53,849 research outputs found
Bound hole states in a ferromagnetic (Ga,Mn)As environment
A numerical technique is developed to solve the Luttinger-Kohn equation for
impurity states directly in k-space and is applied to calculate bound hole wave
functions in a ferromagnetic (Ga,Mn)As host. The rich properties of the band
structure of an arbitrarily strained, ferromagnetic zinc-blende semiconductor
yields various features which have direct impact on the detailed shape of a
valence band hole bound to an active impurity. The role of strain is discussed
on the basis of explicit calculations of bound hole states.Comment: 9 pages, 10 figure
Magnetically induced Ferroelectricity in BiCuO
The tetragonal copper oxide BiCuO has an unusual crystal structure
with a three-dimensional network of well separated CuO plaquettes. This
material was recently predicted to host electronic excitations with an
unconventional spectrum and the spin structure of its magnetically ordered
state appearing at T 43 K remains controversial. Here we present the
results of detailed studies of specific heat, magnetic and dielectric
properties of BiCuO single crystals grown by the floating zone
technique, combined with the polarized neutron scattering and high-resolution
X-ray measurements. Our polarized neutron scattering data show Cu spins are
parallel to the plane. Below the onset of the long range antiferromagnetic
ordering we observe an electric polarization induced by an applied magnetic
field, which indicates inversion symmetry breaking by the ordered state of Cu
spins. For the magnetic field applied perpendicular to the tetragonal axis, the
spin-induced ferroelectricity is explained in terms of the linear
magnetoelectric effect that occurs in a metastable magnetic state. A relatively
small electric polarization induced by the field parallel to the tetragonal
axis may indicate a more complex magnetic ordering in BiCuO
Quantum turbulence and correlations in Bose-Einstein condensate collisions
We investigate numerically simulated collisions between experimentally
realistic Bose-Einstein condensate wavepackets, within a regime where highly
populated scattering haloes are formed. The theoretical basis for this work is
the truncated Wigner method, for which we present a detailed derivation, paying
particular attention to its validity regime for colliding condensates. This
paper is an extension of our previous Letter [A. A. Norrie, R. J. Ballagh, and
C. W. Gardiner, Phys. Rev. Lett. 94, 040401 (2005)] and we investigate both
single-trajectory solutions, which reveal the presence of quantum turbulence in
the scattering halo, and ensembles of trajectories, which we use to calculate
quantum-mechanical correlation functions of the field
On the electronic structure of the charge-ordered phase in epitaxial and polycrystalline La1-xCaxMnO3 (x = 0.55, 0.67) perovskite manganites
In this work the charge transport properties of charge ordered (CO)
La1-xCaxMnO3 (LCMO) (x= 0.55, 0.67) epitaxial thin films and polycrystals are
discussed following the recent controversy of localised electron states vs.
weakly or de- localised charge density wave (CDW) states in CO manganites. The
transport properties were investigated by current vs. voltage, direct current
resistivity vs. temperature, local activation energy vs. temperature,
magnetoresistance and admittance spectroscopy measurements, which all indicated
a localised electronic structure in the single CO phase. Delocalised charge
anomalies observed previously may be restricted to phase separated materials.Comment: Physical Review B, to be publishe
R-process nucleosynthesis calculations with complete nuclear physics input
The r-process constitutes one of the major challenges in nuclear
astrophysics. Its astrophysical site has not yet been identified but there is
observational evidence suggesting that at least two possible sites should
contribute to the solar system abundance of r-process elements and that the
r-process responsible for the production of elements heavier than Z=56 operates
quite robustly producing always the same relative abundances. From the
nuclear-physics point of view the r-process requires the knowledge of a large
number of reaction rates involving exotic nuclei. These include neutron capture
rates, beta-decays and fission rates, the latter for the heavier nuclei
produced in the r-process. We have developed for the first time a complete
database of reaction rates that in addition to neutron-capture rates and
beta-decay half-lives includes all possible reactions that can induce fission
(neutron-capture, beta-decay and spontaneous fission) and the corresponding
fission yields. In addition, we have implemented these reaction rates in a
fully implicit reaction network. We have performed r-process calculations for
the neutrino-driven wind scenario to explore whether or not fission can
contribute to provide a robust r-process pattern
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