1,258 research outputs found
Electrical current-driven pinhole formation and insulator-metal transition in tunnel junctions
Current Induced Resistance Switching (CIS) was recently observed in thin
tunnel junctions (TJs) with ferromagnetic (FM) electrodes and attributed to
electromigration of metallic atoms in nanoconstrictions in the insulating
barrier. The CIS effect is here studied in TJs with two thin (20 \AA)
non-magnetic (NM) Ta electrodes inserted above and below the insulating
barrier. We observe resistance (R) switching for positive applied electrical
current (flowing from the bottom to the top lead), characterized by a
continuous resistance decrease and associated with current-driven displacement
of metallic ions from the bottom electrode into the barrier (thin barrier
state). For negative currents, displaced ions return into their initial
positions in the electrode and the electrical resistance gradually increases
(thick barrier state). We measured the temperature (T) dependence of the
electrical resistance of both thin- and thick-barrier states ( and R
respectively). Experiments showed a weaker R(T) variation when the tunnel
junction is in the state, associated with a smaller tunnel contribution.
By applying large enough electrical currents we induced large irreversible
R-decreases in the studied TJs, associated with barrier degradation. We then
monitored the evolution of the R(T) dependence for different stages of barrier
degradation. In particular, we observed a smooth transition from tunnel- to
metallic-dominated transport. The initial degradation-stages are related to
irreversible barrier thickness decreases (without the formation of pinholes).
Only for later barrier degradation stages do we have the appearance of metallic
paths between the two electrodes that, however, do not lead to metallic
dominated transport for small enough pinhole radius.Comment: 10 pages, 3 figure
Iordanskii Force and the Gravitational Aharonov-Bohm effect for a Moving Vortex
I discuss the scattering of phonons by a vortex moving with respect to a
superfluid condensate. This allows us to test the compatibility of the
scattering-theory derivation of the Iordanskii force with the galilean
invariance of the underlying fluid dynamics. In order to obtain the correct
result we must retain terms in the sound-wave equation, and this
reinforces the interpretation, due to Volovik, of the Iordanskii force as an
analogue of the gravitational Bohm-Aharonov effect.Comment: 20 pages, LaTe
Neutral Collective Excitations in Striped Hall States
In the striped Hall state, a magnetic translation in one direction is
spontaneously broken to the discrete translation. The spectrum of the neutral
collective excitation is obtained in the single mode approximation at
half-filled third and fourth Landau levels. The spectrum is anisotropic and has
a multiple line node structure. In one direction, the spectrum resembles the
liquid Helium spectrum with the phonon and roton minimum.Comment: 2 pages, 2 figures, LT23 Hiroshim
Deep Video Generation, Prediction and Completion of Human Action Sequences
Current deep learning results on video generation are limited while there are
only a few first results on video prediction and no relevant significant
results on video completion. This is due to the severe ill-posedness inherent
in these three problems. In this paper, we focus on human action videos, and
propose a general, two-stage deep framework to generate human action videos
with no constraints or arbitrary number of constraints, which uniformly address
the three problems: video generation given no input frames, video prediction
given the first few frames, and video completion given the first and last
frames. To make the problem tractable, in the first stage we train a deep
generative model that generates a human pose sequence from random noise. In the
second stage, a skeleton-to-image network is trained, which is used to generate
a human action video given the complete human pose sequence generated in the
first stage. By introducing the two-stage strategy, we sidestep the original
ill-posed problems while producing for the first time high-quality video
generation/prediction/completion results of much longer duration. We present
quantitative and qualitative evaluation to show that our two-stage approach
outperforms state-of-the-art methods in video generation, prediction and video
completion. Our video result demonstration can be viewed at
https://iamacewhite.github.io/supp/index.htmlComment: Under review for CVPR 2018. Haoye and Chunyan have equal contributio
The BCS-like gap in superconductor SmFeAsO_0.85F_0.15
Since the discovery of superconductivity in the cuprates two decades ago, it
has been firmly established that the CuO_2 plane is consequential for high T_C
superconductivity and a host of other very unusual properties. A new family of
superconductors with the general composition of LaFeAsO_(1-x)F_x has recently
been discovered but with the conspicuous lacking of the CuO_2 planes, thus
raising the tantalizing questions of the different pairing mechanisms in these
oxypnictide superconductors. Intimately related to pairing in a superconductor
are the superconducting gap, its value, structure, and temperature dependence.
