4,045 research outputs found
Interaction-induced chiral p_x \pm i p_y superfluid order of bosons in an optical lattice
The study of superconductivity with unconventional order is complicated in
condensed matter systems by their extensive complexity. Optical lattices with
their exceptional precision and control allow one to emulate superfluidity
avoiding many of the complications of condensed matter. A promising approach to
realize unconventional superfluid order is to employ orbital degrees of freedom
in higher Bloch bands. In recent work, indications were found that bosons
condensed in the second band of an optical chequerboard lattice might exhibit
p_x \pm i p_y order. Here we present experiments, which provide strong evidence
for the emergence of p_x \pm i p_y order driven by the interaction in the local
p-orbitals. We compare our observations with a multi-band Hubbard model and
find excellent quantitative agreement
Solitonic spin-liquid state due to the violation of the Lifshitz condition in FeTe
A combination of phenomenological analysis and M\"ossbauer spectroscopy
experiments on the tetragonal FeTe system indicates that the magnetic
ordering transition in compounds with higher Fe-excess, 0.11, is
unconventional. Experimentally, a liquid-like magnetic precursor with
quasi-static spin-order is found from significantly broadened M\"ossbauer
spectra at temperatures above the antiferromagnetic transition. The
incommensurate spin-density wave (SDW) order in FeTe is described by a
magnetic free energy that violates the weak Lifshitz condition in the Landau
theory of second-order transitions. The presence of multiple Lifshitz
invariants provides the mechanism to create multidimensional, twisted, and
modulated solitonic phases.Comment: 5 pages, 2 figure
Finding Galaxy Groups In Photometric Redshift Space: the Probability Friends-of-Friends (pFoF) Algorithm
We present a structure finding algorithm designed to identify galaxy groups
in photometric redshift data sets: the probability friends-of-friends (pFoF)
algorithm. This algorithm is derived by combining the friends-of-friends
algorithm in the transverse direction and the photometric redshift probability
densities in the radial dimension. The innovative characteristic of our
group-finding algorithm is the improvement of redshift estimation via the
constraints given by the transversely connected galaxies in a group, based on
the assumption that all galaxies in a group have the same redshift. Tests using
the Virgo Consortium Millennium Simulation mock catalogs allow us to show that
the recovery rate of the pFoF algorithm is larger than 80% for mock groups of
at least 2\times10^{13}M_{\sun}, while the false detection rate is about 10%
for pFoF groups containing at least net members. Applying the algorithm
to the CNOC2 group catalogs gives results which are consistent with the mock
catalog tests. From all these results, we conclude that our group-finding
algorithm offers an effective yet simple way to identify galaxy groups in
photometric redshift catalogs.Comment: AJ accepte
Interplay between Kondo suppression and Lifshitz transitions in YbRhSi at high magnetic fields
We investigate the magnetic field dependent thermopower, thermal
conductivity, resistivity and Hall effect in the heavy fermion metal YbRh2Si2.
In contrast to reports on thermodynamic measurements, we find in total three
transitions at high fields, rather than a single one at 10 T. Using the Mott
formula together with renormalized band calculations, we identify Lifshitz
transitions as their origin. The predictions of the calculations show that all
experimental results rely on an interplay of a smooth suppression of the Kondo
effect and the spin splitting of the flat hybridized bands.Comment: 5 pages, 4 figure
Polaronic state and nanometer-scale phase separation in colossal magnetoresistive manganites
High resolution topographic images obtained by scanning tunneling microscope
in the insulating state of Pr0.68Pb0.32MnO3 single crystals showed regular
stripe-like or zigzag patterns on a width scale of 0.4 - 0.5 nm confirming a
high temperature polaronic state. Spectroscopic studies revealed inhomogeneous
maps of zero-bias conductance with small patches of metallic clusters on length
scale of 2 - 3 nm only within a narrow temperature range close to the
metal-insulator transition. The results give a direct observation of polarons
in the insulating state, phase separation of nanometer-scale metallic clusters
in the paramagnetic metallic state, and a homogeneous ferromagnetic state
Variation of elastic scattering across a quantum well
The Drude scattering times of electrons in two subbands of a parabolic
quantum well have been studied at constant electron sheet density and different
positions of the electron distribution along the growth direction. The
scattering times obtained by magnetotransport measurements decrease as the
electrons are displaced towards the well edges, although the lowest-subband
density increases. By comparing the measurements with calculations of the
scattering times of a two-subband system, new information on the location of
the relevant scatterers and the anisotropy of intersubband scattering is
obtained. It is found that the scattering time of electrons in the lower
subband depends sensitively on the position of the scatterers, which also
explains the measured dependence of the scattering on the carrier density. The
measurements indicate segregation of scatterers from the substrate side towards
the quantum well during growth.Comment: 4 pages, 4 figure
Plant-driven variation in decomposition rates improves projections of global litter stock distribution.
Plant litter stocks are critical, regionally for their role in fueling fire
regimes and controlling soil fertility, and globally through their feedback
to atmospheric CO<sub>2</sub> and climate. Here we employ two global databases
linking plant functional types to decomposition rates of wood and leaf
litter (Cornwell et al., 2008; Weedon et al., 2009) to improve future
projections of climate and carbon cycle using an intermediate complexity
Earth System model. Implementing separate wood and leaf litter
decomposabilities and their temperature sensitivities for a range of plant
functional types yielded a more realistic distribution of litter stocks in
all present biomes with the exception of boreal forests and projects a
strong increase in global litter stocks by 35 Gt C and a concomitant small
decrease in atmospheric CO<sub>2</sub> by 3 ppm by the end of this century.
Despite a relatively strong increase in litter stocks, the modified
parameterization results in less elevated wildfire emissions because of a
litter redistribution towards more humid regions
Achieving Efficient and Realistic Full-Radar Simulations and Automatic Data Annotation by Exploiting Ray Meta Data from a Radar Ray Tracing Simulator
In this work, a novel radar simulation concept for efficiently simulating realistic radar data for range, Doppler, and arbitrary antenna positions is introduced. With the concept, the simulated radar signal can also be automatically annotated by splitting it into multiple parts. Annotations that are almost perfect - including the annotation of exotic effects, such as multi-path - can be produced with this approach. Signal parts originating from different parts of an object can be labelled with it as well. To this end, the computation process used in a Monte Carlo shooting and bouncing rays (SBR) simulator is adapted. By considering the hits of each simulated ray, various meta data can be stored, such as hit position, mesh pointer, object IDs, and many more. This collected meta data can then be utilized to predict path-length changes caused by object motion to obtain Doppler information or to apply specific ray filter rules to obtain radar signals that only fulfil specific conditions, such as multiple bounces, or signals that contain specific object IDs. Using this approach, perfect, and otherwise almost impossible, annotation schemes can be realized
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