2,548 research outputs found
Complete asymptotic expansion of the integrated density of states of multidimensional almost-periodic pseudo-differential operators
We obtain a complete asymptotic expansion of the integrated density of states
of operators of the form H =(-\Delta)^w +B in R^d. Here w >0, and B belongs to
a wide class of almost-periodic self-adjoint pseudo-differential operators of
order less than 2w. In particular, we obtain such an expansion for magnetic
Schr\"odinger operators with either smooth periodic or generic almost-periodic
coefficients.Comment: 47 pages. arXiv admin note: text overlap with arXiv:1004.293
Symmetric achromatic low-beta collider interaction region design concept
We present a new symmetry-based concept for an achromatic low-beta collider
interaction region design. A specially-designed symmetric Chromaticity
Compensation Block (CCB) induces an angle spread in the passing beam such that
it cancels the chromatic kick of the final focusing quadrupoles. Two such CCBs
placed symmetrically around an interaction point allow simultaneous
compensation of the 1st-order chromaticities and chromatic beam smear at the IP
without inducing significant 2nd-order aberrations to the particle trajectory.
We first develop an analytic description of this approach and explicitly
formulate 2nd-order aberration compensation conditions at the interaction
point. The concept is next applied to develop an interaction region design for
the ion collider ring of an electron-ion collider. We numerically evaluate
performance of the design in terms of momentum acceptance and dynamic aperture.
The advantages of the new concept are illustrated by comparing it to the
conventional distributed-sextupole chromaticity compensation scheme.Comment: 12 pages, 17 figures, to be submitted to Phys. Rev. ST Accel. Beam
Titanium trisulfide monolayer: A new direct-gap semiconductor with high and anisotropic carrier mobility
A new two-dimensional (2D) layered material, namely, titanium trisulfide
(TiS) monolayer sheet, is predicted to possess desired electronic
properties for nanoelectronic applications. On basis of the first-principles
calculations within the framework of density functional theory and deformation
theory, we show that the TiS 2D crystal is a direct gap semiconductor with
a band gap of 1.06 eV and high carrier mobility. More remarkably, the in-plane
electron mobility of the 2D TiS is highly anisotropic, amounting to
10,000 cmVs in the \emph{b} direction, which is higher
than that of the MoS monolayer. Meanwhile, the hole mobility is about two
orders of magnitude lower. We also find that bulk TiS possesses lower
cleavage energy than graphite, indicating high possibility of exfoliation for
TiS monolayers or multilayers. Both dynamical and thermal stability of the
TiS monolayer is examined via phonon-spectrum calculation and
Born-Oppenheimer molecular dynamics simulation in \emph{NPT} ensemble. The
predicted novel electronic properties render the TiS monolayer an
attractive 2D material for applications in future nanoelectronics.Comment: 4 figure
Energy bands of atomic monolayers of various materials: Possibility of energy gap engineering
The mobility of graphene is very high because the quantum Hall effects can be
observed even at room temperature. Graphene has the potential of the material
for novel devices because of this high mobility. But the energy gap of graphene
is zero, so graphene can not be applied to semiconductor devices such as
transistors, LEDs, etc. In order to control the energy gaps, we propose atomic
monolayers which consist of various materials besides carbon atoms. To examine
the energy dispersions of atomic monolayers of various materials, we calculated
the electronic states of these atomic monolayers using density functional
theory with structural optimizations. The quantum chemical calculation software
"Gaussian 03" was used under periodic boundary conditions. The calculation
method is LSDA/6-311G(d,p), B3LYP/6-31G(d), or B3LYP/6-311G(d,p). The
calculated materials are C (graphene), Si (silicene), Ge, SiC, GeC, GeSi, BN,
BP, BAs, AlP, AlAs, GaP, and GaAs. These atomic monolayers can exist in the
flat honeycomb shapes. The energy gaps of these atomic monolayers take various
values. Ge is a semimetal; AlP, AlAs, GaP, and GaAs are indirect
semiconductors; and others are direct semiconductors. We also calculated the
change of energy dispersions accompanied by the substitution of the atoms. Our
results suggest that the substitution of impurity atoms for monolayer materials
can control the energy gaps of the atomic monolayers. We conclude that atomic
monolayers of various materials have the potential for novel devices.Comment: This paper was first presented at the 14th International Conference
on Modulated Semiconductor Structures (MSS14) held in Kobe, Japan, on 23 July
200
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