1,048 research outputs found
Kohn anomalies in momentum dependence of magnetic susceptibility of some three-dimensional systems
We study a question of presence of Kohn points, yielding at low temperatures
non-analytic momentum dependence of magnetic susceptibility near its maximum,
in electronic spectum of some three-dimensional systems. In particular, we
consider one-band model on face centered cubic lattice with hopping between
nearest and next-nearest neighbors, which models some aspects of the dispersion
of ZrZn, and the two-band model on body centered cubic lattice, modeling
the dispersion of chromium. For the former model it is shown that Kohn points
yielding maxima of susceptibility exist in a certain (sufficiently wide) region
of electronic concentrations; the dependence of the wave vectors, corresponding
to the maxima, on the chemical potential is investigated. For the two-band
model we show existence of the lines of Kohn points, yielding maximum of the
susceptibility, which position agrees with the results of band structure
calculations and experimental data on the wave vector of antiferromagnetism of
chromium.Comment: 13 pages, 9 figures. JETP, in press (2017
Highly mobile carriers in orthorhombic phases of iron-based superconductors FeSeS
The field and temperature dependencies of the longitudinal and Hall
resistivity have been measured for FeSeS (x=0.04, 0.09 and
0.19) single crystals. The sample FeSeS does not show a
transition to an orthorhombic phase and exhibits at low temperatures the
transport properties quite different from those of orthorhombic samples. The
behavior of FeSeS is well described by the simple two
band model with comparable values of hole and electron mobility. In particular,
at low temperatures the transverse resistance shows a linear field dependence,
the magnetoresistance follow a quadratic field dependence and obeys to Kohler's
rule. In contrast, Kohler's rule is strongly violated for samples having an
orthorhombic low temperature structure. However, the transport properties of
the orthorhombic samples can be satisfactory described by the three band model
with the pair of almost equivalent to the tetragonal sample hole and electron
bands, supplemented with the highly mobile electron band which has two order
smaller carrier number. Therefore, the peculiarity of the low temperature
transport properties of the orthorhombic Fe(SeS) samples, as probably of many
other orthorhombic iron superconductors, is due to the presence of a small
number of highly mobile carriers which originate from the local regions of the
Fermi surface, presumably, nearby the Van Hove singularity points
Hybridization and spin-orbit coupling effects in quasi-one-dimensional spin-1/2 magnet Ba3Cu3Sc4O12
We study electronic and magnetic properties of the quasi-one-dimensional
spin-1/2 magnet Ba3Cu3Sc4O12 with a distinct orthogonal connectivity of CuO4
plaquettes. An effective low-energy model taking into account spin-orbit
coupling was constructed by means of first-principles calculations. On this
basis a complete microscopic magnetic model of Ba3Cu3Sc4O12, including
symmetric and antisymmetric anisotropic exchange interactions, is derived. The
anisotropic exchanges are obtained from a distinct first-principles numerical
scheme combining, on one hand, the local density approximation taking into
account spin-orbit coupling, and, on the other hand, projection procedure along
with the microscopic theory by Toru Moriya. The resulting tensors of the
symmetric anisotropy favor collinear magnetic order along the structural chains
with the leading ferromagnetic coupling J1 = -9.88 meV. The interchain
interactions J8 = 0.21 meV and J5 = 0.093 meV are antiferromagnetic. Quantum
Monte Carlo simulations demonstrated that the proposed model reproduces the
experimental Neel temperature, magnetization and magnetic susceptibility data.
