W. P. Ellis

Electronic structure of the quenched superconductivity materials Y1−xPrxBa2Cu3O7−δ☆

Abstract The superconductivity of the Y 1− x Pr x Ba 2 Cu 3 O 7−δ system is quenched as x increases. It has been speculated that praseodymium has a valence of 4+, which results in extra charge in the Cu-O planes, and causes quenching of T c . To study the electronic state of praseodymium, the valence band resonant photoemission of the Y 1− x Pr x Ba 2 Cu 3 O 7−δ system was measured for x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0. It was found that the praseodymium valence is close to 3+ for all x values and that the extracted Pr 4f spectral weight has a complex line shape. This line shape implies extensive Pr 4f-O 2p/Cu 3d hybridization which probably causes the quenching of T c by disrupting the electronic or magnetic structure of the x = 0 material, perhaps via Pr-Cu and Pr-O superexchange interactions.

Fermi surfaces and single-particle spectral functions of low-dimensional inorganic non-cuprate compounds: the molybdenum bronzes

The Fermi surfaces and single-particle spectral functions of several low-dimensional materials have been measured as part of an effort to assess the occurrence of non-Fermi-liquid behaviour in non-cuprate materials.

The band structure of UO2: An angle resolved and resonant photoemission study☆

Abstract A detailed study of angle resolved photoemission of UO2 〈100〉 in the normal emission configuration is presented. The results are compared with a semirelativistic linearized augmented plane wave (LAPW) band calculation with the actual calculated empty bands used in the data reduction. Excellent agreement is found with calculations both for filled states as well as critical points in the empty states with no adjustment of bands, f-p Hybridization is found at the leading edge of the valence band and not at the bottom of the valence band, p-d Hybridization is found throughout the valence bands.

Angle-resolved photoemission of quasi-one-dimensional metals: Evidence for luttinger liquid behavior

Abstract We present angular resolved photoemission data of the quasi-one-dimensional metals K 0.3 MoO 3 and (TaSe 4 ) 2 I. The measured conduction band dispersions reflect the highly anisotropic nature of these materials. However, no clear Fermi-Dirac cutoff is observed in the spectra above the Peierls transition, being due to either charge density wave (CDW) fluctuations or due to electronic correlation effects in one dimension. The experimental conduction band width of (TaSe 4 ) 2 I agrees well with a tight-binding calculation, suggesting a description as a conventional Peierls system with CDW fluctuations suppressing the spectral weight at the Fermi energy. In contrast, the spectra of K 0.3 MoO 3 show an excitation which along the direction of highest conductivity (“easy axis”) disperses 5 times faster than expected from band theory. This anomalous increase cannot be explained by electron-electron or electron-phonon interactions in a Fermi liquid scenario, but can be accounted for as holon dispersion in a Luttinger liquid framework, which need not conflict with the materials CDW properties.

Valance-Band photoemission intensities in thorium dioxide

Abstract Resonant photoemission spectra of the O 2p-derived valence band of insulating ThO2 are compared to linear muffin-tin orbital (LMTO) density-of-state (DOS) and XPS intensity calculations. At Th 5d corelevel threshold energies (85 ⩽ hv ⩽ 120 eV), resonance is greatest at the bottom of the O 2p band where calculated p/d hybrid states are greatest; p/f hybrid content is weak by comparison. We conclude that the dominant hybridization is between O 2p states and Th 6d.

Electron spectroscopy study of the heavy Fermion compound URu2Si2

Abstract We report x-ray photoemission, resonant photoemission and bremsstrahlung isochromat spectra of the 4f core levels, the valence band and the conduction band, respectively, of the heavy fermion compound URu 2 Si 2 . The resonant photoemission behavior of the uranium 5f weight resembles that of cerium 4f weight in that the portion away from the Fermi energy has a delayed resonance relative to that at the Fermi energy. We also assess current efforts to interpret uranium spectra.

Kondo resonance behavior of heavy fermion f-electron materials (invited)

The Kondo properties of the impurity Anderson model provide a theoretical framework for relating thermodynamic and angle integrated electron spectroscopy data in many heavy fermion materials. We describe the success and the challenges of this approach, summarize a detailed analysis of CeSi2, and give a perspective on the relation to the lattice Anderson model.

CORE-LEVEL AND VALENCE-BAND X-RAY PHOTOELECTRON DIFFRACTION IN UO2 (100)

Abstract X-ray photoelectron diffraction (XPD) effects have been studied in the U 4f, 0 1s and valence-band spectra of UO 2 (100). A simple nearest-neighbor forward-scattering model adequately explains the intensity modulations which occur with changes in polar angle, θ. In the valence band, the U 5f and U 6p 3 2 peaks and the 0 2p band show very similar angular intensity variations showing that the 0 2p bands intensity is largely U-orbital derived.

Valence-band densities of state in NiAs

Abstract Valence-band resonant photoemission data on NiAs are compared to corrected linear muffin-tin orbital (LMTO) density-of-state (DOS) calculations. The observed bandwidth is 6 eV with the main Ni 3d peak at 1.8 ev below the Fermi edge and shoulder ∼1 eV wide at E F , in agreement with the calculated Ni d-projected DOS.

Electron Spectroscopy and Hubbard: Issues and Opportunities

A fundamental theoretical characterization of a many-body system such as that defined by the Hubbard Hamiltonian is the single particle Green’s function G. Single particle electron spectroscopies provide a means to measure the spectral weight of G and so these spectroscopies are in principle a very powerful experimental means of testing theoretical predictions for the Hubbard model. This article gives an overview of problems and opportunities associated with the application of electron spectroscopy to this problem.