9,411 research outputs found
Heavy fermion behavior of itinerant frustrated systems: beta-Mn, Y(Sc)Mn_{2} and LiV_{2}O_{4}$
These three metallic systems do not exhibit any magnetic ordering despite
experiments show the existence of localized moments with large
antiferromagnetic exchange: this is a consequence of the strong geometric
frustration (Y(Sc)Mn_{2} and LiV_{2}O_{4} have the Pyrochlore structure, while
beta-Mn has a more complicated frustrated structure). Another common feature is
their very large specific heat coefficient \gamma =C/T (420 mJ mole^{-1} K^{-2}
for LiV_{2}O_{4}). Several explanations have been proposed for this ''3d heavy
fermion behavior'', including a 3d-Kondo effect. However the similarities
between the three compounds indicate that frustration plays a big role. We
propose a new model which takes into account the existence of two types of
3d-electrons (localized and itinerant) and a frustrated antiferromagnetic
exchange between the localized 3d electrons.Comment: Proceedings of HFM-Conference, June 2000, Waterloo, Ontario, Canada
To appear in Can. J. Phy
A Lee-Yang--inspired functional with a density--dependent neutron-neutron scattering length
Inspired by the low--density Lee-Yang expansion for the energy of a dilute
Fermi gas of density and momentum , we introduce here a
Skyrme--type functional that contains only -wave terms and provides, at the
mean--field level, (i) a satisfactory equation of state for neutron matter from
extremely low densities up to densities close to the equilibrium point, and
(ii) a good--quality equation of state for symmetric matter at density scales
around the saturation point. This is achieved by using a density--dependent
neutron-neutron scattering length ) which satisfies the low--density
limit (for Fermi momenta going to zero) and has a density dependence tuned in
such a way that the low--density constraint is satisfied
at all density scales.Comment: 5 figure
From dilute matter to the equilibrium point in the energy--density--functional theory
Due to the large value of the scattering length in nuclear systems, standard
density--functional theories based on effective interactions usually fail to
reproduce the nuclear Fermi liquid behavior both at very low densities and
close to equilibrium. Guided on one side by the success of the Skyrme density
functional and, on the other side, by resummation techniques used in Effective
Field Theories for systems with large scattering lengths, a new energy--density
functional is proposed. This functional, adjusted on microscopic calculations,
reproduces the nuclear equations of state of neutron and symmetric matter at
various densities. Furthermore, it provides reasonable saturation properties as
well as an appropriate density dependence for the symmetry energy.Comment: 4 figures, 2 table
Voltage induced control and magnetoresistance of noncollinear frustrated magnets
Noncollinear frustrated magnets are proposed as a new class of spintronic
materials with high magnetoresistance which can be controlled with relatively
small applied voltages. It is demonstrated that their magnetic configuration
strongly depends on position of the Fermi energy and applied voltage. The
voltage induced control of noncollinear frustrated materials (VCFM) can be seen
as a way to intrinsic control of colossal magnetoresistance (CMR) and is the
bulk material counterpart of spin transfer torque concept used to control giant
magnetoresistance in layered spin-valve structures.Comment: 4 pages, 4 figure
Ultrafast dynamics of finite Hubbard clusters - a stochastic mean-field approach
Finite lattice models are a prototype for strongly correlated quantum systems
and capture essential properties of condensed matter systems. With the dramatic
progress in ultracold atoms in optical lattices, finite fermionic Hubbard
systems have become directly accessible in experiments, including their
ultrafast dynamics far from equilibrium. Here, we present a theoretical
approach that is able to treat these dynamics in any dimension and fully
includes inhomogeneity effects. The method consists in stochastic sampling of
mean-field trajectories and is found to be more accurate and efficient than
current nonequilibrium Green functions approaches. This is demonstrated for
Hubbard clusters with up to 512 particles in one, two and three dimensions
From bare interactions, low--energy constants and unitary gas to nuclear density functionals without free parameters: application to neutron matter
We further progress along the line of Ref. [Phys. Rev. {\bf A 94}, 043614
(2016)] where a functional for Fermi systems with anomalously large -wave
scattering length was proposed that has no free parameters. The
functional is designed to correctly reproduce the unitary limit in Fermi gases
together with the leading-order contributions in the s- and p-wave channels at
low density. The functional is shown to be predictive up to densities
fm that is much higher densities compared to the Lee-Yang
functional, valid for fm. The form of the functional
retained in this work is further motivated. It is shown that the new functional
corresponds to an expansion of the energy in and to all
orders, where is the effective range and is the Fermi momentum. One
conclusion from the present work is that, except in the extremely low--density
regime, nuclear systems can be treated perturbatively in with
respect to the unitary limit. Starting from the functional, we introduce
density--dependent scales and show that scales associated to the bare
interaction are strongly renormalized by medium effects. As a consequence, some
of the scales at play around saturation are dominated by the unitary gas
properties and not directly to low-energy constants. For instance, we show that
the scale in the s-wave channel around saturation is proportional to the
so-called Bertsch parameter and becomes independent of . We also
point out that these scales are of the same order of magnitude than those
empirically obtained in the Skyrme energy density functional. We finally
propose a slight modification of the functional such that it becomes accurate
up to the saturation density fm
Superfluid fission dynamics with microscopic approaches
Recent progresses in the description of the latter stage of nuclear fission
are reported. Dynamical effects during the descent of the potential towards
scission and in the formation of the fission fragments are studied with the
time-dependent Hartree-Fock approach with dynamical pairing correlations at the
BCS level. In particular, this approach is used to compute the final kinetic
energy of the fission fragments. Comparison with experimental data on the
fission of 258Fm are made.Comment: Proceeding of the "International Conference on Nuclear Structure and
Related Topics" (NSRT15
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