2,773 research outputs found
Carrier Plasmon Induced Nonlinear Band Gap Renormalization in Two-Dimensional Semiconductors
In reduced-dimensional semiconductors, doping-induced carrier plasmons can
strongly couple with quasiparticle excitations, leading to a significant band
gap renormalization. We develop a new plasmon-pole theory that efficiently and
accurately capture this coupling. Using monolayer molybdenum disulfide (MoS2)
as a prototype two-dimensional (2D) semiconductor, we reveal an enhanced band
gap renormalization around 400 meV and an unusual nonlinear evolution of its
band gap with doping. This 2D prediction significantly differs from the linear
behaviors that are common to one-dimensional structures. Our developed approach
allows for a quantitative understanding of many-body interactions in general
doped 2D semiconductors and paves the way for novel band gap engineering
techniques
Multidimensional BSDEs with uniformly continuous coefficients: the general result
In this paper, by introducing a new notion of envelope of the stochastic
process, we construct a family of random differential equations whose solutions
can be viewed as solutions of a family of ordinary differential equations and
prove that the multidimensional backward stochastic differential equations
(BSDEs for short) with the general uniformly continuous coefficients are
uniquely solvable. As a result, we solve the open problem of multidimensional
BSDEs with uniformly continuous coefficients.Comment: 20 page
Superconvergence of Numerical Gradient for Weak Galerkin Finite Element Methods on Nonuniform Cartesian Partitions in Three Dimensions
A superconvergence error estimate for the gradient approximation of the
second order elliptic problem in three dimensions is analyzed by using weak
Galerkin finite element scheme on the uniform and non-uniform cubic partitions.
Due to the loss of the symmetric property from two dimensions to three
dimensions, this superconvergence result in three dimensions is not a trivial
extension of the recent superconvergence result in two dimensions
\cite{sup_LWW2018} from rectangular partitions to cubic partitions. The error
estimate for the numerical gradient in the -norm arrives at a
superconvergence order of when the lowest
order weak Galerkin finite elements consisting of piecewise linear polynomials
in the interior of the elements and piecewise constants on the faces of the
elements are employed. A series of numerical experiments are illustrated to
confirm the established superconvergence theory in three dimensions.Comment: 31 pages, 24 table
Exciton Energy Spectra in Two-Dimensional Graphene Derivatives
The energy spectra and wavefunctions of bound excitons in important
two-dimensional (2D) graphene derivatives, i.e., graphyne and graphane, are
found to be strongly modified by quantum confinement, making them qualitatively
different from the usual Rydberg series. However, their parity and optical
selection rules are preserved. Thus a one-parameter modified hydrogenic model
is applied to quantitatively explain the ab initio exciton spectra, and allows
one to extrapolate the electron-hole binding energy from optical spectroscopies
of 2D semiconductors without costly simulations. Meanwhile, our calculated
optical absorption spectrum and enhanced spin singlet-triplet splitting project
graphyne, an allotrope of graphene, as a candidate for intriguing energy and
biomedical applications
-coordinated modules for vertex algebras
We study -coordinated modules for vertex algebras, where
with an integer parameter is a family of associates
of the one-dimensional additive formal group. As the main results, we obtain a
Jacobi type identity and a commutator formula for -coordinated
modules. We then use these results to study -coordinated modules
for vertex algebras associated to Novikov algebras by Primc.Comment: late
Constraining cosmological parameters in FLRW metric with lensed GW+EM signals
We proposed a model-independent method to constrain the cosmological
parameters using the Distance Sum Rule of the FLRW metric by combining the time
delay distances and the comoving distances through a multi-messenger approach.
The time delay distances are measured from lensed gravitational wave~(GW)
signals together with their corresponding electromagnetic wave~(EM)
counterpart, while the comoving distances are obtained from a parametrized
fitting approach with independent supernova observations. With a series of
simulations based on Einstein Telescope, Large Synoptic Survey Telescope and
The Dark Energy Survey, we find that only 10 lensed GW+EM systems can achieve
the constraining power comparable to and even stronger than 300 lensed quasar
systems due to more precise time delay from lensed GW signals. Specifically,
the cosmological parameters can be constrained to ~ and
~ (1). Our results show that more precise
time delay measurements could provide more stringent cosmological parameter
values, and lensed GW+EM systems therefore can be applied as a powerful tool in
the future precision cosmology.Comment: Accepted for publication in The Astrophysical Journa
Effective numerical treatment of sub-diffusion equation with non-smooth solution
In this paper we investigate a sub-diffusion equation for simulating the
anomalous diffusion phenomenon in real physical environment. Based on an
equivalent transformation of the original sub-diffusion equation followed by
the use of a smooth operator, we devise a high-order numerical scheme by
combining the Nystrom method in temporal direction with the compact finite
difference method and the spectral method in spatial direction. The distinct
advantage of this approach in comparison with most current methods is its high
convergence rate even though the solution of the anomalous sub-diffusion
equation usually has lower regularity on the starting point. The effectiveness
and efficiency of our proposed method are verified by several numerical
experiments.Comment: 15 pages, 6 figure
Quasiparticle band-edge energy and band offsets of monolayer of molybdenum and tungsten chalcogenide
We report the quasiparticle energy of monolayer of molybdenum and tungsten
dichalcogenides, MX2 (M=Mo, W; X=S, Se, Te). Beyond calculating bandgaps, we
have achieved converged absolute band energies relative to the vacuum level.
Compared with the results from other approaches, the GW calculation reveals
substantially larger bandgaps and different absolute band energies because of
enhanced many-electron effects. Interestingly, our fully-converged
quasiparticle energies ratify the band-gap-center approximation, making it a
convenient way to estimate quasiparticle energy. The absolute quasiparticle
energies and band offsets obtained in this work are important for designing
heterojunction devices and chemical catalysts based on monolayer
dichalcogenides
Pressure Tuned Enhancement of Superconductivity and Change of Ground State Properties in LaO0.5F0.5BiSe2 Single Crystals
By using a hydrostatic pressure, we have successfully tuned the ground state
and superconductivity in LaO0.5F0.5BiSe2 single crystals. It is found that,
with the increase of pressure, the original superconducting phase with Tc about
3.5 K can be tuned to a state with lower Tc, and then a new superconducting
phase with Tc about 6.5 K emerges. Accompanied by this crossover, the ground
state is switched from a semiconducting state to a metallic one. Accordingly,
the normal state resistivity also shows a nonmonotonic change with the external
pressure. Furthermore, by applying a magnetic field, the new superconducting
state under pressure with Tc about 6.5 K is suppressed, and the normal state
reveals a weak semiconducting feature again. These results illustrate a
non-trivial relationship between the normal state property and
superconductivity in this newly discovered superconducting system.Comment: 6 pages, 4 figure
Provably size-guaranteed mesh generation with superconvergence
The properties and applications of superconvergence on size-guaranteed
Delaunay triangulation generated by bubble placement method (BPM), are studied
in this paper. First, we derive a mesh condition that the difference between
the actual side length and the desired length is as small as . Second, the superconvergence estimations
are analyzed on linear and quadratic finite element for elliptic boundary value
problem based on the above mesh condition. In particular, the mesh condition is
suitable for many known superconvergence estimations of different equations.
Numerical tests are provided to verify the theoretical findings and to exhibit
the superconvergence property on BPM-based grids
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