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We have investigated the electronic structure of the commensurate charge-density-wave (CDW) phase for $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$ by Ta $4f$ core-level and the angle-resolved photoemission. From the energy shifts of Ta $4f$ core levels due to a CDW formation, it is found that the CDW amplitude in the $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$ is smaller than that in $1T\ensuremath{-}{\mathrm{TaS}}_{2}$ reported previously. The band dispersion along the normal to the two-dimensional layers indicates that $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$ has a three-dimensional (3D) character in the Fermi surface compared with $1T\ensuremath{-}{\mathrm{TaS}}_{2},$ which has a two-dimensional Fermi surface. The 3D Fermi surface of $1T\ensuremath{-}{\mathrm{TaSe}}_{2}$ is thought to originate from the larger interaction between layers due to a large charge transfer between Ta $5d$ and Se $4p$ orbitals.

We have investigated the electronic structure of ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ by photoemission spectroscopy and band-structure calculations within the local-density $\mathrm{approximation}+U$ $(\mathrm{LDA}+U)$ scheme. In valence-band photoemission spectra, a distinct double-peak feature has been observed near the Fermi level ${(E}_{F}).$ A photon-energy dependence of the spectra and the $\mathrm{LDA}+U$ band-structure calculation have revealed that the first peak crossing ${E}_{F}$ consists of the (Fe+Mo) ${t}_{2g\ensuremath{\downarrow}}$ states and the second peak well below ${E}_{F}$ is dominated by the Fe ${e}_{g\ensuremath{\uparrow}}$ states. This clearly shows that only the down-spin states contribute to the ${E}_{F}$ intensity, thus the half-metallic density of states (DOS) is realized. We point out that the observed half-metallic DOS can be attributed to the strong Hund's rule energy stabilization due to the high-spin ${3d}^{5}$ configuration at the Fe site.

We present high resolution angle resolved photoemission data of the bilayer superconductor ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ (Bi2212) showing a clear doubling of the near ${E}_{F}$ bands. This splitting approaches zero along the $(0,0)\ensuremath{\rightarrow}(\ensuremath{\pi},\ensuremath{\pi})$ nodal line and is not observed in single layer ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Cu}{\mathrm{O}}_{6+\ensuremath{\delta}}$ (Bi2201), indicating that the splitting is due to the long sought after bilayer splitting effect. The splitting has a magnitude of approximately 75 meV near the middle of the zone, extrapolating to about 110 meV near the $(\ensuremath{\pi},0)$ point. The existence of these two bands also helps to clear up the recent controversy concerning the topology of the Fermi surface.

We have investigated the electronic structure of K 0.5 CoO 2 in the metallic phase by high-resolution angle-resolved photoemission spectroscopy at a low temperature. An observed Fermi surface of K 0.5 CoO 2 was a large hexagonal one around the Γ point only, with no hole pockets on the Γ – K lines which was typically predicted by band-structure calculations with local-density approximation (LDA). We also found that a modulation of the Fermi velocity, which was the largest at K point and the smallest at M point, was again opposite to the prediction by LDA band-theory. In spite of this conflicting with LDA band-theory, our results are both in agreement with what was observed in Na x CoO 2 .

Angle-resolved photoemission results from Nd 2-x Ce x CuO 4 (001) single-crystal thin films are reported. The valence-band spectra show a resolution-limited Fermi edge and can be compared to the band calculation to a fair degree, though the main peaks exhibits less well defined dispersion of less than 0.4 eV. A bandlike state of dominant C u 3d character is found just below the Fermi level. It shows well-defined but small dispersion of ∼0.2 eV. There is a possibility of Kondo-type renormalized heavy-electron band formation at the Fermi level.

High-resolution angle-resolved photoemission study of the surface state in ferromagnetic Ni(1 1 1) has been performed to evaluate the strength of many-body interactions. We could not observe a kink structure in the energy band dispersion derived from the electron–phonon interaction. The imaginary part of the self-energy was evaluated; it increases significantly with increasing energy, indicating a strong electron–electron interaction.

High-resolution angle-resolved photoemission study of Pd(1 1 0) single crystal has been done to evaluate the strength of electron–phonon interaction. We found a clear kink structure in the energy-band dispersion at E ∼ - 30 meV , which corresponds well to the energy scale of the Debye temperature. The obtained real part of the self-energy has been explained well by the self-energy due to the electron–phonon interaction. We have evaluated the electron–phonon coupling constant λ = 0.41 ± 0.03 for the s-like Fermi surface around the Γ point.

