[en] We report high-resolution angle resolved photoemission studies of 2H-NbSe₂ and 2H-TaS₂. Results are compared to those of 2H-TaSe₂. We find that the normal state electronic structures in this family of materials have the same basic characteristics. Their Fermi surface consists of a pocket around Γ and another one around K. They all exhibit a saddle band near E_F along Γ-K. A finite energy gap is observed in the saddle band region and on the Fermi surface around K in 2H-TaS₂ and 2H-TaSe₂. Gapping on the Fermi surface around Γ was not observed. We suggest that the charge density waves in this family of materials originate from a combination of the partial nesting of the Fermi surface around K and the saddle band

[en] X-ray and soft x-ray photoelectron spectra were taken on Fe₂VAl samples. The Fe-3s spectra show a shoulder on the higher binding energy side of the main peak, split by ∼4.7 eV. Based on current understanding of core-level multiplet splitting in transition-metal compounds, we believe this is direct evidence of a local moment in Fe₂VAl

[en] We report a detailed study of the electronic structure of Bi₂Te₃, to our knowledge the best room temperature thermoelectric material known to date, using angle-resolved photoemission. Dispersions of the valence bands were determined. A sixfold k-space degeneracy in the valence-band maximum is found. The quasi-two-dimensional nature of the electronic structure was demonstrated by the weakly dispersive bands along the Γ-Z direction. Experimental results are compared with theoretical band-structure calculations and with de Haas--van Alphen and Shubnikov--de Haas experiments

[en] Satellites on the low-binding-energy side of core-level photoelectron emission due to extra 4f screening are a well-known feature in the x-ray photoelectron spectra of valence fluctuation materials and rare-earth metals. A notable exception is Eu metal, where up to now no low-binding-energy satellite has been observed. In this paper we show that in Eu metal the 4d-4f resonance can decay via a resonant Auger decay, which is not a constant kinetic-energy feature due to a rapid change of the strength of 4f screening with excitation energy, establishing a low-binding-energy replica of the 5p core-level photoelectron emission. (c) 1999 The American Physical Society

[en] We have demonstrated that oxidation states in uranium-oxides such as UO₂ and U₃O₈ can be controlled through epitaxial stabilization by growing single-crystal-like films. We have further shown that the growth of polymorphic uranium oxides is feasible by using different substrates with appropriate in-plane lattice parameters. The clearly improved stability of epitaxial uranium-oxides illustrates the significance of crystal lattice pinning on the control of surface chemistry of materials. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

[en] The Fermi surface (FS) of 2H-TaSe₂ was investigated by high resolution angle resolved photoemission. Two FS pockets, one centered at the Γ point and the other centered at the K point, were observed and are found to be in excellent agreement with the band calculation results. Although the FS centered at the Γ point appears to have nested segments with the observed charge density wave (CDW) wave vectors, the CDW-induced energy gap is nearly zero on that FS. Instead, the gap opens in the extended saddle band region and on the FS centered at the K point. The implication of these results on the CDW mechanism is discussed. (c) 2000 The American Physical Society

[en] Little is known about the impact of the electron-photon matrix element on angle-resolved photoelectron spectra of layered cuprate compounds. Using the example of the model layered cuprate Sr₂CuO₂Cl₂, we demonstrate that the electron-photon matrix element has a significant influence on energy distribution curves, rendering their interpretation as images of the spectral function nontrivial. (c) 2000 The American Physical Society

[en] We report angle resolved photoemission studies of La_0.66Ca_0.33MnO₃ and La_1.2Sr_1.8Mn₂O₇ using single crystal samples. The Mn 3p-3d resonance photoemission data of La_0.66Ca_0.33MnO₃ show that the states at 2.5 eV binding energy have predominantly Mn 3d character, qualitatively consistent with the predictions of local spin density approximation calculations except for a 1 eV shift toward higher binding energy. Band dispersions are observed in the normal emission data. The spectra of La_1.2Sr_1.8Mn₂O₇ show well defined features and strong matrix element effects, indicating excellent surface quality. (c) 2000 American Institute of Physics

[en] Electronic structures of UTSn (T = Ni, Pd) have been investigated using photoemission spectroscopy (PES). The extracted U 5f PES spectra of UTSn (T = Ni, Pd) exhibit a broad peak centred at ∼ 0.3 eV below E_F with rather small spectral weight near E_F (N_f(E_F)). The small N_f(E_F) in UTSn is found to be correlated with the T d PES spectra that have a very low density of states (DOS) near E_F. The temperature-dependent high-resolution PES spectra of UTSn provide evidence for the V-shaped reduced metallic DOS near E_F, but they reveal no appreciable changes in their electronic structures across the magnetic phase transition temperatures. Comparison of the measured PES spectra to the LSDA +U band structure calculation shows reasonably good agreement for UPdSn, but not for UNiSn. Therefore, in contrast to the general consensus of the localized U 5f electrons in UTSn (T = Ni, Pd), our finding supports a rather itinerant nature of U 5f electrons for UPdSn, but not for UNiSn

[en] The electronic structure of CeTe₂ has been investigated by performing high-resolution photoemission spectroscopy (PES) measurements on high-quality stoichiometric single crystals of CeTe₂. The Ce 3d XAS measurement indicates that the Ce ions are trivalent. The Ce 4f PES spectrum reveals two-peak structures with the Ce 4f bulk hybridization peak located around 0.8 eV below E_F. The high-resolution, high-energy, bulk-sensitive PES study of CeTe₂ provides evidence for a metallic density of states near E_F. The carriers near E_F consist mainly of Ce 5d and Te(1) 5p states, while the contribution from the Ce 4f and Te(2) 5p states is negligible. This finding agrees with the CDW instability in the Te(1) sheets