257 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
Is there a unique thermal source of dileptons in Pb(158 AGeV) + Au, Pb reactions?
An analysis of the dilepton measurements in the reactions Pb(158 AGeV)
+ Au, Pb points to a unique thermal source contributing to the invariant mass
and transverse momentum spectra. Effects of the flow pattern are discussed.Comment: 7 LaTeX pages including eps figure
Coexistence of Magnetic Order and Two-dimensional Superconductivity at LaAlO/SrTiO Interfaces
A two dimensional electronic system with novel electronic properties forms at
the interface between the insulators LaAlO and SrTiO. Samples
fabricated until now have been found to be either magnetic or superconducting,
depending on growth conditions. We combine transport measurements with
high-resolution magnetic torque magnetometry and report here evidence of
magnetic ordering of the two-dimensional electron liquid at the interface. The
magnetic ordering exists from well below the superconducting transition to up
to 200 K, and is characterized by an in-plane magnetic moment. Our results
suggest that there is either phase separation or coexistence between magnetic
and superconducting states. The coexistence scenario would point to an
unconventional superconducting phase in the ground state.Comment: 10 pages, 4 figure
The properties of V838 Mon in 2002 November
We present the results of modelling the 0.45--1 micron spectral energy
distribution of V838 Mon for 2002 November. Synthetic spectra were calculated
using the NextGen model atmospheres of Hauschildt et al. (1999), which
incorporate line lists for H2O, TiO, CrH, FeH, CO, and MgH, as well as the VALD
atomic line list. Fits to the observed spectra show that, in 2002 November, the
effective temperature of V838 Mon was approximately 2000 +/-100 K. Our
theoretical spectra show a comparatively weak dependence on log g. Preliminary
analysis of the hot star observed together with V838 Mon shows it to be a
normal B3V dwarf.Comment: 7 pages, 4 figs, accepted by A&
Vlasov-Maxwell, self-consistent electromagnetic wave emission simulations in the solar corona
1.5D Vlasov-Maxwell simulations are employed to model electromagnetic
emission generation in a fully self-consistent plasma kinetic model for the
first time in the solar physics context. The simulations mimic the plasma
emission mechanism and Larmor drift instability in a plasma thread that
connects the Sun to Earth with the spatial scales compressed appropriately. The
effects of spatial density gradients on the generation of electromagnetic
radiation are investigated. It is shown that 1.5D inhomogeneous plasma with a
uniform background magnetic field directed transverse to the density gradient
is aperiodically unstable to Larmor-drift instability. The latter results in a
novel effect of generation of electromagnetic emission at plasma frequency.
When density gradient is removed (i.e. when plasma becomes stable to
Larmor-drift instability) and a density, super-thermal, hot beam is
injected along the domain, in the direction perpendicular to the magnetic
field, plasma emission mechanism generates non-escaping Langmuir type
oscillations which in turn generate escaping electromagnetic radiation. It is
found that in the spatial location where the beam is injected, the standing
waves, oscillating at the plasma frequency, are excited. These can be used to
interpret the horizontal strips observed in some dynamical spectra. Quasilinear
theory predictions: (i) the electron free streaming and (ii) the beam long
relaxation time, in accord with the analytic expressions, are corroborated via
direct, fully-kinetic simulation. Finally, the interplay of Larmor-drift
instability and plasma emission mechanism is studied by considering
electron beam in the Larmor-drift unstable (inhomogeneous) plasma.
http://www.maths.qmul.ac.uk/~tsiklauri/movie1.mpg *
http://www.maths.qmul.ac.uk/~tsiklauri/movie2.mpg *
http://www.maths.qmul.ac.uk/~tsiklauri/movie3.mpgComment: Solar Physics (in press, the final, accepted version
Exact results with the Kotliar-Ruckenstein slave-boson representation
Radial slave boson representations have the particular advantage that the
expectation values of their respective fields are finite even without the
formal introduction of spurious Bose condensates for each of the bosonic
fields. The expectation values of the radial (real) fields are in fact to be
interpreted as the density of empty or singly occupied sites. Whereas the
radial representation of the Barnes slave bosons has been investigated before,
a setup for the functional integral of radial bosonic fields in the more
physical Kotliar-Ruckenstein representation has not been accomplished to date.