High-resolution low-temperature angle-resolved photoemission spectroscopy of Fe(1 1 0) single crystal has been done to evaluate many-body interactions on the quasi-particles at the Fermi level. A kink structure in the minority-spin band (B↓) on the Fermi surface (FS) around the Γ point has been clearly observed at the binding energy of ∼40 meV, but it is absent for the majority-spin band (B↑) on the FS around the Γ point. Additional spectral feature has been observed for B↑, indicating a coexistence of a surface resonance state. By the analyzes of the imaginary part of the self-energy, we have confirmed that the kink structure is derived from the electron–phonon interaction.

Unoccupied electronic structure of iron-based superconductors NdFeAsO0.7 (Tc=51 K), BaFe2As2 and Ba(Fe0.89Co0.11)2As2 (Tc=23 K) has been investigated by means of inverse-photoemission spectroscopy (IPES). The unoccupied Fe 3d states are observed around 1 eV above the Fermi level for all compounds. The Fe 3p-3d resonant IPES suggests that the unoccupied Fe 3d states of Ba(Fe1−xCox)2As2 have more localized character compared with those of NdFeAsO0.7. The unoccupied Nd 4f states of NdFeAsO0.7 are located around 5 and 7 eV, and the Ba 5d and Ba 4f states of Ba(Fe1−xCox)2As2 are located around 5 and 12 eV, respectively.

We have characterized the electronic structure of FeSe1-x Te x for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (EF): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near EF and approximately 6 eV above EF; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near EF for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe.

The electronic structure of reduced SrTiO3(110) surface prepared by annealing in ultrahigh vacuum (UHV), has been studied using photoemission spectroscopy (PES) and scanning tunneling microscopy/spectroscopy (STM/STS). In the photoemission spectra of reduced SrTiO3(110) surface after annealing in UHV at 800°C, a clear metallic state with a sharp Fermi cut-off and a broad state centered at ∼1.1eV below the Fermi level are observed in the band gap region. A Ti3p->3d resonance enhancement is occurred for the metallic state, but not for the ∼1.1eV state. On the other hand, after the sample was annealed in UHV at 1000°C, it has been shown that the metallic state becomes drastically weak, and that only the ∼1.1eV state is seen in the band gap region. Thereafter, the ∼1.1eV state exhibits a clear Ti3p->3d resonance enhancement. The difference in the spectral feature of these band gap states is directly related to the surface geometric structural change.

We examined the dimensionless coupling parameters of many-body interactions for a free-electron-like surface-derived state in Al(100) by means of high-resolution angle-resolved photoemission spectroscopy. A kink structure was found to exist in the energy-band dispersion near the Fermi level (${E}_{F}$), which was attributed to the electron-phonon interaction. At 50 K, the coupling parameters of the electron-phonon and electron-electron interactions were estimated as ${\ensuremath{\lambda}}_{ep}=0.67\ifmmode\pm\else\textpm\fi{}0.05$ and ${\ensuremath{\lambda}}_{ee}\ensuremath{\sim}0.003$, respectively, indicating that the effective mass enhancement was mainly derived from the electron-phonon interaction. The temperature dependence of the kink structure, as measured by ${\ensuremath{\lambda}}_{ep}(T)$, was consistent with a theoretical calculation based on the Eliashberg function. A quasiparticle peak with a width of $15--20$ meV was found near ${E}_{F}$, which was explained well by the simulated spectral function incorporating the self-energy evaluated in this study. We found that the electrons at the surface were strongly scattered by the defects at the surface and that the linewidth was significantly broadened (${\ensuremath{\Gamma}}_{0}=0.238\ifmmode\pm\else\textpm\fi{}0.006$ eV).

Phenomenological model calculations of Sr 2 RuO 4 show that the marked enhancement of the hybridization between the two-dimensional d x y band and one-dimensional d y z , z x bands is caused by the Coulomb and spin–orbit interactions. Owing to the enhanced hybridization effect, the van Hove singularity (vHS) of the γ band in the vicinity of M decreases to about 40 meV above the Fermi level ( E F ). Moreover, the vHS approaches E F owing to the electron–phonon interaction (EPI). A few peculiar phonon modes interacting with the one-dimensional orbital component via the vHS can mediate the p -wave paring in Sr 2 RuO 4 .