The modeling of neutron diffraction data reveals an important role of the
covalent Cu-O bonding in Ba3Cu3Sc4O12.Comment: 11 pages, 12 figure
Magnetotransport properties of FeSe in fields up to 50T
Magnetotransport properties of the high-quality FeSe crystal, measured in a
wide temperature range and in magnetic fields up to 50 T, show the symmetry of
the main holelike and electronlike bands in this compound. In addition to the
main two bands, there is also a tiny, highly mobile, electronlike band which is
responsible for the non-linear behavior of (B) at low temperatures
and some other peculiarities of FeSe. We observe the inversion of the
temperature coeficient at a magnetic field higher than about 20 T
which is an implicit conformation of the electron-hole symmetry in the main
bands.Comment: MISM 201
Physics Reach of High-Energy and High-Statistics IceCube Atmospheric Neutrino Data
This paper investigates the physics reach of the IceCube neutrino detector
when it will have collected a data set of order one million atmospheric
neutrinos with energies in the 0.1 \sim 10^4 TeV range. The paper consists of
three parts. We first demonstrate how to simulate the detector performance
using relatively simple analytic methods. Because of the high energies of the
neutrinos, their oscillations, propagation in the Earth and regeneration due to
\tau decay must be treated in a coherent way. We set up the formalism to do
this and discuss the implications. In a final section we apply the methods
developed to evaluate the potential of IceCube to study new physics beyond
neutrino oscillations. Not surprisingly, because of the increased energy and
statistics over present experiments, existing bounds on violations of the
equivalence principle and of Lorentz invariance can be improved by over two
orders of magnitude. The methods developed can be readily applied to other
non-conventional physics associated with neutrinos.Comment: 21 pages, 7 figures, Revtex
Majority carrier type inversion in FeSe family and "doped semimetal" scheme in iron-based superconductors
The field and temperature dependencies of the longitudinal and Hall
resistivity have been studied for high-quality FeSeS (x up to
0.14) single crystals. Quasiclassical analysis of the obtained data indicates a
strong variation of the electron and hole concentrations under the studied
isovalent substitution and proximity of FeSe to the point of the majority
carrier-type inversion. On this basis, we propose a `doped semimetal' scheme
for the superconducting phase diagram of the FeSe family, which can be applied
to other iron-based superconductors. In this scheme, the two local maxima of
the superconducting temperature can be associated with the Van Hove
singularities of a simplified semi-metallic electronic structure. The
multicarrier analysis of the experimental data also reveals the presence of a
tiny and highly mobile electron band for all the samples studied. Sulfur
substitution in the studied range leads to a decrease in the number of mobile
electrons by more than ten times, from about 3\% to about 0.2\%. This behavior
may indicate a successive change of the Fermi level position relative to
singular points of the electronic structure which is consistent with the `doped
semimetal' scheme. The scattering time for mobile carriers does not depend on
impurities, which allows us to consider this group as a possible source of
unusual acoustic properties of FeSe
Dynamical lattice instability versus spin liquid state in a frustrated spin chain system
The low-dimensional s=1/2 compound (NO)[Cu(NO3)3] has recently been suggested
to follow the Nersesyan-Tsvelik model of coupled spin chains. Such a system
shows unbound spinon excitations and a resonating valence bond ground state due
spin frustration. Our Raman scattering study demonstrates phonon anomalies as
well as the suppression of a broad magnetic scattering continuum for
temperatures below a characteristic temperature, T<T*=100K. We interpret these
effects as evidence for a dynamical interplay of spin and lattice degrees of
freedom that might lead to a further transition into a dimerized or
structurally distorted phase at lower temperatures.Comment: 5 pages, 6 figure
Radiography of the Earth's Core and Mantle with Atmospheric Neutrinos
A measurement of the absorption of neutrinos with energies in excess of 10
TeV when traversing the Earth is capable of revealing its density distribution.
Unfortunately, the existence of beams with sufficient luminosity for the task
has been ruled out by the AMANDA South Pole neutrino telescope. In this letter
we point out that, with the advent of second-generation kilometer-scale
neutrino detectors, the idea of studying the internal structure of the Earth
may be revived using atmospheric neutrinos instead.Comment: 4 pages, LaTeX file using RevTEX4, 2 figures and 1 table included.
Matches published versio
Signatures of cosmic tau-neutrinos
The importance and signatures of cosmic tau--(anti)neutrinos have been
studied for upward-- and downward--going and hadronic shower
event rates relevant for present and future underground water or ice detectors,
utilizing the unique and reliable ultrasmall-- predictions of the dynamical
(radiative) parton model. The upward--going event rates
calculated just from cosmic fluxes are sizeably
enhanced by taking into account cosmic fluxes
and their associated fluxes as well. The coupled transport
equations for the upward--going flux traversing
the Earth imply an enhancement of the attenuated and regenerated
flux typically around GeV with respect
to the initial cosmic flux. This enhancement turns out to be smaller than
obtained so far, in particular for flatter initial cosmic fluxes behaving like
. Downward--going events and in particular the
background--free and unique hadronic `double bang' and `lollipop' events allow
to test downward--going cosmic fluxes up to
about GeV.Comment: 32 pages, 6 figures; Added reference
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