836 research outputs found
Simultaneously optimizing the interdependent thermoelectric parameters in Ce(NiCu)Al
Substitution of Cu for Ni in the Kondo lattice system CeNiAl results
in a simultaneous optimization of the three interdependent thermoelectric
parameters: thermoelectric power, electrical and thermal conductivities, where
the electronic change in conduction band induced by the extra electron of Cu is
shown to be crucial. The obtained thermoelectric figure of merit amounts
to 0.125 at around 100 K, comparable to the best values known for Kondo
compounds. The realization of ideal thermoelectric optimization in
Ce(NiCu)Al indicates that proper electronic tuning of Kondo
compounds is a promising approach to efficient thermoelectric materials for
cryogenic application.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review
Kondo Insulator to Semimetal Transformation Tuned by Spin-Orbit Coupling
Recent theoretical studies of topologically nontrivial electronic states in
Kondo insulators have pointed to the importance of spin-orbit coupling (SOC)
for stabilizing these states. However, systematic experimental studies that
tune the SOC parameter in Kondo insulators remain elusive.
The main reason is that variations of (chemical) pressure or doping strongly
influence the Kondo coupling and the chemical potential --
both essential parameters determining the ground state of the material -- and
thus possible tuning effects have remained unnoticed. Here
we present the successful growth of the substitution series
CeBi(PtPd) () of the archetypal
(noncentrosymmetric) Kondo insulator CeBiPt. The Pt-Pd substitution
is isostructural, isoelectronic, and isosize, and therefore likely to leave
and essentially unchanged. By contrast, the large mass
difference between the element Pt and the element Pd leads to a large
difference in , which thus is the dominating tuning
parameter in the series. Surprisingly, with increasing (decreasing
), we observe a Kondo insulator to semimetal transition,
demonstrating an unprecedented drastic influence of the SOC. The fully
substituted end compound CeBiPd shows thermodynamic signatures of a
recently predicted Weyl-Kondo semimetal.Comment: 6 pages, 5 figures plus Supplemental Materia
Thermoelectric transport through strongly correlated quantum dots
The thermoelectric properties of strongly correlated quantum dots, described
by a single level Anderson model coupled to conduction electron leads, is
investigated using Wilson's numerical renormalization group method. We
calculate the electronic contribution, , to the thermal conductance,
the thermopower, , and the electrical conductance, , of a quantum dot as
a function of both temperature, , and gate voltage, , for strong,
intermediate and weak Coulomb correlations, , on the dot. For strong
correlations and in the Kondo regime, we find that the thermopower exhibits two
sign changes, at temperatures and with
. Such sign changes in are particularly sensitive
signatures of strong correlations and Kondo physics. The relevance of this to
recent thermopower measurements of Kondo correlated quantum dots is discussed.
We discuss the figure of merit, power factor and the degree of violation of the
Wiedemann-Franz law in quantum dots. The extent of temperature scaling in the
thermopower and thermal conductance of quantum dots in the Kondo regime is also
assessed.Comment: 21 pages, 12 figures; published versio
Anisotropic optical conductivity of the putative Kondo insulator CeRuSn
Kondo insulators and in particular their non-cubic representatives have
remained poorly understood. Here we report on the development of an anisotropic
energy pseudogap in the tetragonal compound CeRuSn employing optical
reflectivity measurements in broad frequency and temperature ranges, and local
density approximation plus dynamical mean field theory calculations. The
calculations provide evidence for a Kondo insulator-like response within the
plane and a more metallic response along the c axis and qualitatively
reproduce the experimental observations, helping to identify their origin
How to identify and characterize strongly correlated topological semimetals
How strong correlations and topology interplay is a topic of great current
interest. In this perspective paper, we focus on correlation-driven gapless
phases. We take the time-reversal symmetric Weyl semimetal as an example
because it is expected to have clear (albeit nonquantized) topological
signatures in the Hall response and because the first strongly correlated
representative, the noncentrosymmetric Weyl-Kondo semimetal CeBiPd,
has recently been discovered. We summarize its key characteristics and use them
to construct a prototype Weyl-Kondo semimetal temperature-magnetic field phase
diagram. This allows for a substantiated assessment of other Weyl-Kondo
semimetal candidate materials. We also put forward scaling plots of the
intrinsic Berry-curvature-induced Hall response vs the inverse Weyl velocity --
a measure of correlation strength, and vs the inverse charge carrier
concentration -- a measure of the proximity of Weyl nodes to the Fermi level.
They suggest that the topological Hall response is maximized by strong
correlations and small carrier concentrations. We hope that our work will guide
the search for new Weyl-Kondo semimetals and correlated topological semimetals
in general, and also trigger new theoretical work.Comment: 22 pages, 5 figures, 2 table
Modelling the incomplete Paschen-Back effect in the spectra of magnetic Ap stars
We present first results of a systematic investigation of the incomplete
Paschen-Back effect in magnetic Ap stars. A short overview of the theory is
followed by a demonstration of how level splittings and component strengths
change with magnetic field strength for some lines of special astrophysical
interest. Requirements are set out for a code which allows the calculation of
full Stokes spectra in the Paschen-Back regime and the behaviour of Stokes I
and V profiles of transitions in the multiplet 74 of FeII is discussed in some
detail. It is shown that the incomplete Paschen-Back effect can lead to
noticeable line shifts which strongly depend on total multiplet strength,
magnetic field strength and field direction. Ghost components (which violate
the normal selection rule on J) show up in strong magnetic fields but are
probably unobservable. Finally it is shown that measurements of the integrated
magnetic field modulus are not adversely affected by the Paschen-Back
effect, and that there is a potential problem in (magnetic) Doppler mapping if
lines in the Paschen-Back regime are treated in the Zeeman approximation.Comment: 8 pages, 10 figures, to appear in MNRA
- …