32,813 research outputs found
Suppression of ferromagnetic ordering in doped manganites: Effects of the superexchange interaction
From a Monte Carlo study of the ferromagnetic Kondo lattice model for doped
manganites, including the antiferromagnetic superexchange interaction
(), we found that the ferromagnetic ordering was suppressed as
increased. The ferromagnetic transition temperature , as obtained from a
mean field fit to the calculated susceptibilities, was found to decrease
monotonically with increasing . Further, the suppression in
scales with the bandwidth narrowing induced by the antiferromagnetic
frustration originating from . From these results, we propose that the
change in the superexchange interaction strength between the electrons
of the Mn ions is one of the mechanisms responsible for the suppression in
observed in manganites of the type
(LaPr)CaMnO.Comment: 5 pages, 6 figures. To appear in PR
Making vortices in dipolar spinor condensates via rapid adiabatic passage
We propose to the create vortices in spin-1 condensates via magnetic
dipole-dipole interaction. Starting with a polarized condensate prepared under
large axial magnetic field, we show that by gradually inverting the field,
population transfer among different spin states can be realized in a controlled
manner. Under optimal condition, we generate a doubly quantized vortex state
containing nearly all atoms in the condensate. The resulting vortex state is a
direct manifestation of the dipole-dipole interaction and spin textures in
spinor condensates. We also point out that the whole process can be
qualitatively described by a simple rapid adiabatic passage model.Comment: 4 pages, 4 figure
Tunnelling Effect and Hawking Radiation from a Vaidya Black Hole
In this paper, we extend Parikh' work to the non-stationary black hole. As an
example of the non-stationary black hole, we study the tunnelling effect and
Hawking radiation from a Vaidya black hole whose Bondi mass is identical to its
mass parameter. We view Hawking radiation as a tunnelling process across the
event horizon and calculate the tunnelling probability. We find that the result
is different from Parikh's work because is the function of
Bondi mass m(v)
Pairwise dwarf galaxy formation and galaxy downsizing: some clues from extremely metal-poor Blue Compact Dwarf galaxies
Some of the extremely metal-poor Blue Compact Dwarf galaxies (XBCDs) in the
nearby universe form galaxy pairs with remarkably similar properties. This fact
points to an intriguing degree of synchronicity in the formation history of
these binary dwarf galaxies and raises the question as to whether some of them
form and co-evolve pairwise (or in loose galaxy groups), experiencing recurrent
mild interactions and minor tidally induced star formation episodes throughout
their evolution. We argue that this hypothesis offers a promising conceptual
framework for the exploration of the retarded previous evolution and recent
dominant formation phase of XBCDs.Comment: To appear in the proceedings of the JENAM 2010 Symposium "Dwarf
Galaxies: Keys to Galaxy Formation and Evolution" (Lisbon, 9-10 September
2010), P. Papaderos, S. Recchi, G. Hensler (eds.), Springer Verlag (2011), in
pres
Dynamical properties of dipolar Fermi gases
We investigate dynamical properties of a one-component Fermi gas with
dipole-dipole interaction between particles. Using a variational function based
on the Thomas-Fermi density distribution in phase space representation, the
total energy is described by a function of deformation parameters in both real
and momentum space. Various thermodynamic quantities of a uniform dipolar Fermi
gas are derived, and then instability of this system is discussed. For a
trapped dipolar Fermi gas, the collective oscillation frequencies are derived
with the energy-weighted sum rule method. The frequencies for the monopole and
quadrupole modes are calculated, and softening against collapse is shown as the
dipolar strength approaches the critical value. Finally, we investigate the
effects of the dipolar interaction on the expansion dynamics of the Fermi gas
and show how the dipolar effects manifest in an expanded cloud.Comment: 14 pages, 8 figures, submitted to New J. Phy
Quantum refrigerator driven by current noise
We proposed a scheme to implement a self-contained quantum refrigerator
system composed of three rf-SQUID qubits, or rather, flux-biased phase qubits.
The three qubits play the roles of the target, the refrigerator and the heat
engine respectively. We provide different effective temperatures for the three
qubits, by imposing external current noises of different strengths. The
differences of effective temperatures give rise to the flow of free energy and
that drives the refrigerator system to cool down the target. We also show that
the efficiency of the system approaches the Carnot efficiency.Comment: 5 pages, 1 figur
The Effects of Halo Assembly Bias on Self-Calibration in Galaxy Cluster Surveys
Self-calibration techniques for analyzing galaxy cluster counts utilize the
abundance and the clustering amplitude of dark matter halos. These properties
simultaneously constrain cosmological parameters and the cluster
observable-mass relation. It was recently discovered that the clustering
amplitude of halos depends not only on the halo mass, but also on various
secondary variables, such as the halo formation time and the concentration;
these dependences are collectively termed assembly bias. Applying modified
Fisher matrix formalism, we explore whether these secondary variables have a
significant impact on the study of dark energy properties using the
self-calibration technique in current (SDSS) and the near future (DES, SPT, and
LSST) cluster surveys. The impact of the secondary dependence is determined by
(1) the scatter in the observable-mass relation and (2) the correlation between
observable and secondary variables. We find that for optical surveys, the
secondary dependence does not significantly influence an SDSS-like survey;
however, it may affect a DES-like survey (given the high scatter currently
expected from optical clusters) and an LSST-like survey (even for low scatter
values and low correlations). For an SZ survey such as SPT, the impact of
secondary dependence is insignificant if the scatter is 20% or lower but can be
enhanced by the potential high scatter values introduced by a highly correlated
background. Accurate modeling of the assembly bias is necessary for cluster
self-calibration in the era of precision cosmology.Comment: 13 pages, 5 figures, replaced to match published versio
An alternative non-Markovianity measure by divisibility of dynamical map
Identifying non-Markovianity with non-divisibility, we propose a measure for
non-Markovinity of quantum process. Three examples are presented to illustrate
the non-Markovianity, measure for non-Markovianity is calculated and discussed.
Comparison with other measures of non-Markovianity is made. Our
non-Markovianity measure has the merit that no optimization procedure is
required and it is finite for any quantum process, which greatly enhances the
practical relevance of the proposed measure.Comment: 6 pages, 3 figue
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