1,758 research outputs found
Low-Energy Scale Excitations in the Spectral Function of Organic Monolayer Systems
Using high-resolution photoemission spectroscopy we demonstrate that the
electronic structure of several organic monolayer systems, in particular
1,4,5,8-naphthalene tetracarboxylic dianhydride and Copper-phtalocyanine on
Ag(111), is characterized by a peculiar excitation feature right at the Fermi
level. This feature displays a strong temperature dependence and is immediatly
connected to the binding energy of the molecular states, determined by the
coupling between the molecule and the substrate. At low temperatures, the
line-width of this feature, appearing on top of the partly occupied lowest
unoccupied molecular orbital of the free molecule, amounts to only
meV, representing an unusually small energy scale for electronic excitations in
these systems. We discuss possible origins, related e.g. to many-body
excitations in the organic-metal adsorbate system, in particular a generalized
Kondo scenario based on the single impurity Anderson model.Comment: 6 pages, 3 figures, accepted as PRB Rapid Communication
Core hole-electron correlation in coherently coupled molecules
We study the core hole-electron correlation in coherently coupled molecules
by energy dispersive near edge X-ray absorption fine-structure spectroscopy. In
a transient phase, which exists during the transition between two bulk
arrangements, 1,4,5,8-naphthalene-tetracarboxylicacid-dianhydride multilayer
films exhibit peculiar changes of the line shape and energy position of the
X-ray absorption signal at the C K-edge with respect to the bulk and gas phase
spectra. By a comparison to a theoretical model based on a coupling of
transition dipoles, which is established for optical absorption, we demonstrate
that the observed spectroscopic differences can be explained by an
intermolecular delocalized core hole-electron pair. By applying this model we
can furthermore quantify the coherence length of the delocalized core-exciton.Comment: 5 pages, 3 figures, Accepted Version, PRL, minor wording change
Forecasting Wheat and Grass Yields from Climatic Factors
A study of the factors of climate and their relation to wheat and short grass yields was conducted at Hays, Kansas. Statistical correlations were made between the elements of the climate and wheat and short grass yields, also correlations between elements of the climate. A 22-year period was used for forecasting short grass yields and a 30-year period for wheat. In the study, September temperature, spring temperature and spring precipitation, all showed a significant correlation when compared statistically to short grass yields. September temperature was the only element of fall climate that showed a significant amount of correlation when compared to the following year’s grass yields. September temperatures can accurately be used to forecast average short grass production nearly a year prior to harvesting. Spring temperature and spring precipitation accounted for 75 percent of the variability in short grass yields. When comparing September and May soil moisture data to short grass yields, no correlation existed in the study at Hays, Kansas. A highly significant negative correlation existed between temperature and precipitation at Hays, Kansas. Spring temperature, fall precipitation and September precipitation, all showed a significant correlation when compared statistically with wheat production. Fall precipitation, approximately at the time of planting, can accurately be used to forecast average wheat production
Echo of the Quantum Phase Transition of CeCuAu in XPS: Breakdown of Kondo Screening
We present an X-ray photoemission study of the heavy-fermion system
CeCuAu across the magnetic quantum phase transition of this
compound at temperatures above the single-ion Kondo temperature . In
dependence of the Au concentration we observe a sudden change of the
-occupation number and the core-hole potential at the
critical concentration . We interpret these findings in the framework
of the single-impurity Anderson model. Our results are in excellent agreement
with findings from earlier UPS measurements %\cite{klein08qpt} and provide
further information about the precursors of quantum criticality at elevated
temperatures.Comment: 5 pages, 3 figures; published version, references updated, minor
changes in wordin
High-temperature signatures of quantum criticality in heavy fermion systems
We propose a new criterion for distinguishing the Hertz-Millis (HM) and the
local quantum critical (LQC) mechanism in heavy fermion systems with a magnetic
quantum phase transition (QPT). The criterion is based on our finding that the
spin screening of Kondo ions can be completely suppressed by the RKKY coupling
to the surrounding magnetic ions even without magnetic ordering and that,
consequently, the signature of this suppression can be observed in
spectroscopic measurements above the magnetic ordering temperature. We apply
the criterion to high-resolution photoemission (UPS) measurements on
CeCuAu and conclude that the QPT in this system is dominated by
the LQC scenario.Comment: Inveted paper, International Conference on Magnetism, ICM 2009,
Karlsruhe. Published version, added discussions of the relevance of
Fermi-surface fluctuations and of a structural transition near the QC
Momentum-resolved evolution of the Kondo lattice into 'hidden-order' in URu2Si2
We study, using high-resolution angle-resolved photoemission spectroscopy,
the evolution of the electronic structure in URu2Si2 at the Gamma, Z and X
high-symmetry points from the high-temperature Kondo-screened regime to the
low-temperature `hidden-order' (HO) state. At all temperatures and symmetry
points, we find structures resulting from the interaction between heavy and
light bands, related to the Kondo lattice formation. At the X point, we
directly measure a hybridization gap of 11 meV already open at temperatures
above the ordered phase. Strikingly, we find that while the HO induces
pronounced changes at Gamma and Z, the hybridization gap at X does not change,
indicating that the hidden-order parameter is anisotropic. Furthermore, at the
Gamma and Z points, we observe the opening of a gap in momentum in the HO
state, and show that the associated electronic structure results from the
hybridization of a light electron band with the Kondo-lattice bands
characterizing the paramagnetic state.Comment: Updated published version. Mansucript + Supplemental Material (8
pages, 9 figures). Submitted 16 September 201
Structure and transport in multi-orbital Kondo systems
We consider Kondo impurity systems with multiple local orbitals, such as rare
earth ions in a metallic host or multi--level quantum dots coupled to metallic
leads. It is shown that the multiplet structure of the local orbitals leads to
multiple Kondo peaks above the Fermi energy , and to ``shadow'' peaks
below . We use a slave boson mean field theory, which recovers the strong
coupling Fermi liquid fixed point, to calculate the Kondo peak positions,
widths, and heights analytically at T=0, and NCA calculations to fit the
temperature dependence of high--resolution photoemission spectra of Ce
compounds. In addition, an approximate conductance quantization for transport
through multi--level quantum dots or single--atom transistors in the Kondo
regime due to a generalized Friedel sum rule is demonstrated.Comment: 4 pages, 3 figures. Invited article, 23rd International Conference on
Low Temperature Physics LT23, Hiroshima, Japan 200
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