169 research outputs found
SadTalker: Learning Realistic 3D Motion Coefficients for Stylized Audio-Driven Single Image Talking Face Animation
Generating talking head videos through a face image and a piece of speech
audio still contains many challenges. ie, unnatural head movement, distorted
expression, and identity modification. We argue that these issues are mainly
because of learning from the coupled 2D motion fields. On the other hand,
explicitly using 3D information also suffers problems of stiff expression and
incoherent video. We present SadTalker, which generates 3D motion coefficients
(head pose, expression) of the 3DMM from audio and implicitly modulates a novel
3D-aware face render for talking head generation. To learn the realistic motion
coefficients, we explicitly model the connections between audio and different
types of motion coefficients individually. Precisely, we present ExpNet to
learn the accurate facial expression from audio by distilling both coefficients
and 3D-rendered faces. As for the head pose, we design PoseVAE via a
conditional VAE to synthesize head motion in different styles. Finally, the
generated 3D motion coefficients are mapped to the unsupervised 3D keypoints
space of the proposed face render, and synthesize the final video. We conduct
extensive experiments to show the superior of our method in terms of motion and
video quality.Comment: Project page: https://sadtalker.github.i
Suppression of Superconductivity by Twin Boundaries in FeSe
Low-temperature scanning tunneling microscopy and spectroscopy are employed
to investigate twin boundaries in stoichiometric FeSe films grown by molecular
beam epitaxy. Twin boundaries can be unambiguously identified by imaging the
90{\deg} change in the orientation of local electronic dimers from Fe site
impurities on either side. Twin boundaries run at approximately 45{\deg} to the
Fe-Fe bond directions, and noticeably suppress the superconducting gap, in
contrast with the recent experimental and theoretical findings in other iron
pnictides. Furthermore, vortices appear to accumulate on twin boundaries,
consistent with the degraded superconductivity there. The variation in
superconductivity is likely caused by the increased Se height in the vicinity
of twin boundaries, providing the first local evidence for the importance of
this height to the mechanism of superconductivity.Comment: 6 pages, 7 figure
Simultaneous electrical-field-effect modulation of both top and bottom Dirac surface states of epitaxial thin films of three-dimensional topological insulators
It is crucial for the studies of the transport properties and quantum effects
related to Dirac surface states of three-dimensional topological insulators (3D
TIs) to be able to simultaneously tune the chemical potentials of both top and
bottom surfaces of a 3D TI thin film. We have realized this in molecular beam
epitaxy-grown thin films of 3D TIs, as well as magnetic 3D TIs, by fabricating
dual-gate structures on them. The films could be tuned between n-type and
p-type by each gate alone. Combined application of two gates can reduce the
carrier density of a TI film to a much lower level than with only one of them
and enhance the film resistance by 10000 %, implying that Fermi level is tuned
very close to the Dirac points of both top and bottom surface states without
crossing any bulk band. The result promises applications of 3D TIs in field
effect devices.Comment: 19 pages, 4 figures, accepted by Nano Letters, forthcomin
Molecular Beam Epitaxy Growth of Superconducting LiFeAs Film on SrTiO3(001) Substrate
The stoichiometric "111" iron-based superconductor, LiFeAs, has attacted
great research interest in recent years. For the first time, we have
successfully grown LiFeAs thin film by molecular beam epitaxy (MBE) on
SrTiO3(001) substrate, and studied the interfacial growth behavior by
reflection high energy electron diffraction (RHEED) and low-temperature
scanning tunneling microscope (LT-STM). The effects of substrate temperature
and Li/Fe flux ratio were investigated. Uniform LiFeAs film as thin as 3
quintuple-layer (QL) is formed. Superconducting gap appears in LiFeAs films
thicker than 4 QL at 4.7 K. When the film is thicker than 13 QL, the
superconducting gap determined by the distance between coherence peaks is about
7 meV, close to the value of bulk material. The ex situ transport measurement
of thick LiFeAs film shows a sharp superconducting transition around 16 K. The
