28,427 research outputs found
Anisotropic Electronic Structure of the Kondo Semiconductor CeFe2Al10 Studied by Optical Conductivity
We report temperature-dependent polarized optical conductivity
[] spectra of CeFeAl, which is a reference material
for CeRuAl and CeOsAl with an anomalous magnetic
transition at 28 K. The spectrum along the b-axis differs
greatly from that in the -plane, indicating that this material has an
anisotropic electronic structure. At low temperatures, in all axes, a shoulder
structure due to the optical transition across the hybridization gap between
the conduction band and the localized states, namely -
hybridization, appears at 55 meV. However, the gap opening temperature and the
temperature of appearance of the quasiparticle Drude weight are strongly
anisotropic indicating the anisotropic Kondo temperature. The strong
anisotropic nature in both electronic structure and Kondo temperature is
considered to be relevant the anomalous magnetic phase transition in
CeRuAl and CeOsAl.Comment: 5 pages, 4 figure
Observation of an optical non-Fermi-liquid behavior in the heavy fermion state of YbRhSi
We report far-infrared optical properties of YbRhSi for photon
energies down to 2 meV and temperatures 0.4 -- 300 K. In the coherent heavy
quasiparticle state, a linear dependence of the low-energy scattering rate on
both temperature and photon energy was found. We relate this distinct dynamical
behavior different from that of Fermi liquid materials to the non-Fermi liquid
nature of YbRhSi which is due to its close vicinity to an
antiferromagnetic quantum critical point.Comment: 5 pages, 4 figures. submitte
Electronic-Structure-Driven Magnetic Ordering in a Kondo Semiconductor CeOs2Al10
We report the anisotropic changes in the electronic structure of a Kondo
semiconductor CeOsAl across an anomalous antiferromagnetic ordering
temperature () of 29 K, using optical conductivity spectra. The spectra
along the - and -axes indicate that a - hybridization gap emerges
from a higher temperature continuously across . Along the b-axis, on the
other hand, a different energy gap with a peak at 20 meV appears below 39 K,
which is higher temperature than , because of structural distortion. The
onset of the energy gap becomes visible below . Our observation reveals
that the electronic structure as well as the energy gap opening along the
b-axis due to the structural distortion induces antiferromagnetic ordering
below .Comment: 4 pages, 4 figure
Stochastic delocalization of finite populations
Heterogeneities in environmental conditions often induce corresponding
heterogeneities in the distribution of species. In the extreme case of a
localized patch of increased growth rates, reproducing populations can become
strongly concentrated at the patch despite the entropic tendency for population
to distribute evenly. Several deterministic mathematical models have been used
to characterize the conditions under which localized states can form, and how
they break down due to convective driving forces. Here, we study the
delocalization of a finite population in the presence of number fluctuations.
We find that any finite population delocalizes on sufficiently long time
scales. Depending on parameters, however, populations may remain localized for
a very long time. The typical waiting time to delocalization increases
exponentially with both population size and distance to the critical wind speed
of the deterministic approximation. We augment these simulation results by a
mathematical analysis that treats the reproduction and migration of individuals
as branching random walks subject to global constraints. For a particular
constraint, different from a fixed population size constraint, this model
yields a solvable first moment equation. We find that this solvable model
approximates very well the fixed population size model for large populations,
but starts to deviate as population sizes are small. The analytical approach
allows us to map out a phase diagram of the order parameter as a function of
the two driving parameters, inverse population size and wind speed. Our results
may be used to extend the analysis of delocalization transitions to different
settings, such as the viral quasi-species scenario
Limitations on the extent of off-center displacements in TbMnO3 from EXAFS measurements
We present EXAFS data at the Mn K and Tb L3 edges that provide upper limits
on the possible displacements of any atoms in TbMnO3. The displacements must be
less than 0.005-0.01A for all atoms which eliminates the possibility of
moderate distortions (0.02A) with a small c-axis component, but for which the
displacements in the ab plane average to zero. Assuming the polarization arises
from a displacement of the O2 atoms along the c-axis, the measured polarization
then leads to an O2 displacement that is at least 6X10^{-4}A, well below our
experimental limit. Thus a combination of the EXAFS and the measured electrical
polarization indicate that the atomic displacements likely lie in the range
6X10^{-4} - 5X10^{-3}A.Comment: submitted to PRB; 11 pages (preprint form) 7 figure
Nucleation for one-dimensional long-range Ising models
In this note we study metastability phenomena for a class of long-range Ising
models in one-dimension. We prove that, under suitable general conditions, the
configuration -1 is the only metastable state and we estimate the mean exit
time. Moreover, we illustrate the theory with two examples (exponentially and
polynomially decaying interaction) and we show that the critical droplet can be
macroscopic or mesoscopic, according to the value of the external magnetic
field.Comment: 15 pages, 3 figure
Temperature- and Magnetic-Field-Dependent Optical Properties of Heavy Quasiparticles in YbIr2Si2
We report the temperature- and magnetic-field-dependent optical conductivity
spectra of the heavy electron metal YbIrSi. Upon cooling below the
Kondo temperature (), we observed a typical charge dynamics that is
expected for a formation of a coherent heavy quasiparticle state. We obtained a
good fitting of the Drude weight of the heavy quasiparticles by applying a
modified Drude formula with a photon energy dependence of the quasiparticle
scattering rate that shows a similar power-law behavior as the temperature
dependence of the electrical resistivity. By applying a magnetic field of 6T
below , we found a weakening of the effective dynamical mass
enhancement by about 12% in agreement with the expected decrease of the
-conduction electron hybridization on magnetic field.Comment: 5 pages, 4 figures. to be published in Journal of the Physical
Society of Japan Vol. 79 (2010) No. 1
Quasi-particle scattering and protected nature of topological states in a parent topological insulator BiSe
We report on angle resolved photoemission spectroscopic studies on a parent
topological insulator (TI), BiSe. The line width of the spectral
function (inverse of the quasi-particle lifetime) of the topological metallic
(TM) states shows an anomalous behavior. This behavior can be reasonably
accounted for by assuming decay of the quasi-particles predominantly into bulk
electronic states through electron-electron interaction and defect scattering.
Studies on aged surfaces reveal that topological metallic states are very much
unaffected by the potentials created by adsorbed atoms or molecules on the
surface, indicating that topological states could be indeed protected against
weak perturbations.Comment: accepted for publication in Phys. Rev. B(R
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