331 research outputs found
Metallicity of the SrTiO3 surface induced by room temperature evaporation of alumina
It is shown that a metallic state can be induced on the surface of SrTiO3
crystals by the electron beam evaporation of oxygen deficient alumina or
insulating granular aluminium. No special preparation nor heating of the SrTiO3
surface is needed. Final metallic or insulating states can be obtained
depending on the oxygen pressure during the evaporation process.
Photoconductivity and electrical field effect are also demonstrated.Comment: 8 pages, 3 figure
Electronically coupled complementary interfaces between perovskite band insulators
Perovskite oxides exhibit a plethora of exceptional electronic properties,
providing the basis for novel concepts of oxide-electronic devices. The
interest in these materials is even extended by the remarkable characteristics
of their interfaces. Studies on single epitaxial connections between the two
wide-bandgap insulators LaAlO3 and SrTiO3 have revealed them to be either
high-mobility electron conductors or insulating, depending on the atomic
stacking sequences. In the latter case they are conceivably positively charged.
For device applications, as well as for basic understanding of the interface
conduction mechanism, it is important to investigate the electronic coupling of
closely-spaced complementary interfaces. Here we report the successful
realization of such electronically coupled complementary interfaces in SrTiO3 -
LaAlO3 thin film multilayer structures, in which the atomic stacking sequence
at the interfaces was confirmed by quantitative transmission electron
microscopy. We found a critical separation distance of 6 perovskite unit cell
layers, corresponding to approximately 2.3 nm, below which a decrease of the
interface conductivity and carrier density occurs. Interestingly, the high
carrier mobilities characterizing the separate electron doped interfaces are
found to be maintained in coupled structures down to sub-nanometer interface
spacing
Understanding the nature of electronic effective mass in double-doped SrTiO
We present an approach to tune the effective mass in an oxide semiconductor
by a double doping mechanism. We demonstrate this in a model oxide system
SrLaTiO, where we can tune the effective mass ranging
from 6--20 as a function of filling or carrier concentration and
the scattering mechanism, which are dependent on the chosen lanthanum and
oxygen vacancy concentrations. The effective mass values were calculated from
the Boltzmann transport equation using the measured transport properties of
thin films of SrLaTiO. Our method, which shows that
the effective mass decreases with carrier concentration, provides a means for
understanding the nature of transport processes in oxides, which typically have
large effective mass and low electron mobility, contrary to the tradional high
mobility semiconductors.Comment: 5 pages with 4 figure
Overfitting for Fun and Profit: Instance-Adaptive Data Compression
Neural data compression has been shown to outperform classical methods in
terms of performance, with results still improving rapidly. At a high
level, neural compression is based on an autoencoder that tries to reconstruct
the input instance from a (quantized) latent representation, coupled with a
prior that is used to losslessly compress these latents. Due to limitations on
model capacity and imperfect optimization and generalization, such models will
suboptimally compress test data in general. However, one of the great strengths
of learned compression is that if the test-time data distribution is known and
relatively low-entropy (e.g. a camera watching a static scene, a dash cam in an
autonomous car, etc.), the model can easily be finetuned or adapted to this
distribution, leading to improved performance. In this paper we take this
concept to the extreme, adapting the full model to a single video, and sending
model updates (quantized and compressed using a parameter-space prior) along
with the latent representation. Unlike previous work, we finetune not only the
encoder/latents but the entire model, and - during finetuning - take into
account both the effect of model quantization and the additional costs incurred
by sending the model updates. We evaluate an image compression model on
I-frames (sampled at 2 fps) from videos of the Xiph dataset, and demonstrate
that full-model adaptation improves performance by ~1 dB, with respect to
encoder-only finetuning.Comment: Accepted at International Conference on Learning Representations 202
Magnetic effects at the interface between nonmagnetic oxides
The electronic reconstruction at the interface between two insulating oxides
can give rise to a highly-conductive interface. In analogy to this remarkable
interface-induced conductivity we show how, additionally, magnetism can be
induced at the interface between the otherwise nonmagnetic insulating
perovskites SrTiO3 and LaAlO3. A large negative magnetoresistance of the
interface is found, together with a logarithmic temperature dependence of the
sheet resistance. At low temperatures, the sheet resistance reveals magnetic
hysteresis. Magnetic ordering is a key issue in solid-state science and its
underlying mechanisms are still the subject of intense research. In particular,
the interplay between localized magnetic moments and the spin of itinerant
conduction electrons in a solid gives rise to intriguing many-body effects such
as Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, the Kondo effect, and
carrier-induced ferromagnetism in diluted magnetic semiconductors. The
conducting oxide interface now provides a versatile system to induce and
manipulate magnetic moments in otherwise nonmagnetic materials.Comment: Nature Materials, July issu
The effect of walking speed on quality of gait in older adults
Background: Gait quality characteristics can contribute to the identification of individuals at risk of falls. Since older adults with high fall risk tend to walk slower than older adults with a lower fall risk, walking speed may underlie differences in gait quality characteristics. Research question: How does walking speed affect gait quality characteristics in older people? Methods: We investigated the effect of walking speed on gait characteristics in 11 older adults (aged 69.6 ± 4.1 years). Trunk accelerations (Dynaport MoveMonitor) were recorded during 5 min of treadmill walking at four different speeds. From these trunk accelerations we calculated step frequency, root mean square, harmonic ratio, index of harmonicity, sample entropy and logarithmic divergence rate per stride. Results: Our results showed that all gait characteristics were affected by walking speed, except for sample entropy in antero-posterior (AP) direction. An increase in walking speed resulted in a higher step frequency, higher standard deviation, more symmetric gait, more smooth vertical (VT) accelerations, less smooth accelerations in medio-lateral (ML) and AP directions, less regular dynamics in ML direction, more regular dynamics in VT direction, and a more stable gait pattern overall. Significance: These findings suggest that, within a range of 0.5–1.4 m/s, a lower walking speed results in a lower gait quality, which may underlie differences in gait quality between older fallers and non-fallers
Learning Sampling and Model-Based Signal Recovery for Compressed Sensing MRI
Compressed sensing (CS) MRI relies on adequate undersampling of the k-space
to accelerate the acquisition without compromising image quality. Consequently,
the design of optimal sampling patterns for these k-space coefficients has
received significant attention, with many CS MRI methods exploiting
variable-density probability distributions. Realizing that an optimal sampling
pattern may depend on the downstream task (e.g. image reconstruction,
segmentation, or classification), we here propose joint learning of both
task-adaptive k-space sampling and a subsequent model-based proximal-gradient
recovery network. The former is enabled through a probabilistic generative
model that leverages the Gumbel-softmax relaxation to sample across trainable
beliefs while maintaining differentiability. The proposed combination of a
highly flexible sampling model and a model-based (sampling-adaptive) image
reconstruction network facilitates exploration and efficient training, yielding
improved MR image quality compared to other sampling baselines
Suppression of Octahedral Tilts and Associated Changes of Electronic Properties at Epitaxial Oxide Heterostructure Interfaces
Epitaxial oxide interfaces with broken translational symmetry have emerged as
a central paradigm behind the novel behaviors of oxide superlattices. Here, we
use scanning transmission electron microscopy to demonstrate a direct,
quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen
octahedral rotations across the BiFeO3-La0.7Sr0.3MnO3 interface to elucidate
how the change of crystal symmetry is accommodated. Combined with low-loss
electron energy loss spectroscopy imaging, we demonstrate a mesoscopic
antiferrodistortive phase transition and elucidate associated changes in
electronic properties in a thin layer directly adjacent to the interface
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