229 research outputs found
Fermi volume evolution and crystal field excitations in heavy-fermion compounds probed by time-domain terahertz spectroscopy
We measure the quasiparticle weight in the heavy-fermion compound
CeCuAu () by time-resolved THz spectroscopy for
temperatures from 2 up to 300\,K. This method distinguishes contributions from
the heavy Kondo band and from the crystal-electric-field satellite bands by
different THz response delay times. We find that the formation of heavy bands
is controlled by an exponentially enhanced, high-energy Kondo scale once the
crystal-electric-field states become thermally occupied. We corroborate these
observations by temperature-dependent dynamical mean-field calculations for the
multi-orbital Anderson lattice model and discuss consequences for quantum
critical scenarios.Comment: Published version, 6 pages (including references), 5 figures,
Supplemental Material (2 pages) adde
Mott--Hubbard transition vs. Anderson localization of correlated, disordered electrons
The phase diagram of correlated, disordered electrons is calculated within
dynamical mean--field theory using the geometrically averaged (''typical'')
local density of states. Correlated metal, Mott insulator and Anderson
insulator phases, as well as coexistence and crossover regimes are identified.
The Mott and Anderson insulators are found to be continuously connected.Comment: 4 pages, 4 figure
Pronounced Diurnal Pattern of Salivary C-Reactive Protein (CRP) With Modest Associations to Circulating CRP Levels
C-reactive protein (CRP), a humoral component of the innate immune system with important
functions in host-defense, is extensively used as a sensitive biomarker of systemic
inflammation. During inflammation, hepatocyte-derived CRP rises dramatically in the blood
due to increased interleukin-6 (IL-6) levels. Reliable detection of CRP in saliva, instead of
blood, would offer advantages regarding sampling procedure and availability but using saliva
as a diagnostic body fluid comes with challenges. The aims of this study were to evaluate
associations between salivary CRP, total protein levels in saliva and serum CRP. Furthermore,
we examined associations with plasma IL-6, body mass index (BMI), tobacco smoking and
age. Salivary CRP was investigated by ELISA in 107 middle-aged participants from the
general population. We employed spectrophotometric determination of total protein levels.
Correlation analyses were used for associations of salivary CRP with serum CRP
(turbidimetry), plasma IL-6 (LuminexÂź), BMI and smoking habits. Salivary median CRP was
68% higher (p=0.009), and total protein levels were 167% higher (p<0.0001), in morning
compared to evening saliva. The correlation coefficients between serum and salivary CRP
were low to moderate, but stronger for evening than morning saliva. Plasma IL-6 correlated
significantly with serum CRP (rs=0.41, p<0.01), but not with morning or evening salivary CRP.
Non-smokers showed 103% higher salivary CRP levels (p=0.015), whereas serum CRP was
independent of smoking status. As opposed to CRP in serum, salivary CRP was not
associated with BMI. Salivary CRP was 90% higher among the age interval 60â69 years
compared to subjects aged 45â59 (p=0.02) while serum CRP levels did not differ between the
age groups. In conclusion, CRP in saliva did not straightforwardly reflect serum
concentrations. This raises questions regarding adequate reflection of biological events.
The pronounced diurnal salivary CRP pattern accentuates the importance of standardizing
the time-point of sampling
Theories of non-Fermi liquid behavior in heavy fermions
I review our incomplete understanding of non-Fermi liquid behavior in heavy
fermion systems at a quantum critical point. General considerations suggest
that critical antiferromagnetic fluctuations do not destroy the Fermi surface
by scattering the heavy electrons- but by actually breaking up the internal
structure of the heavy fermion. I contrast the weak, and strong-coupling view
of the quantum phase transition, emphasizing puzzles and questions that recent
experiments raise.Comment: Overview talk, SCES Paris 1998. References to Sachdev and Ye adde
muSR and NMR in f-electron non-Fermi liquid materials
Magnetic resonance (muSR and NMR) studies of f-electron non-Fermi-liquid
(NFL) materials give clear evidence that structural disorder is a major factor
in NFL behavior. Longitudinal-field muSR relaxation measurements at low fields
reveal a wide distribution of muon relaxation rates and divergences in the
frequency dependence of spin correlation functions in the NFL systems
UCu_{5-x}Pd_x and CePtSi_{1-x}Ge_x. These divergences seem to be due to slow
dynamics associated with quantum spin-glass behavior, rather than quantum
criticality as in a uniform system, for two reasons: the observed strong
inhomogeneity in the muon relaxation rate, and the strong and
frequency-dependent low-frequency fluctuation observed in U(Cu,Pd)_5 and
CePt(Si,Ge). In the NFL materials CeCu_{5.9}Au_{0.1},
Ce(Ru_{0.5}Rh_{0.5})_2Si_2, CeNi_2Ge_2, and YbRh_2Si_2 the low-frequency weight
of the spin fluctuation spectrum is much weaker than in the disordered NFL
systems.Comment: 10 pages, 4 figures. To be published in proceedings of muSR2002
(Physica B
Finite temperature strong-coupling expansions for the Kondo lattice model
Strong-coupling expansions, to order , are derived for the Kondo
lattice model of strongly correlated electrons, in 1-, 2- and 3- dimensions at
arbitrary temperature. Results are presented for the specific heat, and spin
and charge susceptibilities.Comment: revtex
Pauli spin susceptibility of a strongly correlated two-dimensional electron liquid
Thermodynamic measurements reveal that the Pauli spin susceptibility of
strongly correlated two-dimensional electrons in silicon grows critically at
low electron densities - behavior that is characteristic of the existence of a
phase transition.Comment: As publishe
Non-Fermi-liquid behavior in the Kondo lattices induced by peculiarities of magnetic ordering and spin dynamics
A scaling consideration of the Kondo lattices is performed with account of
singularities in the spin excitation spectral function. It is shown that a
non-Fermi-liquid (NFL) behavior between two critical values of the bare
coupling constant occurs naturally for complicated magnetic structures with
several magnon branches. This may explain the fact that a NFL behavior takes
place often in the heavy-fermion systems with peculiar spin dynamics. Another
kind of a NFL-like state (with different critical exponents) can occur for
simple antiferromagnets with account of magnon damping, and for paramagnets,
especially with two-dimensional character of spin fluctuations. The mechanisms
proposed lead to some predictions about behavior of specific heat, resistivity,
magnetic susceptibility, and anisotropy parameter, which can be verified
experimentally.Comment: 16 pages, RevTeX, 4 Postscript figures. Extended versio
Tailoring supercurrent confinement in graphene bilayer weak links
The Josephson effect is one of the most studied macroscopic quantum phenomena
in condensed matter physics and has been an essential part of the quantum
technologies development over the last decades. It is already used in many
applications such as magnetometry, metrology, quantum computing, detectors or
electronic refrigeration. However, developing devices in which the induced
superconductivity can be monitored, both spatially and in its magnitude,
remains a serious challenge. In this work, we have used local gates to control
confinement, amplitude and density profile of the supercurrent induced in
one-dimensional nanoscale constrictions, defined in bilayer graphene-hexagonal
boron nitride van der Waals heterostructures. The combination of resistance
gate maps, out-of-equilibrium transport, magnetic interferometry measurements,
analytical and numerical modelling enables us to explore highly tunable
superconducting weak links. Our study opens the path way to design more complex
superconducting circuits based on this principle such as electronic
interferometers or transition-edge sensors
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