D.D. Koelling

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.

Photoemission study of 5f localization in UPd3−x(Pt,Rh)x

Photoemission measurements in the two systems UPd3−x(Pt,Rh)x show that the 5f spectra are consistent with localized 5f electrons (peak in spectral weight is below EF for all x within the double hexagonal DO24 phase) while at both phase transitions the 5f peaks lock in at EF consistent with intinerancy. A satellite 5f peak which we attribute to d screening is observed in both localized and itinerant systems.

The electronic structure and properties of the C15 compounds CeAl2, LaAl2 and YAl2

Abstract Results of self-consistent band calculations are reported for the C15 structured XAl 2 materials (X = Y, La, and Ce) using the local spin density functional formalism for assumed ferromagnetic and antiferromagnetic states as well as the paramagnetic state. The X-atoms are found to be the dominant factor is determining the electronic structure near the Fermi energy and this is enhanced by the presence of f-bands close to (LaAl 2 ) or at (CeAl 2 ) the Fermi energy. In paramagnetic CeAl 2 , the f-bands are about 1 eV wide and, although principally above the Fermi energy, extend down to accomodate the additional electron compared to LaAl 2 . The ferromagnetic state is found not to be stable. By contrast, the antiferromagnetic state is found to be stable with a magnetic moment of 0.88μ B per Ce atom in very good agreement with the maximum moment, 0.89μ B found in the neutron measurements of Barbara et al. A significant narrowing of the f-bandwidth is observed in the antiferromagnetic state. The antiferromagnetic spin density ordering appears to be related to nesting features in this underlying Fermi surface in LaAl 2 (i.e., no 4f electron) rather than that of CeAl 2 .

Oscillation period of the interlayer coupling for epitaxial Fe/Cr1−xVx(100) and (211) superlattices

The microscopic origin of the 18 A period in the oscillatory interlayer exchange coupling of Fe/Cr(100) and (211) superlattices is investigated by alloying the Cr spacer with V to alter its Fermi surface. The addition of V increases or decreases in size the various Fermi surface calipers that are candidates for governing the oscillation period, such as those that span the ellipse, lens, octahedron, and nested sheets. Epitaxial sputtered superlattices of (100) and (211) orientation were grown and characterized via magnetoresistance measurements as a function of spacer layer thickness for different V-doping levels. A small decrease of the oscillation period is found experimentally which strongly implicates the N-centered ellipse as the origin of the 18 A period in Fe/Cr superlattices.

Self-consistent spin polarized energy band structure and magnetism in ZrZn2 and TiBe2

Abstract Results of self-consistent spin-polarized semirelativistic linear muffin-tin orbital energy band studies of TiBe 2 and ZrZn 2 are reported. The calculated magnetic moments, spin magnetization densities and neutron magnetic form factors - and their comparison with experiment - are used to discuss itinerant ferromagnetism in ZrZn 2 and TiBe 1.8 Cu 0.2 .

Photoemission study of 5f localization in UPd/sub 3-//sub x/(Pt,Rh)/sub x/

Photoemission measurements in the two systems UPd3−x(Pt,Rh)x show that the 5f spectra are consistent with localized 5f electrons (peak in spectral weight is below EF for all x within the double hexagonal DO24 phase) while at both phase transitions the 5f peaks lock in at EF consistent with intinerancy. A satellite 5f peak which we attribute to d screening is observed in both localized and itinerant systems.

Electron spectroscopy in narrow band f-electron compounds☆

Abstract We show by the combined means of high-resolution photoemission measurements at low temperatures on uranium and cerium compounds (including heavy fermions) and systematic resonant data on a series of uranium narrow-band compounds, that the “two-peaked” f-electron spectrum commonly found in cerium compounds is also found in uranium compounds. The 5f spectra consist of a superposition of features consistent with the band structure ground state plus a 5f satellite due to poorly-screened final state effects.

Electronic structure of LaN: Prediction of a small band overlap semi-metal☆

Abstract Results of a detailed theoretical investigation are reported which appear to resolve whether LaN is a semiconductor or a semi-metal. It is found that LaN has a band overlap of approximately 40 mRy making it a semimetal. A detailed analysis of the physical approximations and of the numerical precision indicate that this result has an uncertainty of ∼ 15 mRy which is too small to alter the conclusion.

Electronic structure, charge transfer excitations and high temperature superconductivity

High precision local density electronic band structure results (for YBa2Cu3O7, YBa2Cu3O6 and GdBa2Cu3O7) lead to the possibly important role of charge transfer excitations as the mechanism of high-Tc superconductivity, and explain the coexistence of magnetism and superconductivity in the high-Tc rare-earth superconductors.

Band structure aspects of materials with localizing f-orbitals

Abstract In those materials where the f-states are hybridized, a band structure provides a reasonable description of the ground state. This is amply demonstrated by the successful determination of the Fermi surfaces of CeSn 3 , URh 3 , UIr 3 and UGe 3 . But when the f-states become more local, inadequacies of the functionals employed yield incomplete localization. Thus, to obtain a good description of the Fermi surface for high field ferromagnetic CeSb, the local character of the f-orbitals is artificially forced to produce the standard rare earth model. When dealing with excited states, the ground state band structure provides only part of the story. Even thermal excitations can provide significant departures from the ground state as evidenced by the large enhancements found for some materials. The series USi 3 , UGe 3 and USn 3 (together with CeSn 3 ) demonstrate the effect very well. NpSn 3 provides a useful counter example demonstrating that such enhancements need not be a universal property of localization. In photoemission, the excited state can exhibit a more local character than the ground state as is clearly seen in the analysis of the Ce pnictides. But to emphasize this, it is useful to compare Ce and U compounds where it can be asserted in one limited definition that Ce acts more itinerant than U in the ground state. Yet it is Ce which shows the correlation derived second f-peak. The URh 3 B x interstitial alloy system provides a concrete example of the situation in the uranium compounds.