upper critical field, Hc2(0)=13.0 T, is estimated from the temperature
dependent magnetoresistance. The precise thickness and quality control of
LiFeAs film paves the road of growing similar ultrathin iron arsenide films.Comment: 7 pages, 6 figure
Ethyl 6-methyl-3-(2-methylprop-1-enyl)-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate
In the molecule of the title compound, C18H22N2O3, the dihydropyrimidinone ring adopts an envelope conformation. The dihedral angle between the phenyl ring and the mean plane through the enamine fragment is 86.04 (7)°. The molecular conformation is stabilized by an intramolecular C—H⋯O hydrogen bond. In the crystal, intermolecular N—H⋯O hydrogen bonds link pairs of molecules into centrosymmetric dimers
Visualizing the elongated vortices in -Ga nanostrips
We study the magnetic response of superconducting -Ga via low
temperature scanning tunneling microscopy and spectroscopy. The magnetic vortex
cores rely substantially on the Ga geometry, and exhibit an unexpectedly-large
axial elongation with aspect ratio up to 40 in rectangular Ga nano-strips
(width 100 nm). This is in stark contrast with the isotropic circular
vortex core in a larger round-shaped Ga island. We suggest that the unusual
elongated vortices in Ga nanostrips originate from geometric confinement effect
probably via the strong repulsive interaction between the vortices and Meissner
screening currents at the sample edge. Our finding provides novel conceptual
insights into the geometrical confinement effect on magnetic vortices and forms
the basis for the technological applications of superconductors.Comment: published in Phys. Rev. B as a Rapid Communicatio
Imaging the Electron-Boson Coupling in Superconducting FeSe Films Using a Scanning Tunneling Microscope
Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films. The mode appears below Tc as a “dip-hump” feature at energy Ω∼4.7kBTc beyond the superconducting gap Δ. Spectra on strained regions of the FeSe films reveal simultaneous decreases in Δ and Ω. This contrasts with all previous reports on other high-Tc superconductors, where Δ locally anticorrelates with Ω. A local strong coupling model is found to reconcile the discrepancy well, and to provide a unified picture of the electron-boson coupling in unconventional superconductors.Physic
Strong terahertz radiation from a liquid-water line
Terahertz radiation generation from liquid water has long been considered impossible due to strong absorption. A few very recent works reported terahertz generation from water, but the mechanism is not clear and the efficiency demands to be enhanced. We show experimentally that strong single-cycle terahertz radiation with field strength of 0.2MVcm-1 is generated from a water line (or column) of approximately 200μm in diameter irradiated by a mJ femtosecond laser beam. This strength is 100-fold higher than that produced from air using single-color pumping. We attribute the mechanism to the laser-ponderomotive-force-induced current with the symmetry broken around the water-column interface. This mechanism can explain our following observations: the radiation can be generated only when the laser propagation axis deviates from the column center; the deviation determines its field strength and polarity; it is always p polarized no matter whether the laser is p or s polarized. This study provides a simple and efficient scheme of table-top terahertz sources based on liquid water
Atomic and electronic structures of single-layer FeSe on SrTiO3(001): The role of oxygen deficiency
Using first-principles calculation, we propose an interface structure for single triple-layer FeSe on the SrTiO3(001) surface, a high-Tc superconductor found recently. The key component of this structure is the oxygen deficiency on the top layer of the SrTiO3 substrate, as a result of Se etching used in preparing the high-Tc samples. The O vacancies strongly bind the FeSe triple layer to the substrate giving rise to a (2 x 1) reconstruction, as observed by scanning tunneling microscopy. The enhanced binding correlates to the significant increase of Tc observed in experiment. The O vacancies also serve as the source of electron doping, which modifies the Fermi surface of the first FeSe layer by filling the hole pocket near the center of the surface Brillouin zone, as suggested from angle-resolved photoemission spectroscopy measurement
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