Angle-resolved photoemission from Fe(110) reveals spin-orbit splitting of the ${\mathrm{\ensuremath{\Gamma}}}_{25}^{\ensuremath{'}}$\ensuremath{\downarrow} state into ${\mathrm{\ensuremath{\Gamma}}}_{7}^{+}$ and ${\mathrm{\ensuremath{\Gamma}}}_{8}^{+}$ components, separated by 110\ifmmode\pm\else\textpm\fi{}10 meV, which is much larger than the theoretical estimate (\ensuremath{\sim}45 meV). Critical points at \ensuremath{\Gamma} for relativistic bands (nonrelativistic labels in parentheses) are measured as E(${7}^{+}$ (25\ensuremath{'})\ensuremath{\downarrow})=-0.27 eV, E(${8}^{+}$ (25\ensuremath{'})\ensuremath{\downarrow})=-0.39 eV, E(${8}^{+}$ (12)\ensuremath{\uparrow})=-0.76 eV, E(${7}^{+}$+${8}^{+}$ (25\ensuremath{'})\ensuremath{\uparrow})=-2.7 eV, and E(${6}^{+}$ (1)\ensuremath{\uparrow}\ensuremath{\downarrow})=-7.5 eV. These findings show the importance of spin-orbit effects in the band structure of Fe, not adequately accounted for in existing calculations.

The possibility that a pairing boson might act as the 'glue' to bind electrons into a Cooper pair in superconductors with a high critical temperature (T(c)) is being actively pursued in condensed-matter physics. Gweon et al. claim that there is a large and unusual oxygen-isotope effect on the electronic structure, indicating that phonons have a special importance in high-temperature superconductors. However, we are unable to detect this unusual oxygen-isotope effect in new data collected under almost identical material and experimental conditions. Our findings point towards a more conventional influence of phonons in these materials.

Quasiparticle spectra of the Ca1−xSrxVO3 and Sr2RuO4 single-crystals are reported. The spectra have been measured around 14K for Ca1−xSrxVO3 and 80K for Sr2RuO4 by high-resolution angle-integrated photoemission spectroscopy. Large spectral weight redistribution has been observed in both systems, suggesting an importance of the electron correlation.

Effect of doping electrons on the electronic structure of single-crystalline LaxSr1−xTiO3 samplex (x=0.001, 0.01, 0.05) has been studied for the fractured surface by ultraviolet photoemission spectroscopy (UPS). Two peaks in the band gap region of SrTiO3 (in-gap peaks) are induced by La substitution for Sr; a peak with a sharp Fermi cut-off (metallic peak) and a broad peak centered at ∼1.5 eV below EF(∼1.5 eV peak). The spectral intensity of the metallic peak and the ∼1.5 eV peak increases with the carrier concentration, but the spectral width of the metallic peak does not depend upon it. The behaviors of doping electrons on the electronic structure near EF of LaxSr1−xTiO3, such as no change in the spectral width of the metallic peak and the appearance of the ∼1.5 eV peak, can not be simply explained by the band theory.

We present detailed energy dispersions near the Fermi level along the high symmetry line GammaX on the monolayer and bilayer strontium ruthenates Sr2RuO4 and Sr3Ru2O7, determined by high-resolution angle-resolved photoemission spectroscopy. A kink in the dispersion is clearly shown for the both ruthenates. The energy position of the kink and the slope in the low-energy part near the Fermi level are almost identical between them, whereas the dispersion in the high-energy part varies, like the behavior of the kink for the cuprate superconductors.

By using ultra-violet photoemission spectroscopy (UPS) and soft x-ray absorption spectroscopy (XAS), we have observed a systematic change of the spectral function around the Fermi level in the perovskite-type conductive 3 d 1 system, Ca 1−x Sr x VO 3 . When we decrease the Sr concentration (x) from 1 to 0 in Ca 1−x Sr x VO 3 , UPS and XAS intensities near the Fermi level decrease, and the reduced spectral weight is transferred to high energy part about 2 eV below and above Fermi level. The high energy features are thought to correspond to the remnants of lower and upper Hubbard bands, and the spectral weight within ∼1eV of Fermi level is assigned to the quasiparticle excitations or renormalized 3 d -band. That is, the observed systematic spectral change indicates the opening of Mott-Hubbard gap.

The electronic structure of reduced SrTiO3(110) surface prepared by annealing in ultrahigh vacuum (UHV), has been studied using photoemission spectroscopy (PES) and scanning tunneling microscopy/spectroscopy (STM/STS). In the PES spectra of reduced SrTiO3(110) surface after annealing in UHV at 800°C, a clear metallic state with a sharp Fermi cut-off and a broad state centered at ∼1.1eV below the Fermi level are observed in the band gap region. A Ti3p->3d resonance enhancement is occurred for the metallic state, but not for the ∼1.1eV state. On the other hand, after the sample was annealed in UHV at 1000°C, it has been shown that the metallic state becomes drastically weak, and that only the ∼1.1eV state is seen in the band gap region. Thereafter, the ∼1.1eV state exhibits a clear Ti3p->3d resonance enhancement. The difference in the spectral feature of these band gap states is directly related to the surface geometric structural change.

