230 research outputs found
Crystal-fields in YbInNi4 determined with magnetic form factor and inelastic neutron scattering
The magnetic form factor of YbInNi4 has been determined via the flipping
ratios R with polarized neutron diffraction and the scattering function S(Q,w)
was measured in an inelastic neutron scattering experiment. Both experiments
were performed with the aim to determine the crystal-field scheme. The magnetic
form factor clearly excludes the possibility of a \Gamma7 doublet as the ground
state. The inelastic neutron data exhibit two, almost equally strong peaks at
3.2 meV and 4.4 meV which points, in agreement with earlier neutron data,
towards a \Gamma8 quartet ground state. Further possibilities like a
quasi-quartet ground state are discussed.Comment: 7 pages, 5 figures, 2 tables, submitted to PR
Quantitative study of valence and configuration interaction parameters of the Kondo semiconductors CeM2Al10 (M = Ru, Os and Fe) by means of bulk-sensitive hard x-ray photoelectron spectroscopy
The occupancy of the 4f^n contributions in the Kondo semiconductors
CeM2Al10(M = Ru, Os and Fe) has been quantitatively determined by means of
bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES) on the Ce 3d core
levels. Combining a configuration interaction scheme with full multiplet
calculations allowed to accurately describe the HAXPES data despite the
presence of strong plasmon excitations in the spectra. The configuration
interaction parameters obtained from this analysis -- in particular the
hybridization strength V_eff and the effective f binding energy Delta_f --
indicate a slightly stronger exchange interaction in CeOs2Al10 compared to
CeRu2Al10, and a significant increase in CeFe2Al10. This verifies the
coexistence of a substantial amount of Kondo screening with magnetic order and
places the entire CeM2Al10 family in the region of strong exchange
interactions.Comment: 9 pages, 4 figures, submitted to Physical Review
Determining the crystal-field ground state in rare earth Heavy Fermion materials using soft-x-ray absorption spectroscopy
We infer that soft-x-ray absorption spectroscopy is a versatile method for
the determination of the crystal-field ground state symmetry of rare earth
Heavy Fermion systems, complementing neutron scattering. Using realistic and
universal parameters, we provide a theoretical mapping between the polarization
dependence of Ce spectra and the charge distribution of the Ce
states. The experimental resolution can be orders of magnitude larger than the
crystal field splitting itself. To demonstrate the experimental
feasibility of the method, we investigated CePdSi, thereby settling an
existing disagreement about its crystal-field ground state
CeRuSn: a strongly correlated material with nontrivial topology
Topological insulators form a novel state of matter that provides new
opportunities to create unique quantum phenomena. While the materials used so
far are based on semiconductors, recent theoretical studies predict that also
strongly correlated systems can show non-trivial topological properties,
thereby allowing even the emergence of surface phenomena that are not possible
with topological band insulators. From a practical point of view, it is also
expected that strong correlations will reduce the disturbing impact of defects
or impurities, and at the same increase the Fermi velocities of the topological
surface states. The challenge is now to discover such correlated materials.
Here, using advanced x-ray spectroscopies in combination with band structure
calculations, we infer that CeRuSn is a strongly correlated material
with non-trivial topology.Comment: 10 pages, 6 figures, submitted to Scientific Report
Slow crossover in YbXCu4 intermediate valence compounds
We compare the results of measurements of the magnetic susceptibility Chi(T),
the linear coefficient of specific heat Gamma(T)=C(T)/T and 4f occupation
number nf(T) for the intermediate valence compounds YbXCu4 (X = Ag, Cd, In, Mg,
Tl, Zn) to the predictions of the Anderson impurity model, calculated in the
non-crossing approximation (NCA). The crossover from the low temperature Fermi
liquid state to the high temperature local moment state is substantially slower
in the compounds than predicted by the NCA; this corresponds to the
''protracted screening'' recently predicted for the Anderson Lattice. We
present results for the dynamic susceptibility, measured through neutron
scattering experiments, to show that the deviations between theory and
experiment are not due to crystal field effects, and we present
x-ray-absorption fine-structure (XAFS) results that show the local crystal
structure around the X atoms is well ordered, so that the deviations probably
do not arise from Kondo Disorder. The deviations may correlate with the
background conduction electron density, as predicted for protracted screening.Comment: Submitted to Physical Review B on June 7, 2000, accepted for
publication November 2, 2000. Changes to the original manuscript include: 1)
a discussion of the relation of the slow crossover to the conduction electron
density; 2) a discussion of the relation of the reported results to earlier
photoemission results; and, 3) minor editorial change
PIF4 enhances DNA binding by CDF2 to co-regulate target gene expression and promote Arabidopsis hypocotyl cell elongation
How specificity is conferred within gene regulatory networks is an important problem in biology. The basic helix–loop–helix PHYTOCHROME-INTERACTING FACTORs (PIFs) and single zinc-finger CYCLING DOF FACTORs (CDFs) mediate growth responses of Arabidopsis to light and temperature. We show that these two classes of transcription factor (TF) act cooperatively. CDF2 and PIF4 are temporally and spatially co-expressed, they interact to form a protein complex and act in the same genetic pathway to promote hypocotyl cell elongation. Furthermore, PIF4 substantially strengthens genome-wide occupancy of CDF2 at a subset of its target genes. One of these, YUCCA8, encodes an auxin biosynthesis enzyme whose transcription is increased by PIF4 and CDF2 to contribute to hypocotyl elongation. The binding sites of PIF4 and CDF2 in YUCCA8 are closely spaced, and in vitro PIF4 enhances binding of CDF2. We propose that this occurs by direct protein interaction and because PIF4 binding alters DNA conformation. Thus, we define mechanisms by which PIF and CDF TFs cooperate to achieve regulatory specificity and promote cell elongation in response to light
Crystal-field ground state of the non-centrosymmetric superconductor CePt3Si: a combined polarized soft X-ray absorption and polarized neutron study
We determined the crystal-field split Hund's rule ground state of the
non-centrosymmetric heavy fermion superconductor CePt3Si with polarization
dependent soft X-ray absorption spectroscopy (XAS) and polarized neutron
scattering. We are also able to give the sequence of the crystal-field states
from the temperature evolution of the linear dichroic signal in the XAS. The
quantitative analysis of the XAS temperature dependence together with the
neutron transition energies complete the identification of the crystal-field
level scheme.Comment: 6 pages, 5 figures, submitted to PR
Antiferromagnetic correlations in strongly valence fluctuating CeIrSn
CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a
strongly valence fluctuating compound, as we confirm by hard x-ray
photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo
temperature of \,K. We report a negative in-plane
thermal expansion below 2\,K, which passes through a broad minimum
near 0.75\,K. Volume and -axis magnetostriction for are
markedly negative at low fields and change sign before a sharp metamagnetic
anomaly at 6\,T. These behaviors are unexpected for Ce-based intermediate
valence systems, which should feature positive expansivity. Rather they point
towards antiferromagnetic correlations at very low temperatures. This is
supported by muon spin relaxation measurements down to 0.1\,K, which provide
microscopic evidence for a broad distribution of internal magnetic fields.
Comparison with isostructural CeRhSn suggests that these antiferromagnetic
correlations emerging at result from geometrical
frustration.Comment: to be published in Phys. Rev. Let
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