593 research outputs found
Hard-core Yukawa model for two-dimensional charge stabilized colloids
The hyper-netted chain (HNC) and Percus-Yevick (PY) approximations are used
to study the phase diagram of a simple hard-core Yukawa model of
charge-stabilized colloidal particles in a two-dimensional system. We calculate
the static structure factor and the pair distribution function over a wide
range of parameters. Using the statics correlation functions we present an
estimate for the liquid-solid phase diagram for the wide range of the
parameters.Comment: 7 pages, 9figure
Tight-binding parameters and exchange integrals of Ba_2Cu_3O_4Cl_2
Band structure calculations for Ba_2Cu_3O_4Cl_2 within the local density
approximation (LDA) are presented. The investigated compound is similar to the
antiferromagnetic parent compounds of cuprate superconductors but contains
additional Cu_B atoms in the planes. Within the LDA, metallic behavior is found
with two bands crossing the Fermi surface (FS). These bands are built mainly
from Cu 3d_{x^2-y^2} and O 2p_{x,y} orbitals, and a corresponding tight-binding
(TB) model has been parameterized. All orbitals can be subdivided in two sets
corresponding to the A- and B-subsystems, respectively, the coupling between
which is found to be small. To describe the experimentally observed
antiferromagnetic insulating state, we propose an extended Hubbard model with
the derived TB parameters and local correlation terms characteristic for
cuprates. Using the derived parameter set we calculate the exchange integrals
for the Cu_3O_4 plane. The results are in quite reasonable agreement with the
experimental values for the isostructural compound Sr_2Cu_3O_4Cl_2.Comment: 5 pages (2 tables included), 4 ps-figure
Transport Properties, Thermodynamic Properties, and Electronic Structure of SrRuO3
SrRuO is a metallic ferromagnet. Its electrical resistivity is reported
for temperatures up to 1000K; its Hall coefficient for temperatures up to 300K;
its specific heat for temperatures up to 230K. The energy bands have been
calculated by self-consistent spin-density functional theory, which finds a
ferromagnetic ordered moment of 1.45 per Ru atom. The measured
linear specific heat coefficient is 30mJ/mole, which exceeds the
theoretical value by a factor of 3.7. A transport mean free path at room
temperature of is found. The resistivity increases nearly
linearly with temperature to 1000K in spite of such a short mean free path that
resistivity saturation would be expected. The Hall coefficient is small and
positive above the Curie temperature, and exhibits both a low-field and a
high-field anomalous behavior below the Curie temperature.Comment: 6 pages (latex) and 6 figures (postscript, uuencoded.) This paper
will appear in Phys. Rev. B, Feb. 15, 199
Relativistic predictions of spin observables for exclusive proton knockout reactions
Within the framework of the relativistic distorted wave impulse approximation
(DWIA), we investigate the sensitivity of complete sets of polarization
transfer observables for exclusive proton knockout from the 3s,
2d and 2d states in Pb, at an incident laboratory
kinetic energy of 202 MeV, and for coincident coplanar scattering angles
(, ), to different distorting optical potentials,
finite-range (FR) versus zero-range (ZR) approximations to the DWIA, as well as
medium-modified meson-nucleon coupling constants and meson masses. Results are
also compared to the nonrelativistic DWIA predictions based on the
Schr\"{o}dinger equation.Comment: Submitted for publication to Physicical Review C, 23 pages, 7 figure
Theory of asymmetric non-additive binary hard-sphere mixtures
We show that the formal procedure of integrating out the degrees of freedom
of the small spheres in a binary hard-sphere mixture works equally well for
non-additive as it does for additive mixtures. For highly asymmetric mixtures
(small size ratios) the resulting effective Hamiltonian of the one-component
fluid of big spheres, which consists of an infinite number of many-body
interactions, should be accurately approximated by truncating after the term
describing the effective pair interaction. Using a density functional treatment
developed originally for additive hard-sphere mixtures we determine the zero,
one, and two-body contribution to the effective Hamiltonian. We demonstrate
that even small degrees of positive or negative non-additivity have significant
effect on the shape of the depletion potential. The second virial coefficient
, corresponding to the effective pair interaction between two big spheres,
is found to be a sensitive measure of the effects of non-additivity. The
variation of with the density of the small spheres shows significantly
different behavior for additive, slightly positive and slightly negative
non-additive mixtures. We discuss the possible repercussions of these results
for the phase behavior of binary hard-sphere mixtures and suggest that
measurements of might provide a means of determining the degree of
non-additivity in real colloidal mixtures
Anomalous Spin Dynamics observed by High Frequency ESR in Honeycomb Lattice Antiferromagnet InCu2/3V1/3O3
High-frequency ESR results on the S=1/2 Heisenberg hexagonal antiferromagnet
InCu2/3V1/3O3 are reported. This compound appears to be a rare model substance
for the honeycomb lattice antiferromagnet with very weak interlayer couplings.
