24,422 research outputs found
Momentum Distribution of Near-Zero-Energy Photoelectrons in the Strong-Field Tunneling Ionization in the Long Wavelength Limit
We investigate the ionization dynamics of Argon atoms irradiated by an
ultrashort intense laser of a wavelength up to 3100 nm, addressing the momentum
distribution of the photoelectrons with near-zero-energy. We find a surprising
accumulation in the momentum distribution corresponding to meV energy and a
\textquotedblleft V"-like structure at the slightly larger transverse momenta.
Semiclassical simulations indicate the crucial role of the Coulomb attraction
between the escaping electron and the remaining ion at extremely large
distance. Tracing back classical trajectories, we find the tunneling electrons
born in a certain window of the field phase and transverse velocity are
responsible for the striking accumulation. Our theoretical results are
consistent with recent meV-resolved high-precision measurements.Comment: 5 pages, 4 figure
Negative Link Prediction in Social Media
Signed network analysis has attracted increasing attention in recent years.
This is in part because research on signed network analysis suggests that
negative links have added value in the analytical process. A major impediment
in their effective use is that most social media sites do not enable users to
specify them explicitly. In other words, a gap exists between the importance of
negative links and their availability in real data sets. Therefore, it is
natural to explore whether one can predict negative links automatically from
the commonly available social network data. In this paper, we investigate the
novel problem of negative link prediction with only positive links and
content-centric interactions in social media. We make a number of important
observations about negative links, and propose a principled framework NeLP,
which can exploit positive links and content-centric interactions to predict
negative links. Our experimental results on real-world social networks
demonstrate that the proposed NeLP framework can accurately predict negative
links with positive links and content-centric interactions. Our detailed
experiments also illustrate the relative importance of various factors to the
effectiveness of the proposed framework
On gauge-invariant Green function in 2+1 dimensional QED
Both the gauge-invariant fermion Green function and gauge-dependent
conventional Green function in dimensional QED are studied in the large
limit. In temporal gauge, the infra-red divergence of gauge-dependent
Green function is found to be regulariable, the anomalous dimension is found to
be . This anomalous dimension was argued to be
the same as that of gauge-invariant Green function. However, in Coulomb gauge,
the infra-red divergence of the gauge-dependent Green function is found to be
un-regulariable, anomalous dimension is even not defined, but the infra-red
divergence is shown to be cancelled in any gauge-invariant physical quantities.
The gauge-invariant Green function is also studied directly in Lorentz
covariant gauge and the anomalous dimension is found to be the same as that
calculated in temporal gauge.Comment: 8 pages, 6 figures, to appear in Phys. Rev.
Observation of orbital ordering and origin of the nematic order in FeSe
To elucidate the origin of nematic order in FeSe, we performed
field-dependent 77Se-NMR measurements on single crystals of FeSe. We observed
orbital ordering from the splitting of the NMR spectra and Knight shift and a
suppression of it with magnetic field B0 up to 16 T applied parallel to the
Fe-planes. There is a significant change in the distribution and magnitude of
the internal magnetic field across the orbital ordering temperature Torb while
stripe-type antiferromagnetism is absent. Giant antiferromagnetic (AFM) spin
fluctuations measured by the NMR spin-lattice relaxation are gradually
developed starting at ~ 40 K, which is far below the nematic ordering
temperature Tnem. These results demonstrate that orbital ordering is the origin
of the nematic order, and the AFM spin fluctuation is the driving mechanism of
superconductivity in FeSe under the presence of the nematic order.Comment: 6 pages, 4 figure
Quantum Phase Diffusion in a Small Underdamped Josephson Junction
Quantum phase diffusion in a small underdamped Nb/AlO/Nb junction (
0.4 m) is demonstrated in a wide temperature range of 25-140 mK where
macroscopic quantum tunneling (MQT) is the dominant escape mechanism. We
propose a two-step transition model to describe the switching process in which
the escape rate out of the potential well and the transition rate from phase
diffusion to the running state are considered. The transition rate extracted
from the experimental switching current distribution follows the predicted
Arrhenius law in the thermal regime but is greatly enhanced when MQT becomes
dominant.Comment: 4 pages, 4 figures, 1 tabl
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