1,437 research outputs found
The Z=82 shell closure in neutron-deficient Pb isotopes
Recent mass measurements show a substantial weakening of the binding energy
difference delta_{2p} (Z,N) = E(Z-2,N) - 2 E(Z,N) + E(Z+2,N) in the
neutron-deficient Pb isotopes. As delta_{2p} is often attributed to the size of
the proton magic gap, it might be speculated that the reduction in delta_{2p}
is related to a weakening of the spherical Z=82 shell. We demonstrate that the
observed trend is described quantitatively by self-consistent mean-field models
in terms of deformed ground states of Hg and Po isotopes.Comment: submitted to Eur. Phys. J.
Heat capacity studies of Ce and Rh site substitution in the heavy fermion antiferromagnet CeRhIn_5;: Short-range magnetic interactions and non-Fermi-liquid behavior
In heavy fermion materials superconductivity tends to appear when long range
magnetic order is suppressed by chemical doping or applying pressure. Here we
report heat capacity measurements on diluted alloyes of the heavy fermion
superconductor CeRhIn_5;. Heat capacity measurements have been performed on
CeRh_{1-y}Ir_{y}In_5; (y <= 0.10) and Ce_{1-x}La_{x}Rh_{1-y}Ir_{y}In_5; (x <=
0.50) in applied fields up to 90 kOe to study the affect of doping and magnetic
field on the magnetic ground state. The magnetic phase diagram of
CeRh_{0.9}Ir_{0.1}In_5; is consistent with the magnetic structure of CeRhIn_5;
being unchanged by Ir doping. Doping of Ir in small concentrations is shown to
slightly increase the antiferromagnetic transition temperature T_{N} (T_{N}=3.8
K in the undoped sample). La doping which causes disorder on the Ce sublattice
is shown to lower T_{N} with no long range order observed above 0.34 K for
Ce_{0.50}La_{0.50}RhIn_5;. Measurements on Ce_{0.50}La_{0.50}RhIn_5; show a
coexistence of short range magnetic order and non-Fermi-liquid behavior. This
dual nature of the Ce 4f-electrons is very similar to the observed results on
CeRhIn_5; when long range magnetic order is suppressed at high pressure.Comment: 8 pages, 9 figure
Localized f electrons in CexLa1-xRhIn5: dHvA Measurements
Measurements of the de Haas-van Alphen effect in CexLa1-xRhIn5 reveal that
the Ce 4f electrons remain localized for all x, with the mass enhancement and
progressive loss of one spin from the de Haas-van Alphen signal resulting from
spin fluctuation effects. This behavior may be typical of antiferromagnetic
heavy fermion compounds, inspite of the fact that the 4f electron localization
in CeRhIn5 is driven, in part, by a spin-density wave instability.Comment: 4 pages, 4 figures, submitted to PR
Three-dimensional diffraction mapping by tuning the X-ray energy
Three-dimensional reciprocal-space maps of a single SiGe island around the Si(004) Bragg peak are recorded using an energy-tuning technique with a microfocused X-ray beam with compound refractive lenses as focusing optics
Compressibility of and (M = Rh, Ir and Co) Compounds
The lattice parameters of the tetragonal compounds CeIn and
CeIn(Rh, Ir and Co) have been studied as a function of
pressure up to 15 GPa using a diamond anvil cell under both hydrostatic and
quasihydrostatic conditions at room temperature. The addition of In
layers to the parent CeIn compound is found to stiffen the lattice as the
2-layer systems (average of bulk modulus values is 70.4 GPa) have a
larger than CeIn (67 GPa), while the 1-layer systems with the are
even stiffer (average of is 81.4 GPa). Estimating the hybridization
using parameters from tight binding calculations shows that the dominant
hybridization is in nature between the Ce and In atoms. The values of
at the pressure where the superconducting transition temperature
reaches a maximum is the same for all CeIn compounds. By
plotting the maximum values of the superconducting transition temperature
versus for the studied compounds and Pu-based superconductors, we
find a universal versus behavior when these quantities are
normalized appropriately. These results are consistent with magnetically
mediated superconductivity.Comment: Updated version resubmitted to Phys. Rev.
