891 research outputs found
Magnetically ordered state at correlated oxide interfaces: the role of random oxygen defects
Using an effective one-band Hubbard model with disorder, we consider magnetic
states of the correlated oxide interfaces, where effective hole self-doping and
a magnetially ordered state emerge due to electronic and ionic reconstructions.
By employing the coherent potential approximation, we analyze the effect of
random oxygen vacancies on the two-dimensional magnetism. We find that the
random vacancies enhance the ferromagnetically ordered state and stabilize a
robust magnetization above a critical vacancy concentration of about c=0.1. In
the strong-correlated regime, we also obtain a nonmonotonic increase of the
magnetization upon an increase of vacancy concentration and a substantial
increase of the magnetic moments, which can be realized at oxygen reduced
high-Tc cuprate interfaces.Comment: 8 pages, 2 figures, submitted to J Supercond Novel Magnetism (ICSM12
conference contribution
A search for lithium in metal-poor L dwarfs
The aim of the project is to search for lithium in absorption at 6707.8
Angstroms to constrain the nature and the mass of the brightest low-metallicity
L-type dwarfs (refered to as L subdwarfs) identified in large-scale surveys.
We obtained low- to intermediate-resolution (R~2500-9000) optical (~560-770
nm) spectra of two mid-L subdwarfs, SDSSJ125637.13-022452.4 (SDSS1256; sdL3.5)
and 2MASSJ162620.14+392519.5 (2MASS1626; sdL4) with spectrographs on the
European Southern Observatory Very Large Telescope and the Gran Telescopio de
Canarias.
We report the presence of a feature at the nominal position of the lithium
absorption doublet at 6707.8 Angstroms in the spectrum of SDSS1256, with an
equivalent width of 66+/-27 Angstroms at 2.4 sigma, which we identify as
arising from a CaH molecular transition based on atmosphere models. We do not
see any feature at the position of the lithium feature in the spectrum of
2MASS1626. The existence of overlapping molecular absorption sets a confusion
detection limit of [Li/H]=-3 for equivalently-typed L subdwarfs. We provided
improved radial velocity measurements of -126+/-10 km/s and -239+/-12 km/s for
SDSS1256 and 2MASS1626, respectively, as well as revised Galactic orbits. We
implemented adjusting factors for the CaH molecule in combination with the
NextGen atmosphere models to fit the optical spectrum of SDSS1256 in the
6200-7300 Angstroms range. We also estimate the expected Li abundance from
interstellar accretion ([Li/H]=-5), place limits on circumstellar accretion
(10^9 g/yr), and discuss the prospects of Li searches in cooler L and T
subdwarfs.Comment: 9 pages, 6 figures, 4 tables, accepted to A&
Jet-induced gauge field instabilities in the quark-gluon plasma: A kinetic theory approach
We discuss the properties of the collective modes of a system composed by a
thermalized quark-gluon plasma traversed by a relativistic jet of partons. The
transport equations obeyed by the components of the plasma and of the jet are
studied in the Vlasov approximation. Assuming that the partons in the jet can
be described with a tsunami-like distribution function we derive the
expressions of the dispersion law of the collective modes. Then the behavior of
the unstable gauge modes of the system is analyzed for various values of the
velocity of the jet, of the momentum of the collective modes and of the angle
between these two quantities. We find that the most unstable modes are those
with momentum orthogonal to the velocity of the jet and that these
instabilities appear when the velocity of the jet is higher than a threshold
value, which depends on the plasma and jet frequencies. The results obtained
within the Vlasov approximation are compared with the corresponding results
obtained using a chromohydrodynamical approach.The effect we discuss here
suggests a possible collective mechanism for the description of the jet
quenching phenomena in heavy ion collisions.Comment: 13 pages, 6 figure
Interface hole-doping in cuprate-titanate superlattices
The electronic structure of interfaces between YBaCuO and
SrTiO is studied using local spin density approximation (LSDA) with
intra-atomic Coulomb repulsion (LSDA+U). We find a metallic state in
cuprate/titanate heterostructures with the hole carriers concentrated
substantially in the CuO-layers and in the first interface TiO and SrO
planes. This effective interface doping appears due to the polarity of
interfaces, caused by the first incomplete copper oxide unit cell.