Here we report the observation of a single gap in the superconductor
SmFeAsO_0.85F_0.15 with T_C = 42 K as measured by Andreev spectroscopy. The gap
value of 2Delta = 13.34+/-0.3 meV gives 2Delta/k_BT_C = 3.68, close to the BCS
prediction of 3.53. The gap decreases with temperature and vanishes at T_C in a
manner consistent with the Bardeen-Cooper-Schrieffer (BCS) prediction but
dramatically different from that of the pseudogap behavior in the cuprate
superconductors. Our results clearly indicate a nodeless gap order parameter,
which is nearly isotropic in size across different sections of the Fermi
surface, and are not compatible with models involving antiferromagnetic
fluctuations, strong correlations, t-J model, and the like, originally designed
for cuprates.Comment: 8 pages, 3 figure
Ballistic and Diffuse Electron Transport in Nanocontacts of Magnetics
The transition from the ballistic electron transport to the diffuse one is
experimentally observed in the study of the magnetic phase transition in Ni
nanocontacts with different sizes. It is shown that the voltage needed
for Joule heating of the near-contact region to the critical temperature does
not depend on the contact size only in the diffuse mode. For the ballistic
contact it increases with decrease in the nanocontact size. The reduction of
the transport electron mean free path due to heating of NCs may result in
change of the electron transport mode from ballistic to diffusive one.Comment: 7 pages, 2 figures accepted for the publication in JETPL
(http://www.jetpletters.ac.ru). Will be published on 25 april 201
Magnetic field processing to enhance critical current densities of MgB2 superconductors
Magnetic field of up to 12 T was applied during the sintering process of pure
MgB2 and carbon nanotube (CNT) doped MgB2 wires. We have demonstrated that
magnetic field processing results in grain refinement, homogeneity and
significant enhancement in Jc(H) and Hirr. The Jc of pure MgB2 wire increased
by up to a factor of 3 to 4 and CNT doped MgB2 by up to an order of magnitude
in high field region respectively, compared to that of the non-field processed
samples. Hirr for CNT doped sample reached 7.7 T at 20 K. Magnetic field
processing reduces the resistivity in CNT doped MgB2, straightens the entangled
CNT and improves the adherence between CNTs and MgB2 matrix. No crystalline
alignment of MgB2 was observed. This method can be easily scalable for a
continuous production and represents a new milestone in the development of MgB2
superconductors and related systems
Longitudinal Force on a Moving Potential
We show a formal result of the longitudinal force acting on a moving
potential. The potential can be velocity-dependent, which appears in various
interesting physical systems, such as electrons in the presence of a magnetic
flux-line, or phonons scattering off a moving vortex. By using the phase-shift
analysis, we are able to show the equivalence between the adiabatic
perturbation theory and the kinetic theory for the longitudinal force in the
dilute gas limit.Comment: RevTeX, 4 pages, revised tex
Learning Joint Spatial-Temporal Transformations for Video Inpainting
High-quality video inpainting that completes missing regions in video frames
is a promising yet challenging task. State-of-the-art approaches adopt
attention models to complete a frame by searching missing contents from
reference frames, and further complete whole videos frame by frame. However,
these approaches can suffer from inconsistent attention results along spatial
and temporal dimensions, which often leads to blurriness and temporal artifacts
in videos. In this paper, we propose to learn a joint Spatial-Temporal
Transformer Network (STTN) for video inpainting. Specifically, we
simultaneously fill missing regions in all input frames by self-attention, and
propose to optimize STTN by a spatial-temporal adversarial loss. To show the
superiority of the proposed model, we conduct both quantitative and qualitative
evaluations by using standard stationary masks and more realistic moving object
masks. Demo videos are available at https://github.com/researchmm/STTN.Comment: Accepted by ECCV202
Universal Equilibrium Currents in the Quantum Hall Fluid
The equilibrium current distribution in a quantum Hall fluid that is
subjected to a slowly varying confining potential is shown to generally consist
of strips or channels of current, which alternate in direction, and which have
universal integrated strengths. A measurement of these currents would yield
direct independent measurements of the proper quasiparticle and quasihole
energies in the fractional quantum Hall states.Comment: 4 pages, Revte
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