1,311 research outputs found
Cascade of magnetic field induced Lifshitz transitions in the ferromagnetic Kondo lattice material YbNi4P2
A ferromagnetic quantum critical point is thought not to exist in two and
three-dimensional metallic systems yet is realized in the Kondo lattice
compound YbNi4(P,As)2, possibly due to its one-dimensionality. It is crucial to
investigate the dimensionality of the Fermi surface of YbNi4P2 experimentally
but common probes such as ARPES and quantum oscillation measurements are
lacking. Here, we studied the magnetic field dependence of transport and
thermodynamic properties of YbNi4P2. The Kondo effect is continuously
suppressed and additionally we identify nine Lifshitz transitions between 0.4
and 18 T. We analyze the transport coefficients in detail and identify the type
of Lifshitz transitions as neck or void type to gain information on the Fermi
surface of YbNi4P2. The large number of Lifshitz transitions observed within
this small energy window is unprecedented and results from the particular flat
renormalized band structure with strong 4f-electron character shaped by the
Kondo lattice effect.Comment: 6 pages, 4 figure
Coupling between magnetic and thermodynamic properties in RhSi ( = Dy, Ho)
Single crystals of DyRhSi and HoRhSi were investigated by
thermal expansion and magnetostriction. The different types of magnetic order
can clearly be seen in these measurements, particularly the canting of the
moments away from the crystallographic direction below about 12~K and the
spin-flip for magnetic field applied along the direction. For
HoRhSi, an additional transition just below is analyzed by
means of the Gr\"{u}neisen ratio and is likely caused by a change of the
magnetic structure. Our results nicely corroborate findings from other magnetic
and thermodynamic measurements on these materials and provide further evidence
suggesting the formation of magnetic domains.Comment: 9 pages, 8 figure
Valence-transition-induced changes of the electronic structure in EuPdSi
We present results of hard X-ray angle-resolved photoemission spectroscopy
and photoemission diffraction measurements performed on high-quality single
crystals of the valence transition compound EuPdSi for temperatures
25~K T 300~K. At low temperatures we observe a Eu valence
, % occupation number , which decreases to for
temperatures above the valence transition around ~K. The
experimental valence numbers resulting from an evaluation of the Eu(III)/Eu(II)
core levels, are used for calculating band structures using density
functional theory. The valence transition significantly changes the band
structure as determined by angle-resolved photoemission spectroscopy. In
particular, the Eu valence bands are shifted to lower binding energies
with increasing Eu occupancy. To a lesser extent, bands derived from the
Si and Pd orbitals are also affected. This observation suggests a
partial charge transfer between Eu and Pd/Si sites. Comparison with {\it
ab-initio} theory shows a good agreement with experiment, in particular
concerning the unequal band shift with increasing Eu occupancy
Feasibility studies of the time-like proton electromagnetic form factor measurements with PANDA at FAIR
The possibility of measuring the proton electromagnetic form factors in the
time-like region at FAIR with the \PANDA detector is discussed. Detailed
simulations on signal efficiency for the annihilation of into a
lepton pair as well as for the most important background channels have been
performed. It is shown that precision measurements of the differential cross
section of the reaction can be obtained in a wide
angular and kinematical range. The individual determination of the moduli of
the electric and magnetic proton form factors will be possible up to a value of
momentum transfer squared of (GeV/c). The total cross section will be measured up to (GeV/c).
The results obtained from simulated events are compared to the existing data.
Sensitivity to the two photons exchange mechanism is also investigated.Comment: 12 pages, 4 tables, 8 figures Revised, added details on simulations,
4 tables, 9 figure
Technical Design Report for the PANDA Solenoid and Dipole Spectrometer Magnets
This document is the Technical Design Report covering the two large
spectrometer magnets of the PANDA detector set-up. It shows the conceptual
design of the magnets and their anticipated performance. It precedes the tender
and procurement of the magnets and, hence, is subject to possible modifications
arising during this process.Comment: 10 pages, 14MB, accepted by FAIR STI in May 2009, editors: Inti
Lehmann (chair), Andrea Bersani, Yuri Lobanov, Jost Luehning, Jerzy Smyrski,
Technical Coordiantor: Lars Schmitt, Bernd Lewandowski (deputy),
Spokespersons: Ulrich Wiedner, Paola Gianotti (deputy
Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR
Simulation results for future measurements of electromagnetic proton form
factors at \PANDA (FAIR) within the PandaRoot software framework are reported.
The statistical precision with which the proton form factors can be determined
is estimated. The signal channel is studied on the basis
of two different but consistent procedures. The suppression of the main
background channel, , is studied.
Furthermore, the background versus signal efficiency, statistical and
systematical uncertainties on the extracted proton form factors are evaluated
using two different procedures. The results are consistent with those of a
previous simulation study using an older, simplified framework. However, a
slightly better precision is achieved in the PandaRoot study in a large range
of momentum transfer, assuming the nominal beam conditions and detector
performance
Search for the decay
We search for radiative decays into a weakly interacting neutral
particle, namely an invisible particle, using the produced through the
process in a data sample of
decays collected by the BESIII detector
at BEPCII. No significant signal is observed. Using a modified frequentist
method, upper limits on the branching fractions are set under different
assumptions of invisible particle masses up to 1.2 . The upper limit corresponding to an invisible particle with zero mass
is 7.0 at the 90\% confidence level
- …