We implement a path integral procedure with suitable renormalization factors
for a strongly correlated two-site model which allows to control the formal
steps in the intricate evaluation, as the results for the partition function
and the expectation values are known from exact diagonalization for such a
minimal single impurity Anderson model. The partition function is shown to be a
trace over a product of matrices local in time and therefore can be calculated
analytically. Eventually, we establish the scheme for the evaluation of
correlation functions and thermodynamic properties.Comment: 10 pages, 1 figur
Oxide Heterostructures from a Realistic Many-Body Perspective
Oxide heterostructures are a new class of materials by design, that open the
possibility for engineering challenging electronic properties, in particular
correlation effects beyond an effective single-particle description. This short
review tries to highlight some of the demanding aspects and questions,
motivated by the goal to describe the encountered physics from first
principles. The state-of-the-art methodology to approach realistic many-body
effects in strongly correlated oxides, the combination of density functional
theory with dynamical mean-field theory, will be briefly introduced. Discussed
examples deal with prominent Mott-band- and band-band-insulating type of oxide
heterostructures, where different electronic characteristics may be stabilized
within a single architectured oxide material.Comment: 19 pages, 9 figure
The rovibrational spectrum of BeH, MgH and CaH at high temperatures in the state: a theoretical study
Accurate line lists for three molecules, BeH, MgH and CaH, in their ground
electronic states are presented. These line lists are suitable for temperatures
relevant to exoplanetary atmospheres and cool stars (up to 2000K). A
combination of empirical and \textit{ab initio} methods is used. The
rovibrational energy levels of BeH, MgH and CaH are computed using the programs
Level and DPotFit in conjunction with `spectroscopic' potential energy curves
(PECs). The PEC of BeH is taken from the literature, while the PECs of CaH and
MgH are generated by fitting to the experimental transition energy levels. Both
spin-rotation interactions (except for BeH, for which it is negligible) and
non-adiabatic corrections are explicitly taken into account. Accurate line
intensities are generated using newly computed \textit{ab initio} dipole moment
curves for each molecule using high levels of theory. Full line lists of
rotation-vibration transitions for BeH, MgH, MgH, MgH
and CaH are made available in an electronic form as supplementary data
to this article and at \url{www.exomol.com}.Comment: MNRAS (in press
Thermal Dileptons at LHC
We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb
collisions at LHC. Hadronic emission in the low-mass region is calculated using
in-medium spectral functions of light vector mesons within hadronic many-body
theory. In the intermediate-mass region thermal radiation from the Quark-Gluon
Plasma, evaluated perturbatively with hard-thermal loop corrections, takes
over. An important source over the entire mass range are decays of correlated
open-charm hadrons, rendering the nuclear modification of charm and bottom
spectra a critical ingredient.Comment: 2 pages, 2 figures, contributed to Workshop on Heavy Ion Collisions
at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun
2007 v2: acknowledgment include
A Universal Critical Density Underlying the Physics of Electrons at the LaAlO3/SrTiO3 Interface
The two-dimensional electron system formed at the interface between the
insulating oxides LaAlO3 and SrTiO3 exhibits ferromagnetism, superconductivity,
and a wide range of unique magnetotransport properties. A key challenge is to
find a unified microscopic mechanism that underlies these emergent phenomena.
Here we show that a universal Lifshitz transition between d-orbitals lies at
the core of the observed transport phenomena in this system. Our measurements
find a critical electronic density at which the transport switches from single
to multiple carriers. This density has a universal value, independent of the
LaAlO3 thickness and electron mobility. The characteristics of the transition,
its universality, and its compatibility with spectroscopic measurements
establish it as a transition between d-orbitals of different symmetries. A
simple band model, allowing for spin-orbit coupling at the atomic level,
connects the observed universal transition to a range of reported
magnetotransport properties. Interestingly, we also find that the maximum of
the superconducting transition temperature occurs at the same critical
transition, indicating a possible connection between the two phenomena. Our
observations demonstrate that orbital degeneracies play an important role in
the fascinating behavior observed so far in these oxides
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