The electronic structure of La 2−x Ba x CuO 4 (x∼0.125) has beenstudied by ultraviolet photoemission spectroscopy. It is found that the LTO->LTT phase transition has little effect on the electronic density of states (DOS) near the Fermi level. This suggests that the DOS change is not the main cause of the suppression of superconductivity, contrary to previous reports. We also make a comparison between La 2−x Ba x CuO 4 (x≈0.125) and La 2−x Sr x CuO 4 (x≈0.15) in the electronic DOS.

We have studied effects of surface oxygen vacancies on electronic states of TiO 2 (110), TiO 2 (001) and SrTiO 3 (001) surfaces by means of angle-resolved photoemission spectroscopy. The surface oxygen vacancy induces a state at ∼1 eV below the Fermi level in the bulk band gap. In the angle-resolved photoemission spectra, this state has slight energy dispersion and doesn't cross the Fermi level when the emission angle is changed. These results indicate that the state induced by surface oxygen vacancies is not simply interpreted by delocalized model, and that the localized behavior also plays an important role for the metal-insulator transition of these materials.

Microscopic structure and electronic states on the BaTiO3(100) single-crystal surfaces annealed in ultrahigh vacuum were observed by scanning tunneling microscopy and spectroscopy (STM/S). The surface step edges aligned preferentially along the [001] family of axes as the annealing temperature was increased. After annealing at temperatures above 800° C, spatial ordering of Ti 3d-oxygen vacancy complexes appeared on the surface. The STS spectra showed in-gap electronic states at about 1.0 eV below Fermi energy, which agreed well with the results of ultraviolet photoelectron spectroscopy previously reported.

Structure and electronic states on the (100) surface of reduced BaTiO3 single crystals were observed by scanning tunneling microscopy and spectroscopy. After annealing at 1150 °C, the direction of the edges ordered to run along the equivalents of [011] and [001] directions. All the observed step edges were of unit‐cell height. On each terrace atomlike corrugation with the periodicity multiples of the √5×√5 R26.6° superlattice was observed in the filled state images. A straightforward method to deduce the local density of states from the scanning tunneling spectroscopy data was introduced, based on multiplication of an inverted triangular transfer matrix, and was applied to the scanning tunneling spectroscopy data on the terraces. The amplitude of the local density of states at EF−1 eV varied in phase with the atomlike corrugation on the terrace, which was consequently ascribed to electronic states at the spatially ordered Ti 3d–oxygen vacancy complexes on the surface.

We have performed angle-resolved photoemission and X-ray photoemission studies for Stoichiometric and reduced SrTiO3(100) surfaces. In the empirical band structure of the O2p valence bands along the whole Δ line in the bulk Brillouin zone, there is no essential difference between the Stoichiometric and reduced surfaces. Our results are in excellent agreement with the calculation. In addition to the O2p valence band structure, two new states at ∼1 eV and ∼11 eV below Fermi level appear for the reduced surface (but not for the stoichiometric surface). We show that both of these states are closely connected with oxygen vacancies near the surface.

The electronic state of oxygen adsorbed on a Cr(110) surface at 80 K has been studied by angle-resolved photoemission spectroscopy with synchrotron radiation. Dissociative chemisorption occurs up to \ensuremath{\sim}2 L, and then oxidation starts at \ensuremath{\sim}4 L, leading to the formation of a disordered ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$ layer. An emission at \ensuremath{\sim}7.5 eV below the Fermi energy, being attributable to a chemisorbed ${\mathrm{O}}_{2}$ molecule, was observed at above \ensuremath{\sim}20 L. Dispersion effects on the ${\mathrm{O}}_{2}$p--derived levels were found for the Cr(110)p(4\ifmmode\times\else\texttimes\fi{}2)-O and faceted Cr(110)-O surfaces produced by annealing.

The electronic energy-band properties of epitaxially grown YBa/sub 2/CuO/sub 3/O/sub 7-//sub x/(001) single-crystal thin films have been investigated by angle-resolved ultraviolet photoemission spectroscopy (ARUPS) with synchrotron radiation as the light source. The (001) surfaces exhibit sharp (1 x 1) low-energy electron-diffraction patterns. Our ARUPS data show a clear Fermi edge and dispersive nature of the valence bands, suggesting the validity of the band concept for this oxide. We determined energy-band dispersion along the GAMMA-X-M-GAMMA directions in the bulk Brillouin zone. The experimental results are compared with the existing ground-state band calculations.