Absence of Hybridization Gap in Heavy Electron Systems and Analysis of YbAl3 in terms of Nearly Free Electron Conduction Band
In the analysis of the heavy electron systems, theoretical models with c-f
hybridization gap are often used. We point out that such a gap does not exist
and the simple picture with the hybridization gap is misleading in the metallic
systems, and present a correct picture by explicitly constructing an effective
band model of YbAl_3. Hamiltonian consists of a nearly free electron model for
conduction bands which hybridize with localized f-electrons, and includes only
a few parameters. Density of states, Sommerfeld coefficient, f-electron number
and optical conductivity are calculated and compared with the band calculations
and the experiments.Comment: 9 pages, 9 figures, submitted to J. Phys. Soc. Jp
Unusual giant magnetostriction in the ferrimagnet GdCaMnO
We report an unusual giant linear magnetostrictive effect in the ferrimagnet
GdCaMnO (80 K). Remarkably, the
magnetostriction, negative at high temperature (), becomes
positive below 15 K when the magnetization of the Gd sublattice overcomes the
magnetization of the Mn sublattice. A rather simple model where the magnetic
energy competes against the elastic energy gives a good account of the observed
results and confirms that Gd plays a crucial role in this unusual observation.
Unlike previous works in manganites where only striction associated with 3
Mn orbitals is considered, our results show that the lanthanide 4 orbitals
related striction can be very important too and it cannot be disregarded.Comment: 6 pages, 3 figure
Prevalence of plant-parasitic nematodes associated with tomatoes in three agro-ecological zones of Ghana
A study was conducted between August 2014 and May 2015 to identify plant-parasitic nematodes taxa associated with tomato (Solanum lycopersicum L.) and to assess the knowledge, perceptions and experiences of growers of the crop on occurrence and management of the parasites on their farms in nine communities within the semi-deciduous forest, the forest/savanna transitional and the savanna agro-ecological zones of Ghana. Semi-structured questionnaires were designed and administered to 54 randomly selected growers from the nine communities. Composite rhizosphere soil and tomato root samples were collected from two farms in each of the nine communities, and nematodes extracted, identified and recorded. The study revealed that many growers (73%) could not distinguish between nematode infestation, nutrient deficiency and moisture stress and, therefore, lacked knowledge on nematode control. Most of the growers (63%) continually cropped their land to tomato for periods of 4 –7 years without fallowing. All growers applied only inorganic fertilizer to their crops. Symptoms of nematode infestation were widespread in fields with high yield losses. Tomato was a host to Helicotylenchus spp. (11.5% in soil), Hoplolaimus spp. (1.0 % in soil), Meloidogyne spp. (37.4% in soil and 69.3% in roots), Pratylenchus spp. (20.6% in soil and 13.7% in roots), Rotylenchulus spp. (11.0% in soil and 12.2% in roots), Scutellonema spp. (9.5% in soil and 4.9% in roots), Tylenchus spp.(7.6% in soil) and Xiphinema spp.(1.4% in soil) across the nine communities surveyed. Semi-deciduous forest and Savanna agro-ecological zones had the highest and least population densities of nematodes, respectively. These nematodes, if not managed efficiently, could also serve as constraint to tomato production in the country
Magnetic-Field-Induced Antiferromagnetism in Two-Dimensional Hubbard Model: Analysis of CeRhIn
We propose the mechanism for the magnetic-field-induced antiferromagnetic
(AFM) state in a two-dimensional Hubbard model in the vicinity of the AFM
quantum critical point (QCP), using the fluctuation-exchange (FLEX)
approximation by taking the Zeeman energy due to the magnetic field into
account. In the vicinity of the QCP, we find that the AFM correlation
perpendicular to is enhanced, whereas that parallel to is reduced. This
fact means that the finite magnetic field increases , with the AFM order
perpendicular to . The increment in can be understood in terms of the
reduction of both quantum and thermal fluctuations due to the magnetic field,
which is caused by the self-energy effect within the FLEX approximation. The
present study naturally explains the increment in in CeRhIn_5 under the
magnetic field found recently.Comment: 5 page
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