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Understanding characteristic energy scales is a fundamentally important issue in the study of strongly correlated systems. In multiband systems, an energy scale is affected not only by the effective Coulomb interaction but also by the Hund's coupling. Direct observation of such energy scale has been elusive so far in spite of extensive studies. Here, we report the observation of a kink structure in the low energy dispersion of NiS2−xSex and its characteristic evolution with x, by using angle resolved photoemission spectroscopy. Dynamical mean field theory calculation combined with density functional theory confirms that this kink originates from Hund's coupling. We find that the abrupt deviation from the Fermi liquid behavior in the electron self-energy results in the kink feature at low energy scale and that the kink is directly related to the coherence-incoherence crossover temperature scale. Our results mark the direct observation of the evolution of the characteristic temperature scale via kink features in the spectral function, which is the hallmark of Hund's physics in the multiorbital system. A decisive spectroscopic evidence of the Hund's coupling energy scale in multi-orbital correlated systems has been lacking. Here, the authors identify a kink feature due to Hund´s coupling in the spectral function of NiS2xSex as they track its evolution across the Mott-insulator transition. [ABSTRACT FROM AUTHOR]

The epitaxial growth of Cu on Ag(111) was explored on monitoring the evolution of its surface states with angle-resolved photoemission spectroscopy; the chemical element on the top of Cu islands on Ag(111) with a (9×9) reconstruction was determined to be not Cu but Ag. Our result demonstrates a technique with which the chemical property associated with a surface state is explorable and an identification of the chemical element in the topmost layer of the surface becomes feasible. [ABSTRACT FROM AUTHOR]

Abstract: From an examination of the Al(100) surface band structure with high-resolution angle-resolved photoelectron spectra, we identified three surface states. Features in the surface band structure predicted theoretically were confirmed experimentally, including the dispersion of the surface state within the narrow band gap centered at , an avoided crossing between two surface states along , and the dispersion of the surface state within the symmetry gap along . The electron–phonon coupling strength of the surface state at was determined. Our results indicate that there is no thermally induced defect on Al(100) from 90 to 420K. Our photoemission data serve as reference for future investigation and motivate re-examination of many systems with contemporary photoemission instruments. [Copyright &y& Elsevier]

An exfoliated Kish graphite sample on a heavily n -doped Si substrate covered with native oxide was prepared with a conventional micromechanical cleavage method. From angle-resolved photoemission spectra (ARPES), we measured the band structure of graphite over photon energies from 28 eV to 116 eV. The inner potential V 0 = 17.25 eV is determined with a period from the band dispersion in the KH direction. A set of parameters in the tight-binding method and the SWMcC model for graphite is extracted from the fitted results. A comparison of constant-energy mapping results at large binding energy indicates the reliability of the tight-binding parameters extracted from the ARPES results. [ABSTRACT FROM AUTHOR]

The growth of Cu on Ag(1 1 1) under varied growth conditions was investigated with angle-resolved photoemission spectra. The evolution of Cu/Ag(1 1 1) during annealing was characterized on monitoring its surface states. The surface morphology of a Cu film on Ag(1 1 1) depends on the temperature and the Cu coverage. Islands or crystalline films develop when Cu is deposited at ∼300 K. Defects in the Cu films penetrate deeply into the Ag(1 1 1) substrate and expose the Ag(1 1 1) surface. The deposition of Cu at a low temperature results in disordered films. On annealing, the films become ordered with defects. Our results show the segregation of Ag on the Cu surface, which occurs at 300 K and becomes accelerated significantly at ∼380 K. After being annealed above 430 K, all islands and films of Cu are fully covered with Ag, showing a (9 × 9) reconstruction. Our results indicate also that the segregation of Ag on the Cu surface occurs only after the Ag(1 1 1) surface is exposed, indicating that Ag atoms migrate to the Cu(1 1 1) surface, not through bulk Cu, but along the walls of the islands and the defects in the films. [ABSTRACT FROM AUTHOR]

To investigate the surface diffusion of chemisorbed H on Ag/Au(lll) thin films with surface steps, we characterized the distribution of H atoms on the surface by measuring the Shockley states of these surfaces with angle-resolved photoelectron spectroscopy. Our results show that H atoms tend to diffuse and to remain on the terrace at the lower side of the surface steps during annealing. This diffusive behavior is explained qualitatively through the existence of an Ehrlich-Schwoebel potential barrier associated with the surface steps. [ABSTRACT FROM AUTHOR]

We performed an x-ray spectroscopic study combining resonant x-ray emission spectroscopy (RXES) and photoelectron spectroscopy on the superconducting ternary silicide YbGa1.15Si0.85 and nonsuperconducting ternary germanide YbGaxGe2-x (x = 1.0 and 1.1). The Yb valence for all three compounds is found to be about 2.3. In YbGa1.15Si0.85 no temperature dependence of the Yb valence is observed in the RXES spectra in the temperature range of 7–300 K, while the valence shows a drastic increase under pressure from the Yb2+ state partially including itinerant electrons to the localized Yb3+ state. Differences are observed in the valence-band spectra of the photoelectron spectroscopy between YbGa1.15Si0.85 and YbGaxGe2-x, which may be attributed to the difference of crystal structure. We conclude that both the crystal structure of the planar GaSi layer in YbGa1.15Si0.85 and the resultant electronic structure may have a crucial role in the occurrence of superconductivity. [ABSTRACT FROM AUTHOR]