Piezoreflectance spectra of potassium iodide were measured from 5 to 30 eV in the fundamental and core excitation region. The deformation potentials cubic, tetragonal and trigonal, were deduced for twenty six structures observed in this energy region and are analyzed in terms of a simple point ion model to identify the electronic origins of these structures.

Angle-resolved photoemission from epitaxially grown $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}(001)$ single-crystal thin films reveals a clear Fermi edge and fine structure near the edge. Some of the valence-band photoemission features show $k$-space dispersion. These new results suggest that the electronic structure of this oxide can be treated within the framework of the one-electron band picture.

The reflectivity spectrum of Y 3 Al 5 O 12 (YAG) single crystals at 297 K is presented in the region of 6.734 eV ≤ E ≤116 eV. The spectra of optical constants derived from the reflectivity by the Kramers-Kronig analysis are tentatively interpreted in terms of the energy levels of the constituent atoms of YAG. Plasma resonance peaks are found at 23.3 8 eV and 36.2 0 eV in which the valence-band electrons and valence- as well as full-band electrons participate, respectively. The structure of absorption due to excitations of the electrons in the Al 3+ L 2,3 levels is found in the region of E ≥76 eV. The free electron-like absorption calculated by the Drude formula by use of the line shape parameters of the plasma resonance line is compared with the dielectric constant in the region of E ≥24 eV. The effective optical dielectric constant calculated from the optical constant e 2 is found to be in good agreement at 116 eV with the optical dielectric constant derived from the dispersion formula.

The electronic state of the hydrogen-adsorbed Cr(110) surface at 80 K has been investigated using angle-resolved photoemission spectroscopy. We observed a p(2\ifmmode\times\else\texttimes\fi{}2) low-energy electron-diffraction pattern at \ensuremath{\sim}2 L, and a ``streaked'' (1\ifmmode\times\else\texttimes\fi{}1) pattern along the [11\ifmmode\bar\else\textasciimacron\fi{}0] azimuth at above 10 L. The photoemission results show that for the p(2\ifmmode\times\else\texttimes\fi{}2) phase an H 1s--derived state, having a nearly constant binding energy of \ensuremath{\sim}5.5 eV below the Fermi level, is observed in the outer part of the surface Brillouin zone, that is, outside the Cr s-p band projections. [Here 1 langmuir (L)\ensuremath{\equiv}${10}^{\mathrm{\ensuremath{-}}6}$ Torr sec.] On the other hand, for the streaked (1\ifmmode\times\else\texttimes\fi{}1) phase, an H 1s--derived state, split off from the Cr bulk bands, is found at the binding energy of 7.8 eV at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} and shows considerable dispersion of \ensuremath{\sim}2.8 eV in the [001] azimuth being consistent with the periodicity of the substrate structure. In addition, a H-induced surface state is found at 2.5 eV at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} for both phases. The nature of the Cr-H chemisorption bond is discussed.

Two-dimensional band dispersion was studied by angle-resolved photoemission for a p(2\ifmmode\times\else\texttimes\fi{}2)-Xe overlayer on Cr(110) with a Xe-Xe nearest-neighbor distance of 4.99 A\r{}, which is much larger than earlier reported values. The Xe 5${p}_{1/2}$ and 5${p}_{3/2}$ levels show \ensuremath{\sim}0.2 eV dispersion in good agreement with known theoretical results for the isolated layer, which confirms the theoretical prediction that the bandwidth is exponentially dependent on the interatomic spacing within the layer.

Carbon-contaminated mirrors and gratings have been cleaned by a d.c. glow discharge in oxygen. The reflectance of mirrors and the efficiency of gratings were measured in situ before and after cleaning in the photon-energy range 4 ~ 40 eV or 100 ~ 1000 eV using reflectrometers which incorporated a discharge electrode. Angle-resolved scattering of mirrors and diffraction patterns of gratings were also measured. The mirror reflectance was restored to that of original mirror materials and the scattering level was reduced rather than increased by the discharge cleaning. The grating efficiency of the inside first order was drastically improved by cleaning, even by nearly an order of magnitude in some energy regions. Furthermore, the effect of a blaze was shown to be recovered by examining changes in the efficiencies of other orders as well.

In addition to our previous results [Phys. Rev. B 38, 1131 (1988)], we report further photoemission evidence for the bulk magnetic phase transition in Cr. An emission from the ${\ensuremath{\Sigma}}_{4}$ and ${\ensuremath{\Sigma}}_{1}$ bands unique to the paramagnetic phase disappears at above the N\'eel temperature.