661 research outputs found
Quantum Anomalous Hall State in Ferromagnetic SrRuO (111) Bilayers
SrRuO heterostructures grown in the (111) direction are a rare example of
thin film ferromagnets. By means of density functional theory plus dynamical
mean field theory we show that the half-metallic ferromagnetic state with an
ordered magnetic moment of 2/Ru survives the ultimate dimensional
confinement down to a bilayer, even at elevated temperatures of 500K. In
the minority channel, the spin-orbit coupling opens a gap at the linear band
crossing corresponding to filling of the shell. We
demonstrate that the respective state is Haldane's quantum anomalous Hall state
with Chern number =1, without an external magnetic field or magnetic
impurities.Comment: 5 pages, 3 figure
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Valence-programmable nanoparticle architectures.
Nanoparticle-based clusters permit the harvesting of collective and emergent properties, with applications ranging from optics and sensing to information processing and catalysis. However, existing approaches to create such architectures are typically system-specific, which limits designability and fabrication. Our work addresses this challenge by demonstrating that cluster architectures can be rationally formed using components with programmable valence. We realize cluster assemblies by employing a three-dimensional (3D) DNA meshframe with high spatial symmetry as a site-programmable scaffold, which can be prescribed with desired valence modes and affinity types. Thus, this meshframe serves as a versatile platform for coordination of nanoparticles into desired cluster architectures. Using the same underlying frame, we show the realization of a variety of preprogrammed designed valence modes, which allows for assembling 3D clusters with complex architectures. The structures of assembled 3D clusters are verified by electron microcopy imaging, cryo-EM tomography and in-situ X-ray scattering methods. We also find a close agreement between structural and optical properties of designed chiral architectures
Electrostatic traps for dipolar excitons
We consider the design of two-dimensional electrostatic traps for dipolar
indirect excitons. We show that the excitons dipole-dipole interaction,
combined with the in-plane electric fields that arise due to the trap geometry,
constrain the maximal density and lifetime of trapped excitons. We derive an
analytic estimate of these values and determine their dependence on the trap
geometry, thus suggesting the optimal design for high density trapping as a
route for observing excitonic Bose-Einstein condensation.Comment: 5 pages, 3 figures. This 2nd version contains a revised Fig.3 + minor
revisions to the discussion and abstrac
Combinatorial-Entropy-Driven Aggregation in {DNA}-Grafted Nanoparticles
We use computer simulations and experiments to study the interactions between nanoparticles (NPs) grafted with self-complementary DNA strands. Each strand ends with a sticky palindromic single-stranded sequence, allowing it to associate equally favorably with strands grafted on the same particle or on different NPs. Surprisingly we find an attractive interaction between a pair of NPs, and we demonstrate that at low temperature it arises purely from a combinatorial-entropy contribution. We evaluate theoretically and verify numerically this entropic contribution originating from the number of distinct bonding patterns associated with intra- and interparticle binding. This entropic attraction becomes more favorable with decreasing inter-NP distance because more sticky ends can participate in making this choice
Quality flags for GSP-Phot Gaia DR3 astrophysical parameters with machine learning: Effective temperatures case study
Gaia Data Release 3 (DR3) provides extensive information on the astrophysical
properties of stars, such as effective temperature, surface gravity,
metallicity, and luminosity, for over 470 million objects. However, as Gaia's
stellar parameters in GSP-Phot module are derived through model-dependent
methods and indirect measurements, it can lead to additional systematic errors
in the derived parameters. In this study, we compare GSP-Phot effective
temperature estimates with two high-resolution and high signal-to-noise
spectroscopic catalogues: APOGEE DR17 and GALAH DR3, aiming to assess the
reliability of Gaia's temperatures. We introduce an approach to distinguish
good-quality Gaia DR3 effective temperatures using machine-learning methods
such as XGBoost, CatBoost and LightGBM. The models create quality flags, which
can help one to distinguish good-quality GSP-Phot effective temperatures. We
test our models on three independent datasets, including PASTEL, a compilation
of spectroscopically derived stellar parameters from different high-resolution
studies. The results of the test suggest that with these models it is possible
to filter effective temperatures as accurate as 250 K with ~ 90 per cent
precision even in complex regions, such as the Galactic plane. Consequently,
the models developed herein offer a valuable quality assessment tool for
GSP-Phot effective temperatures in Gaia DR3. Consequently, the developed models
offer a valuable quality assessment tool for GSP-Phot effective temperatures in
Gaia DR3. The dataset with flags for all GSP-Phot effective temperature
estimates, is publicly available, as are the models themselves.Comment: 13 pages, 10 figure
Solvent Mediated Assembly of Nanoparticles Confined in Mesoporous Alumina
The controlled self-assembly of thiol stabilized gold nanocrystals in a
mediating solvent and confined within mesoporous alumina was probed in situ
with small angle x-ray scattering. The evolution of the self-assembly process
was controlled reversibly via regulated changes in the amount of solvent
condensed from an undersaturated vapor. Analysis indicated that the
nanoparticles self-assembled into cylindrical monolayers within the porous
template. Nanoparticle nearest-neighbor separation within the monolayer
increased and the ordering decreased with the controlled addition of solvent.
The process was reversible with the removal of solvent. Isotropic clusters of
nanoparticles were also observed to form temporarily during desorption of the
liquid solvent and disappeared upon complete removal of liquid. Measurements of
the absorption and desorption of the solvent showed strong hysteresis upon
thermal cycling. In addition, the capillary filling transition for the solvent
in the nanoparticle-doped pores was shifted to larger chemical potential,
relative to the liquid/vapor coexistence, by a factor of 4 as compared to the
expected value for the same system without nanoparticles.Comment: 9 pages, 9 figures, appeared in Phys. Rev.
Verification of Photometric Parallaxes with Gaia DR2 Data
Results of comparison of Gaia DR2 parallaxes with data derived from a
combined analysis of 2MASS (Two Micron All-Sky Survey), SDSS (Sloan Digital Sky
Survey), GALEX (Galaxy Evolution Explorer), and UKIDSS (UKIRT Infrared Deep Sky
Survey) surveys in four selected high-latitude sky areas are
presented. It is shown that multicolor photometric data from large modern
surveys can be used for parameterization of stars closer than 4400 pc and
brighter than , including estimation of parallax and
interstellar extinction value. However, the stellar luminosity class should be
properly determined.Comment: 11 pages, 5 figure
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