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Title: Observation of Dynamical spin shielding in Ce: Why It Matters for Pu Electronic Structure

Abstract

In a series of experiments and linked theoretical modeling, the range of possible solutions for Pu electronic structure has been dramatically reduced. Nevertheless, the key issue of electron correlation remains.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
908104
Report Number(s):
UCRL-CONF-229124
TRN: US0703620
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: 37th Journees des Actnides, Sesimbra, Portugal, Mar 24 - Mar 27, 2007
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ELECTRON CORRELATION; ELECTRONIC STRUCTURE; SHIELDING; SIMULATION; SPIN; CESIUM; PLUTONIUM

Citation Formats

Tobin, J G, Yu, S W, Chung, B W, Morton, S A, Komesua, T, and Waddill, G D. Observation of Dynamical spin shielding in Ce: Why It Matters for Pu Electronic Structure. United States: N. p., 2007. Web.
Tobin, J G, Yu, S W, Chung, B W, Morton, S A, Komesua, T, & Waddill, G D. Observation of Dynamical spin shielding in Ce: Why It Matters for Pu Electronic Structure. United States.
Tobin, J G, Yu, S W, Chung, B W, Morton, S A, Komesua, T, and Waddill, G D. Thu . "Observation of Dynamical spin shielding in Ce: Why It Matters for Pu Electronic Structure". United States. doi:. https://www.osti.gov/servlets/purl/908104.
@article{osti_908104,
title = {Observation of Dynamical spin shielding in Ce: Why It Matters for Pu Electronic Structure},
author = {Tobin, J G and Yu, S W and Chung, B W and Morton, S A and Komesua, T and Waddill, G D},
abstractNote = {In a series of experiments and linked theoretical modeling, the range of possible solutions for Pu electronic structure has been dramatically reduced. Nevertheless, the key issue of electron correlation remains.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Mar 08 00:00:00 EST 2007},
month = {Thu Mar 08 00:00:00 EST 2007}
}

Conference:
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  • The valence electronic structure and electron spectra of Cerium remain a subject of uncertainty and controversy. Perhaps the best and most direct method of ascertaining the valence electronic structure is the application of electron spectroscopies [1-17], e.g. photoelectron spectroscopy for the occupied states [1-10, 12-14] and x-ray absorption [2] and Bremstrahlung Isochromat Spectroscopy (inverse photoelectron spectroscopy) [3,11,13] for the unoccupied states. Much of the controversy revolves around the interpretation of the Ce photoemission structure in terms of a modified Anderson Impurity Model [15,16]. Here, in this correlated and multi-electronic picture, semi-isolated 4f states (at a nominal binding energy of 1more » eV) are in contact with the bath of spd valence electrons, generating spectral features at the Fermi Level and at a binding energy corresponding to the depth of the bath electron well, about 2 eV below the Fermi Level in the case of Ce. This controversy has spilled over into issues such as the volume collapse associated with the alpha to gamma phase transition [17-19] and the electronic structure of Ce compounds [20-23]. (A more generalized schematic illustrating the competition between the bandwidth (W) and correlation strength (U) is shown in Figure 1.) Considering the remaining uncertainty associated with the spectral features and valence electronic structure of Ce, it seemed plausible that the situation would benefit from the application of a spectroscopy with increased resolution and probing power. To this end, we have applied circularly polarized soft x-rays and true spin detection, in a modified form of the photoelectron spectroscopy experiment, to the enigmatic Ce system. The result of this is that we have observed the first evidence of the Fano Effect in the valence electronic features of non-magnetic Cerium ultra-thin films.« less
  • The first fully relativistic calculations that also include spinpolarization are presented for the single-site t-italic matrix for Ce and Pu. The pattern of resonant energies for Ce are compared to recent atomic eigenvalue results for the Ce/sup 3+/ ion. The Ce band states are also determined along the <100> and <111> directions in the Brillouin zone by solving the Dirac equation with an internal magnetic field constructed from scalar relativistic linear muffin-tin orbital (LMTO) spin-polarized calculations. In the relativistic case the coupling between spin-orbit and spin-polarization interactions destroys rotational symmetry, unlike in the nonrelativistic spin-polarized formalism, and hence leads tomore » completely nondegenerate f-italic and d-italic states in these systems (similar to the Zeeman effect). To see this we also give results for an applied magnetic field that only couples to the spins and hence resembles an effective internal spin-polarized field.« less
  • Using Fano Effect measurements upon polycrystalline Ce, we have observed a phase reversal between the spectral structure at the Fermi Edge and the other 4f derived feature near a binding energy of 2 eV. The Fano Effect is the observation of spin polarized photoelectron emission from NONMAGNETIC materials, under chirally selective excitation, such as circularly polarized photons. Within various models, the peak at the Fermi Energy (f{sup 1} peak, quasiparticle peak, Kondo peak) is predicted to be the manifestation of the electrons which shield the otherwise unpaired spin associated with the peak at 2 eV (f{sup 0} peak or Lowermore » Hubbard Band). Utilizing high-energy photoelectron spectroscopy, on and off resonance, the bulk nature and f-character of both features have been confirmed. Thus, observation of phase reversal between the f{sup 0} and f{sup 1} peak is a direct experimental proof of spin shielding in Ce, confirming the original model of Gunnarsson and Shoenhammer, albeit within a Hubbard picture.« less
  • Using Fano effect measurements upon polycrystalline Ce, we have observed a phase reversal between the spectral structure at the Fermi edge and the other 4f derived feature near a binding energy of 2 eV. The Fano effect is the observation of spin polarized photoelectron emission from nonmagnetic materials, under chirally selective excitation, such as circularly polarized photons. The observation of phase reversal between the two peaks is a direct experimental proof of Kondo shielding in Ce, confirming the predictions of Gunnarsson and Shoenhammer, albeit with a small modification.