Interface-induced high pre-doping of CuO-layers is a key mechanism
controlling the superconducting properties in engineered field-effect devices
realized on the basis of cuprate/titanate superlattices.Comment: 5 pages, 5 figure
Oxygen vacancies at titanate interfaces: two-dimensional magnetism and orbital reconstruction
We show that oxygen vacancies at titanate interfaces induce a complex
multiorbital reconstruction which involves a lowering of the local symmetry and
an inversion of t2g and eg orbitals resulting in the occupation of the eg
orbitals of Ti atoms neighboring the O vacancy. The orbital reconstruction
depends strongly on the clustering of O vacancies and can be accompanied by a
magnetic splitting between the local eg orbitals with lobes directed towards
the vacancy and interface dxy orbitals. The reconstruction generates a
two-dimensional interface magnetic state not observed in bulk SrTiO3. Using
generalized gradient approximation (LSDA) with intra-atomic Coulomb repulsion
(GGA+U), we find that this magnetic state is common for titanate surfaces and
interfaces.Comment: 13 pages, 18 figures, to appear in Physical Review
Electronic charge and orbital reconstruction at cuprate-titanate interfaces
In complex transition metal oxide heterostructures of physically dissimilar
perovskite compounds, interface phenomena can lead to novel physical properties
not observed in either of their constituents. This remarkable feature opens new
prospects for technological applications in oxide electronic devices based on
nm-thin oxide films. Here we report on a significant electronic charge and
orbital reconstruction at interfaces between YBa2Cu3O6 and SrTiO3 studied using
local spin density approximation (LSDA) with intra-atomic Coulomb repulsion
(LSDA+U). We show that the interface polarity results in the metallicity of
cuprate-titanate superlattices with the hole carriers concentrated
predominantly in the CuO2 and BaO layers and in the first interface TiO2 and
SrO planes. We also find that the interface structural relaxation causes a
strong change of orbital occupation of Cu 3d orbitals in the CuO2 layers. The
concomitant change of Cu valency from +2 to +3 is related to the partial
occupation of the Cu orbitals at the interface with SrO planes
terminating SrTiO3. Interface-induced predoping and orbital reconstruction in
CuO2 layers are key mechanisms which control the superconducting properties of
field-effect devices developed on the basis of cuprate-titanate
heterostructures.Comment: 11 pages, 8 figures, to appear in the "Proceedings of Third Joint
HLRB and KONWIHR Result and Reviewing Workshop", Springer 200
Magnetism and superconductivity at LAO/STO-interfaces: the role of Ti 3d interface electrons
Ferromagnetism and superconductivity are in most cases adverse. However,
recent experiments reveal that they coexist at interfaces of LaAlO3 and SrTiO3.
We analyze the magnetic state within density functional theory and provide
evidence that magnetism is not an intrinsic property of the two-dimensional
electron liquid at the interface. We demonstrate that the robust ferromagnetic
state is induced by the oxygen vacancies in SrTiO3- or in the LaAlO3-layer.
This allows for the notion that areas with increased density of oxygen
vacancies produce ferromagnetic puddles and account for the previous
observation of a superparamagnetic behavior in the superconducting state.Comment: 5 pages, 4 figures, to appear in Physical Review B (Rapid
Communications
Ложка для людей с тремором рук
Болезнь Паркинсона вызвана прогрессирующим разрушением и гибелью нейронов, вырабатывающих нейромедиатор дофамин. Из-за этого нарушается регуляция движений и мышечного тонуса, что проявляется характерным тремором, общей скованностью и нарушением позы и движений. Для паркинсонизма характерен тремор, возникающий в покое. Авторы разработали ложку для людей с болезнью Паркинсона, позволяющую держать её содержимое в неподвижном состоянии при воздействие на нее тремором рук
- …