistently reproduce. the present spin-resolved data as well as earlier spin-averaged measurements. The quasi-particle exchange splitting deduced from the data is 2 eV. The agreement with band structure calculations is suggested to be coincidental due to a compensation of real and imaginary self-energy corrections.     

Inverse photoemission from Cu(001)

Bremsstrahlung ultraviolet spectra for Cu(001) are calculated for a photon energy ηω=9.7 eV within the framework of an inverse one-step model of photoemission for several angles of incidence of the electron beam. The comparison with recently reported experimental data shows that both the calculated energy dispersion of the peak in the spectra and the variation of the peak intensity are in reasonable agreement with the experiment.     

Chemisorption and surface ferromagnetism: Theoretical analysis of spin-resolved photoemission data from Ni(1 1 0)(2×1)−O

To extract information from recent experimental spin-resolved photoemission data from Ni(1 1 0)(2×1)?O, one-step theory calculations were performed for several geometrical and magnetic model structures. The observed strong influence of oxygen chemisorption on the normal photoemission spectra at room temperature is quantitatively reproduced assuming a (2×1) saw-tooth reconstruction with the third and fourth Ni layers magnetically dead, while the magnetization of the topmost two Ni layers is almost irrelevant for the spectra. It is concluded that bulk-like deeper layers are strongly quenched at least with regard to the near-X₂ exchange splitting.     

Theoretical study of spin-dependent bremsstrahlung from ferromagnetic Fe(110)

By means of a nonrelativistic one-step model Green function formalism of photoemission, spin-up- and spin-down-induced ultraviolet bremsstrahlung spectra have been calculated for ferromagnetic Fe(110) for several angles of incidence. Comparison with recent experimental data shows good agreement with regard to the existence and E(k_∥) despersion of both minority and majority spin features. Calculation of the corresponding bulk band structures and k_∥-resolved layer-by-layer quasi-particle densities of states permits a physical interpretation: most bremsstrahlung features can be understood in terms of bulk interband transitions, while one is due to surface resonance.     

Spectral density of states for ferromagnetic Fe (001) surface

We present a calculation for the spectral density of surface states at the (001) surface of ferromagnetic Fe. We employ the transfer matrix formalism for a model hamiltonian with a nine function basis ($\text{s, p}$ and $\text{d}$ orbitals). The results are presented at the special symmetry points Γ, X and M. There are bona fide surface states located above the Fermi level at point X.     

Growth of Fe films on Rh(001): a photoemission study

The growth mode and electronic structures of Fe thin films, epitaxially grown on Rh(001), were studied by various photoemission measurements for the film thickness of 0–12 monolayers. By comparing the valence band structures obtained from the angle-resolved photoemission spectra and the theoretical band calculations for the bulk Fe, we concluded that the valence band structure of the Fe film resembles that of fcc(001) in the low coverage region and that of bcc(110) in the high coverage region. This transformation of the electronic structure is considered to be related to the thickness dependence of the interlayer spacing of the films.     

High-resolution angle-resolved photoemission study of oxygen adsorbed Fe/MgO(001)

We have investigated the electronic states of clean Fe(001) and oxygen adsorbed Fe(001)–p(1 × 1)-O films epitaxially grown on MgO(001) substrates by means of polarization-dependent angle-resolved photoemission spectroscopy(ARPES)and extensive density-functional theory(DFT) calculations. The observed Fermi surfaces and band dispersions of pure Fe near the Fermi level were modified upon oxygen adsorption. By the detailed comparison of ARPES and DFT results of the oxygen adsorbed Fe surface, we have clarified the orbital-dependent p–d hybridization in the topmost and second Fe layers.Furthermore, the observed energy levels and Fermi wave numbers for the oxygen adsorbed Fe surface were deviated from the DFT calculations depending on the orbital characters and momentum directions, indicating an anisotropic interplay of the electron correlation and p–d hybridization effects in the surface region.     

Theory of spin-resolved photoemission from Fe at finite temperature: The disordered local moment picture

We present first principles calculations of the spin and angle-resolved photoemission spectra for Fe(100) at T = 0 and T = T_c, based on the KKRCPA treatment of the disordered local moment model. At T = 0 the calculations are in generally good agreement with experiment, and are shown to be quite sensitive to the surface potential and magnetisation. The high T calculations are also consistent with existing data, and a strong photon polarisation dependence is predicted as a consequence of the different exchange splitting of the T_2g and E_g states.     

Mechanisms of high-order perturbative photoemission from Cu(001)

We observed high-order 2- to 4-photon photoemission and above threshold photoemission (ATP) processes with 3.07 eV light from the Cu(001) surface. The intensity of 3-photon photoemission via excitation through the n = 1 image potential state significantly exceeded that of the 2-photon process. The ATP occurs either via single photon transitions from the image potential resonances above the vacuum level or by multiphoton transitions from image potential states below the vacuum level. The experimental ratio of the m- to (m + 1)-photon process yields is sensitive to the electronic band structure of the solid.     

Photon polarization effects in inverse photoemission from Cu(001)

A study of the polarization of Bremsstrahlung emitted from a Cu(001) single crystal surface helps to identify surface states and allows to determine the parity of bulk final states involved in a particular radiative transition if the angle of electron incidence is varied in a mirror plane of the crystal. In case of overlapping peaks with different polarization, a polarization dependent light detection increases in addition the apparent experimental resolution considerably.     

Electron escape effects in photoemission from Ag(001) surfaces

We have observed electron escape effects, separate from excitation probabilities, in photoemission from clean Ag(001) surfaces. By comparison of angle-resolved photoemission data for the (001) surface of silver at several photon energies with a direct transition model based on calculated band structures, we have determined the dispersion $\text{E}\text{(}\text{k}{}_{\mathrm{\perp }}\text{+}\text{k}{}_{\mathrm{\parallel }}\text{)}$ of final states involved in the photoemiss ion process. Observed photoelectrons from Ag(001) are emitted into a single final state band, closely parallelled by the $\text{G}{}_{\mathrm{\parallel }}\text{= 0}$ branch of the nearly-free-electron fcc band structure, even though other final states $\text{(}\text{G}{}_{\mathrm{\parallel }}\text{≠0)}$ are dipole-allowed. This is interpreted as the preferentially strong overlap of only one allowed final state band with states external to the crystal.     

Angle-resolved photoemission from CO on Fe(110)

We report normal emission, angle-resolved photoemission measurements of the system p (1×2)Co-Fe(110) at several photon energies. The lower bind-energy feature, commonly attributed to emission from both the 1π and 5σ molecular orbitals of CO, shifts from 6.9 to 8.1 eV (relative to the Fermi energy) as the photon energy is increased from 21 to 30 eV. We attribute this dispersion to a large variation in cross section for photoionization of the 1π- and 5σ-derived orbitals and use symmetry selection rules to Identify the 6.9 eV component as the 1π and the 8.1 eV component as the 5σ. This ordering is reversed from the gas phase ordering.     

Analysis of ferromagnetic order in Fe from x-ray photoemission and appearance potential spectroscopy

The total density of states has been calculated for 2000-atom cubic Fe clusters with local exchange fields, which vary randomly subject to assumed degrees of magnetic order. Comparison with X-ray photoemission and appearance potential data near the Curie temperature rules out a disordered-local-moment picture and suggests short-range ferromagnetic order extending over at least 4 Å up to about 6 or 7 Å.