The high-temperature magnetic susceptibility can be interpreted by the S=1/2
honeycomb lattice antiferromagnet, and it shows a magnetic-order-like anomaly
at TN=38 K. Although, the resonance field of our high-frequency ESR shows the
typical behavior of the antiferromagnetic resonance, the linewidth of our
high-frequency ESR continues to increase below TN, while it tends to decrease
as the temperature in a conventional three-dimensional antiferromagnet
decreases. In general, a honeycomb lattice antiferromagnet is expected to show
a simple antiferromagnetic order similar to that of a square lattice
antiferromagnet theoretically because both antiferromagnets are bipartite
lattices. However, we suggest that the observed anomalous spin dynamics below
TN is the peculiar feature of the honeycomb lattice antiferromagnet that is not
observed in the square lattice antiferromagnet.Comment: 5 pages, 5 figure
Neutron Scattering study of Sr_2Cu_3O_4Cl_2
We report a neutron scattering study on the tetragonal compound
Sr_2Cu_3O_4Cl_2, which has two-dimensional (2D) interpenetrating Cu_I and
Cu_{II} subsystems, each forming a S=1/2 square lattice quantum Heisenberg
antiferromagnet (SLQHA). The mean-field ground state is degenerate, since the
inter-subsystem interactions are geometrically frustrated. Magnetic neutron
scattering experiments show that quantum fluctuations lift the degeneracy and
cause a 2D Ising ordering of the Cu_{II} subsystem. Due to quantum fluctuations
a dramatic increase of the Cu_I out-of-plane spin-wave gap is also observed.
The temperature dependence and the dispersion of the spin-wave energy are
quantitatively explained by spin-wave calculations which include quantum
fluctuations explicitly. The values for the nearest-neighbor superexchange
interactions between the Cu_I and Cu_{II} ions and between the Cu_{II} ions are
determined experimentally to be J_{I-II} = -10(2)meV and J_{II}= 10.5(5)meV,
respectively. Due to its small exchange interaction, J_{II}, the 2D dispersion
of the Cu_{II} SLQHA can be measured over the whole Brillouin zone with thermal
neutrons, and a novel dispersion at the zone boundary, predicted by theory, is
confirmed. The instantaneous magnetic correlation length of the Cu_{II} SLQHA
is obtained up to a very high temperature, T/J_{II}\approx 0.75. This result is
compared with several theoretical predictions as well as recent experiments on
the S=1/2 SLQHA.Comment: Figures and equations are rearrange
Interplay of dynamical and structure effects in the observables for 12C(p,2p) near 400 MeV with polarized and unpolarized beams
CITATION: Mecca, A. et al. 2019. Interplay of dynamical and structure effects in the observables for 12C(p,2p) near 400 MeV with polarized and unpolarized beams. Physics Letters B, 798. doi:10.1016/j.physletb.2019.134989The original publication is available at https://www.sciencedirect.com/journal/physics-letters-bWe investigate the interplay of reaction mechanism and structure effects in the calculated cross sections and polarization observables for the direct 12C(p, 2p)reaction near 400 MeV around the Quasi Free Scattering (QFS) kinematical condition. We do the first consistent comparison between the scattering observables obtained from solutions of three-body Faddeev/Alt-Grassberger-Sandhas (F/AGS) equations and from the Distorted-Wave Impulse Approximation (DWIA). We explore structure effects on the calculated observables, making use of one-nucleon spectroscopic overlaps obtained from the quantum Monte Carlo (QMC) many-body wave functions and using a Woods-Saxon parametrization with parameters adjusted to experimental (p, 2p) data. We show, for the first time, that the two reaction formalisms exhibit a distinct behavior depending upon the kinematic conditions. We also show that the agreement between the experimental data and the theoretical results depends on the reaction formalism, kinematical conditions and optical model parametrizations in addition to the spectroscopic factors (SFs). The agreement between the data and predictions using QMC wave functions diminishes prominently for transitions to excited states of 11B.https://www.sciencedirect.com/science/article/pii/S0370269319307117?via%3DihubPublisher’s versio
- …