744 research outputs found
Unconventional Anomalous Hall Effect in the Metallic Triangular-Lattice Magnet PdCrO2
We experimentally reveal an unconventional anomalous Hall effect (UAHE) in a
quasi-two-dimensional triangular-lattice antiferromagnet PdCrO2. Using high
quality single crystals of PdCrO2, we found that the Hall resistivity deviates
from the conventional behavior below T* = 20 K, noticeably lower than TN = 37.5
K, at which Cr^{3+} (S=3/2) spins order in a 120 degree structure. In view of
the theoretical expectation that the spin chirality cancels out in the simplest
120 degree spin structure, we discuss required conditions for the emergence of
UAHE within Berry-phase mechanisms.Comment: 4 pages, 5 figures, accepted for publication in PR
Proton radiography to improve proton radiotherapy: Simulation study at different proton beam energies
To improve the quality of cancer treatment with protons, a translation of
X-ray Computed Tomography (CT) images into a map of the proton stopping powers
needs to be more accurate. Proton stopping powers determined from CT images
have systematic uncertainties in the calculated proton range in a patient of
typically 3-4\% and even up to 10\% in region containing
bone~\cite{USchneider1995,USchneider1996,WSchneider2000,GCirrone2007,HPaganetti2012,TPlautz2014,GLandry2013,JSchuemann2014}.
As a consequence, part of a tumor may receive no dose, or a very high dose can
be delivered in healthy ti\-ssues and organs at risks~(e.g. brain
stem)~\cite{ACKnopf2013}. A transmission radiograph of high-energy protons
measuring proton stopping powers directly will allow to reduce these
uncertainties, and thus improve the quality of treatment.
The best way to obtain a sufficiently accurate radiograph is by tracking
individual protons traversing the phantom
(patient)~\cite{GCirrone2007,TPlautz2014,VSipala2013}. In our simulations we
have used an ideal position sensitive detectors measuring a single proton
before and after a phantom, while the residual energy of a proton was detected
by a BaF crystal. To obtain transmission radiographs, diffe\-rent phantom
materials have been irradiated with a 3x3~cm scattered proton beam, with
various beam energies. The simulations were done using the Geant4 simulation
package~\cite{SAgostinelli2003}.
In this study we focus on the simulations of the energy loss radiographs for
various proton beam energies that are clinically available in proton
radiotherapy.Comment: 6 pages, 6 figures, Presented at Jagiellonian Symposium on
Fundamental and Applied Subatomic Physics, 7-12 June, 2015, Krak\'ow, Polan
A generalization of Hausdorff dimension applied to Hilbert cubes and Wasserstein spaces
A Wasserstein spaces is a metric space of sufficiently concentrated
probability measures over a general metric space. The main goal of this paper
is to estimate the largeness of Wasserstein spaces, in a sense to be precised.
In a first part, we generalize the Hausdorff dimension by defining a family of
bi-Lipschitz invariants, called critical parameters, that measure largeness for
infinite-dimensional metric spaces. Basic properties of these invariants are
given, and they are estimated for a naturel set of spaces generalizing the
usual Hilbert cube. In a second part, we estimate the value of these new
invariants in the case of some Wasserstein spaces, as well as the dynamical
complexity of push-forward maps. The lower bounds rely on several embedding
results; for example we provide bi-Lipschitz embeddings of all powers of any
space inside its Wasserstein space, with uniform bound and we prove that the
Wasserstein space of a d-manifold has "power-exponential" critical parameter
equal to d.Comment: v2 Largely expanded version, as reflected by the change of title; all
part I on generalized Hausdorff dimension is new, as well as the embedding of
Hilbert cubes into Wasserstein spaces. v3 modified according to the referee
final remarks ; to appear in Journal of Topology and Analysi
Magnon Dispersion in the Field-Induced Magnetically Ordered Phase of TlCuCl3
The magnetic properties of the interacting dimer system TlCuCl3 are
investigated within a bond-operator formulation. The observed field-induced
staggered magnetic order perpendicular to the field is described as a Bose
condensation of magnons which are linear combinations of dimer singlet and
triplet modes. This technique accounts for the magnetization curve and for the
field dependence of the magnon dispersion curves observed by high-field neutron
scattering measurements.Comment: 4 pages, 4 figures, REVTeX
Cubic lead perovskite PbMoO3 with anomalous metallic behavior
A previously unreported Pb-based perovskite PbMoO is obtained by
high-pressure and high-temperature synthesis. This material crystallizes in the
cubic structure at room temperature, making it distinct from
typical Pb-based perovskite oxides with a structural distortion. PbMoO
exhibits a metallic behavior down to 0.1 K with an unusual -sub linear
dependence of the electrical resistivity. Moreover, a large specific heat is
observed at low temperatures accompanied by a peak in around 10 K, in
marked contrast to the isostructural metallic system SrMoO. These transport
and thermal properties for PbMoO, taking into account anomalously large Pb
atomic displacements detected through diffraction experiments, are attributed
to a low-energy vibrational mode, associated with incoherent off-centering of
lone pair Pb cations. We discuss the unusual behavior of the electrical
resistivity in terms of a polaron-like conduction, mediated by the strong
coupling between conduction electrons and optical phonons of the local
low-energy vibrational mode.Comment: 5 pages, 5 figure
Critical behavior of the metallic triangular-lattice Heisenberg antiferromagnet PdCrO2
We report physical properties of the conductive magnet PdCrO2 consisting of a
layered structure with a triangular lattice of Cr3+ ions (S=3/2). We confirmed
an antiferromagnetic transition at TN=37.5K by means of specific heat,
electrical resistivity, magnetic susceptibility, and neutron scattering
measurements. The critical behavior in the specific heat persists in an
unusually wide temperature range above TN. This fact implies that spin
correlations develop even at much higher temperature than TN. The observed
sub-linear temperature dependence of the resistivity above TN is also
attributed to the short-range correlations among the frustrated spins. While
the critical exponent for the magnetization agrees reasonably with the
prediction of the relevant model, that for the specific heat evaluated in the
wide temperature range differs substantially from the prediction.Comment: 7 pages, 6 figure
Observation of Field-Induced Transverse N\'{e}el Ordering in the Spin Gap System TlCuCl
Neutron elastic scattering experiments have been performed on the spin gap
system TlCuCl in magnetic fields parallel to the -axis. The magnetic
Bragg peaks which indicate the field-induced N\'{e}el ordering were observed
for magnetic field higher than the gap field T at with odd in the plane. The spin structure in the ordered
phase was determined. The temperature and field dependence of the Bragg peak
intensities and the phase boundary obtained were discussed in connection with a
recent theory which describes the field-induced N\'{e}el ordering as a
Bose-Einstein condensation of magnons.Comment: 4 pages, 5 eps figures, jpsj styl
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