Temperature-dependent High-resolution Photoemission Research Articles

Ultrahigh-Resolution Photoemission Spectroscopy on UGe2

We have performed temperature-dependent high-resolution photoemission spectroscopy on UGe 2 . The spectrum shows a sharp peak with a dominant U 5 f character near the Fermi level ( E F ), in good agreement with the band structure calculation based on the itinerant U 5 f model. The peak gradually moves toward E F with increasing temperature across the Curie temperature ( T C ), indicating the temperature-induced change of the density of states near E F . The present results are well interpreted in terms of the Stoner-like temperature-dependent density of states responsible for the occurrence of the ferromagnetism below T C .

Temperature-dependent metal-insulator transition in d- and f-electron systems studied by high-resolution photoemission spectroscopy

Abstract We have studied metal-insulator transition (MIT) of Y 1− x Ca x TiO 3 ( x =0.37, 0.39 and 0.41) single crystals and a Kondo semiconductor Ce 3 Bi 4 Pt 3 single crystal by temperature-dependent high-resolution photoemission spectroscopy. At the phase boundary between insulating and metallic states of Y 1− x Ca x TiO 3 ( x ∼0.4), an unusual temperature-dependent spectral-weight redistribution has been observed. The x =0.39 compound showed a clear MIT at ∼150 K: a finite spectral weight at E F appears below ∼150 K. A narrow V-shaped pseudogap is formed in the conduction band of Ce 3 Bi 4 Pt 3 below a characteristic temperature T coh ∼100 K. The spectral weight of the Ce 4f state at E F increases above T coh on cooling, but reduces significantly below T coh forming a V-shaped pseudogap. It is a clear evidence for the crossover from an incoherent state above T coh to a coherent state below T coh . In these materials, electron correlation and intersite-hybridization interactions (or a bandwidth) are both important for the temperature-dependent MIT.

High-resolution temperature-dependent photoemission study of metal–insulator transition of Y 1− xCa xTiO 3

Temperature-dependent high-resolution photoemission spectroscopy has been performed on Y 1− x Ca x TiO 3 ( x=0.37, 0.39, and 0.41) single crystals. Ti 3d photoemission spectra have an incoherent part, indicating electrons in the Ti 3d bands are strongly correlated. Although the temperature dependence of the incoherent part at 150 K for the present samples is continuous and nearly the same, the spectral intensity near E F of the x=0.39 composition clearly shows the metal–insulator transition at ∼150 K, indicating the importance of the carrier density in the Ti 3d bands.

Temperature-dependent high-resolution photoemission study of the Kondo insulator Ce3Bi4Pt3

Abstract Temperature-dependent high-resolution photoemission spectroscopy was performed on the Kondo insulator Ce3Bi4Pt3. The spectral weight near the Fermi level (EF) is reduced as temperature decreases, especially below ∼100 K. The temperature-dependence of the Ce 4f states was obtained by taking the difference between the He II and He I spectra. The Ce 4f spectrum near EF at 6 K shows a clear dip structure, indicating the opening of a (pseudo)gap at low temperature.

Temperature-Dependent High-Resolution Photoemission Study of Y1-xCaxTiO3

Temperature-dependent high-resolution photoemission spectroscopy has been performed on Y1-xCaxTiO3 (x=0.37, 0.39, 0.41) single crystals. Electrons in Ti 3d bands are strongly correlated and clear metal-insulator transition is observed in the photoemission spectra for x=0.39. The spectral shapes of O 2p and Ti 2p states are temperature dependent indicating strong coupling between electronic states and lattice distortion.

Single-particle gap above the Verwey transition inFe3O4

The Verwey transition in magnetite, ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$, has been studied using temperature-dependent high-resolution photoemission spectroscopy. On heating through the transition temperature ${\mathrm{T}}_{\mathrm{V}}$ the band gap is not collapsed, but is merely reduced by \ensuremath{\sim}50 meV, showing that a metal-insulator transition does not occur. The change in the gap is perfectly consistent with the two orders of magnitude conductivity jump at ${\mathrm{T}}_{\mathrm{V}}$. Thus even above ${\mathrm{T}}_{\mathrm{V}}$ short-range charge ordering rather than site equivalency dominates the single-particle excitations and the electrical properties. We also point out important implications for efforts to model the electrical transport above ${\mathrm{T}}_{\mathrm{V}}$.