2,672 research outputs found
Theory for charge and orbital density-wave states in manganite LaSrMnO
We investigate the high temperature phase of layered manganites, and
demonstrate that the charge-orbital phase transition without magnetic order in
LaSrMnO can be understood in terms of the density wave
instability. The orbital ordering is found to be induced by the nesting between
segments of Fermi surface with different orbital characters. The simultaneous
charge and orbital orderings are elaborated with a mean field theory. The
ordered orbitals are shown to be .Comment: published versio
Observational evidence for a spin-up line in the P-Pdot diagram of millisecond pulsars
It is believed that millisecond pulsars attain their fast spins by accreting
matter and angular momentum from companion stars. Theoretical modelling of the
accretion process suggests a spin-up line in the period-period derivative
(-) diagram of millisecond pulsars, which plays an important role
in population studies of radio millisecond pulsars and accreting neutron stars
in X-ray binaries. Here we present observational evidence for such a spin-up
line using a sample of 143 radio pulsars with < 30 ms. We also find that
PSRs~J18233021A and J18242452A, located near the classic spin-up line,
are consistent with the broad population of millisecond pulsars. Finally, we
show that our approach of Bayesian inference can probe accretion physics,
allowing constraints to be placed on the accretion rate and the
disk-magnetosphere interaction.Comment: 10 pages, 4 figures, 2 tables. Accepted for publication by ApJ
A Score-based Geometric Model for Molecular Dynamics Simulations
Molecular dynamics (MD) has long been the \emph{de facto} choice for modeling
complex atomistic systems from first principles, and recently deep learning
become a popular way to accelerate it. Notwithstanding, preceding approaches
depend on intermediate variables such as the potential energy or force fields
to update atomic positions, which requires additional computations to perform
back-propagation. To waive this requirement, we propose a novel model called
ScoreMD by directly estimating the gradient of the log density of molecular
conformations. Moreover, we analyze that diffusion processes highly accord with
the principle of enhanced sampling in MD simulations, and is therefore a
perfect match to our sequential conformation generation task. That is, ScoreMD
perturbs the molecular structure with a conditional noise depending on atomic
accelerations and employs conformations at previous timeframes as the prior
distribution for sampling. Another challenge of modeling such a conformation
generation process is that the molecule is kinetic instead of static, which no
prior studies strictly consider. To solve this challenge, we introduce a
equivariant geometric Transformer as a score function in the diffusion process
to calculate the corresponding gradient. It incorporates the directions and
velocities of atomic motions via 3D spherical Fourier-Bessel representations.
With multiple architectural improvements, we outperforms state-of-the-art
baselines on MD17 and isomers of C7O2H10. This research provides new insights
into the acceleration of new material and drug discovery
Electronic transmission in Graphene suppressed by interlayer interference
We investigate electronic transport property of a graphene monolayer covered
by a graphene nanoribbon. We demonstrate that electronic transmission of a
monolayer can be reduced when covered by a nanoribbon. The transmission
reduction occurs at different energies determined by the width of nanoribbon.
We explain the transmission reduction by using interference between
wavefunctions in the monolayer and the nanoribbon. Furthermore, we show the
transmission reduction of a monolayer is combinable when covered by more than
one nanoribbon and propose a concept of "combination of control" for
nano-application design.Comment: 11 pages, 6 figure
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