86 research outputs found
Hadron masses in QCD with one quark flavour
One-flavour QCD - a gauge theory with SU(3) colour gauge group and a fermion
in the fundamental representation - is studied by Monte Carlo simulations. The
mass spectrum of hadronic bound states is investigated in a volume with
extensions of L ~ 4.4r_0 (~2.2fm) at two different lattice spacings: a ~
0.37r_0 (~0.19fm) and a ~ 0.27r_0 (~0.13fm). The lattice action is Symanzik
tree-level-improved Wilson action for the gauge field and (unimproved) Wilson
action for the fermion.Comment: 21 pages, 4 figures; further references adde
The Kondo Resonance in Electron Spectroscopy
The Kondo resonance is the spectral manifestation of the Kondo properties of
the impurity Anderson model, and also plays a central role in the dynamical
mean-field theory (DMFT) for correlated electron lattice systems. This article
presents an overview of electron spectroscopy studies of the resonance for the
4f electrons of cerium compounds, and for the 3d electrons of V_2O_3, including
beginning efforts at using angle resolved photoemission to determine the
k-dependence of the resonance. The overview includes the comparison and
analysis of spectroscopy data with theoretical spectra as calculated for the
impurity model and as obtained by DMFT, and the Kondo volume collapse
calculation of the cerium alpha-gamma phase transition boundary, with its
spectroscopic underpinnings.Comment: 32 pages, 11 figures, 151 references; paper for special issue of J.
Phys. Soc. Jpn. on "Kondo Effect--40 Years after the Discovery
Photoemission and x-ray absorption spectroscopy study of electron-doped colossal magnetoresistance manganite: La0.7Ce0.3MnO3 film
The electronic structure of La0.7Ce0.3MnO3 (LCeMO) thin film has been
investigated using photoemission spectroscopy (PES) and x-ray absorption
spectroscopy (XAS). The Ce 3d core-level PES and XAS spectra of LCeMO are very
similar to those of CeO2, indicating that Ce ions are far from being trivalent.
A very weak 4f resonance is observed around the Ce 4d 4f absorption edge,
suggesting that the localized Ce 4f states are almost empty in the ground
state. The Mn 2p XAS spectrum reveals the existence of the Mn(2+) multiplet
feature, confirming the Mn(2+)-Mn(3+) mixed-valent states of Mn ions in LCeMO.
The measured Mn 3d PES/XAS spectra for LCeMO agrees reasonably well with the
calculated Mn 3d PDOS using the LSDA+U method. The LSDA+U calculation predicts
a half-metallic ground state for LCeMO.Comment: 7 pages, 7 figure
Dynamical Mean-Field Theory and Its Applications to Real Materials
Dynamical mean-field theory (DMFT) is a non-perturbative technique for the
investigation of correlated electron systems. Its combination with the local
density approximation (LDA) has recently led to a material-specific
computational scheme for the ab initio investigation of correlated electron
materials. The set-up of this approach and its application to materials such as
(Sr,Ca)VO_3, V_2O_3, and Cerium is discussed. The calculated spectra are
compared with the spectroscopically measured electronic excitation spectra. The
surprising similarity between the spectra of the single-impurity Anderson model
and of correlated bulk materials is also addressed.Comment: 20 pages, 9 figures, invited paper for the JPSJ Special Issue "Kondo
Effect - 40 Years after the Discovery"; final version, references adde
The spectral and magnetic properties of - and -Ce from the Dynamical Mean-Field Theory and Local Density Approximation
We have calculated ground state properties and excitation spectra for Ce
metal with the {\it ab initio} computational scheme combining local density
approximation and dynamical mean-field theory (LDA+DMFT). We considered all
electronic states, i.e. correlated f-states and non-correlated s-, p- and
d-states. The strong local correlations (Coulomb interaction) among the
f-states lead to typical many-body resonances in the partial f-density, such as
lower and upper Hubbard band. Additionally the well known Kondo resonance is
observed. The s-, p- and d-densities show small to mediate renormalization
effects due to hybridization. We observe different Kondo temperatures for
- and -Ce ( and
), due to strong volume dependence of the effective
hybridization strength for the localized f-electrons. Finally we compare our
results with a variety of experimental data, i.e. from photoemission
spectroscopy (PES), inverse photoemission spectroscopy (BIS), resonant inverse
photoemission spectroscopy (RIPES) and magnetic susceptibility measurements.Comment: 7 pages, 4 figure
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