4,880 research outputs found
Field-theory calculation of the electric dipole moment of the neutron and paramagnetic atoms
Electric dipole moments (edms) of bound states that arise from the
constituents having edms are studied with field-theoretic techniques. The
systems treated are the neutron and a set of paramagnetic atoms. In the latter
case it is well known that the atomic edm differs greatly from the electron edm
when the internal electric fields of the atom are taken into account. In the
nonrelativistic limit these fields lead to a complete suppression, but for
heavy atoms large enhancement factors are present. A general bound-state field
theory approach applicable to both the neutron and paramagnetic atoms is set
up. It is applied first to the neutron, treating the quarks as moving freely in
a confining spherical well. It is shown that the effect of internal electric
fields is small in this case. The atomic problem is then revisited using
field-theory techniques in place of the usual Hamiltonian methods, and the
atomic enhancement factor is shown to be consistent with previous calculations.
Possible application of bound-state techniques to other sources of the neutron
edm is discussed.Comment: 21 pages, 5 figure
An analytical treatment of in-plane magnetotransport in the Falicov-Sievert model
We derive an analytical expression which allows efficient computation of the
effect of all the Fermi surface trajectories induced by a combination of Bragg
scattering and magnetic breakdown on the in-plane components of the resistivity
tensor. The particular network of coupled orbits which we consider was first
formulated by Falicov and Sievert, who studied the problem numerically. Our
approach, based upon a method used previously to derive an analytical solution
for interlayer transport, allows us to show that the conductivity tensor can be
written as a sum of a matrix representing the effect of total magnetic
breakdown and one representing a combination of complex electronic
trajectories, and we find a compact expression for the in-plane components of
the resistivity tensor that can be evaluated straightforwardly.Comment: 4 pages, 4 figure
Thermodynamic and magnetic properties of the layered triangular magnet NaNiO2
We report muon-spin rotation, heat capacity, magnetization, and ac magnetic
susceptibility measurements of the layered spin-1/2 antiferromagnet NaNiO2.
These show the onset of long-range magnetic order below T_N = 19.5K. Rapid muon
depolarization persisting to about 5K above T_N is consistent with the presence
of short-range magnetic order. The temperature and frequency dependence of the
ac susceptibility suggests that magnetic clusters persist above 25K in the
paramagnetic state and that their volume fraction decreases with increasing
temperature. A frequency dependent peak in the ac magnetic susceptibility at
T_sf = 3K is observed, consistent with a slowing of spin fluctuations at this
temperature. A partial magnetic phase diagram is deduced.Comment: 4 pages, 4 figure
Recommended from our members
With flying colours: pilot performance with colour-coded head-up flight symbology
The manipulation of colour in display symbology design has long been recognised as a method to improve operator experience and performance. Recent developments in colour head-up display (HUD) and helmet-mounted display (HMD) technology underline the necessity to understand the human factors considerations of symbology colour coding against conventional monochrome symbology formats. In this low-fidelity desktop human-in-the-loop experiment, the colour of flight symbology on an overlaid symbology set was coded as a redundant cue to indicate the accuracy of professional and non-professional pilots’ flight profile across a range of simulated flight manoeuvres. The main finding of this study was that colour coding flight symbology supported the manual flying performance of both professional and non-professional pilots. Notably, colour-coding of the bank indicator and airspeed tape minimised performance error during turning and altitude change manoeuvres, respectively. The usability of colour coded symbology was also rated higher than the monochrome symbology. We conclude that colour coded HUD/HMD symbology is preferred by the user and may improve performance during low workload manual flying tasks. A fuller understanding of performance and workload effects will require future studies to employ higher workload flying tasks and examine the utility of colour coding within higher fidelity environments
Determination of characteristic muon precession and relaxation signals in FeAs and FeAs2, possible impurity phases in pnictide superconductors
We report muon-spin relaxation measurements of highly homogeneous samples of
FeAs and FeAs2, both previously found as impurity phases in some samples of
recently synthesized pnictide superconductors. We observe well defined muon
precession in the FeAs sample with two precession frequencies of 38.2(3) and
22.7(9) MHz at 7.5 K, with the majority of the amplitude corresponding to the
lower frequency component. In FeAs2 we confirm previous measurements showing
that no long-ranged magnetic order occurs above 2 K and measure the muon spin
relaxation rate, which increases on cooling. Our results exclude the
possibility that previous muon-spin relaxation measurements of pnictide
superconductors have been measuring the effect of these possible impurities.Comment: 4 pages, 3 figures, corrected Figure
The inverse-Compton ghost HDF 130 and the giant radio galaxy 6C 0905+3955: matching an analytic model for double radio source evolution
We present new GMRT observations of HDF 130, an inverse-Compton (IC) ghost of
a giant radio source that is no longer being powered by jets. We compare the
properties of HDF 130 with the new and important constraint of the upper limit
of the radio flux density at 240 MHz to an analytic model. We learn what values
of physical parameters in the model for the dynamics and evolution of the radio
luminosity and X-ray luminosity (due to IC scattering of the cosmic microwave
background (CMB)) of a Fanaroff-Riley II (FR II) source are able to describe a
source with features (lobe length, axial ratio, X-ray luminosity, photon index
and upper limit of radio luminosity) similar to the observations. HDF 130 is
found to agree with the interpretation that it is an IC ghost of a powerful
double-lobed radio source, and we are observing it at least a few Myr after jet
activity (which lasted 5--100 Myr) has ceased. The minimum Lorentz factor of
injected particles into the lobes from the hotspot is preferred to be
for the model to describe the observed quantities well,
assuming that the magnetic energy density, electron energy density, and lobe
pressure at time of injection into the lobe are linked by constant factors
according to a minimum energy argument, so that the minimum Lorentz factor is
constrained by the lobe pressure. We also apply the model to match the features
of 6C 0905+3955, a classical double FR II galaxy thought to have a low-energy
cutoff of in the hotspot due to a lack of hotspot
inverse-Compton X-ray emission. The models suggest that the low-energy cutoff
in the hotspots of 6C 0905+3955 is , just slightly above
the particles required for X-ray emission.Comment: 9 pages, 3 figure
Measurements of thermodynamic and transport properties of EuC: a low-temperature analogue of EuO
EuC is a ferromagnet with a Curie-temperature of K. It
is semiconducting with the particularity that the resistivity drops by about 5
orders of magnitude on cooling through , which is therefore called a
metal-insulator transition. In this paper we study the magnetization, specific
heat, thermal expansion, and the resistivity around this ferromagnetic
transition on high-quality EuC samples. At we observe well defined
anomalies in the specific heat and thermal expansion data.
The magnetic contributions of and can satisfactorily be
described within a mean-field theory, taking into account the magnetization
data. In zero magnetic field the magnetic contributions of the specific heat
and thermal expansion fulfill a Gr\"uneisen-scaling, which is not preserved in
finite fields. From an estimation of the pressure dependence of via
Ehrenfest's relation, we expect a considerable increase of under applied
pressure due to a strong spin-lattice coupling. Furthermore the influence of
weak off stoichiometries in EuC was studied. It is
found that strongly affects the resistivity, but hardly changes the
transition temperature. In all these aspects, the behavior of EuC strongly
resembles that of EuO.Comment: 7 pages, 6 figure
- …