2,469 research outputs found
Resonant inelastic x-ray scattering (RIXS) spectra of magnesium diboride
Using the tight-binding linear muffin-tin orbitals method, the soft x-ray
fluorescence K-emission spectra of boron in MgB_2, excited close to the
absorption edge, are estimated. In the calculations the angle of incidence
between the direction of the incoming photon and the hexagonal axis of the
specimen is 60 degrees and 75 degrees. Comparison with experiment is possible
in the former case where good agreement is found. Furthermore, another resonant
feature below the Fermi energy is predicted for the larger angle. This feature
can be related to the excitations to the antibonding B pi-band in the
neighbourhood of the L-H line in the Brillouin zone.Comment: 4 pages with 4 figure
Evolution of high-frequency gravitational waves in some cosmological models
We investigate Isaacson's high-frequency gravitational waves which propagate
in some relevant cosmological models, in particular the FRW spacetimes. Their
time evolution in Fourier space is explicitly obtained for various metric forms
of (anti--)de Sitter universe. Behaviour of high-frequency waves in the
anisotropic Kasner spacetime is also described.Comment: 14 pages, 8 figures, to appear in Czech. J. Phy
Nodal Quasiparticle Dispersion in Strongly Correlated d-wave Superconductors
We analyze the effects of a momentum-dependent self-energy on the
photoemission momentum distribution curve (MDC) lineshape, dispersion and
linewidth. We illustrate this general analysis by a detailed examination of
nodal quasiparticles in high Tc cuprates. We use variational results for the
nodal quasiparticle weight Z (which varies rapidly with hole doping x) and the
low energy Fermi velocity (which is independent of x), to show that
the high energy MDC dispersion , so that it is much
larger than the bare (band structure) velocity and also increases strongly with
underdoping. We also present arguments for why the low energy Fermi velocity
and the high energy dispersion are independent of the bare band structure at
small x. All of these results are in good agreement with earlier and recent
photoemission data [Zhou et al, Nature 423, 398 (2003)].Comment: 4 pages, 3 eps fig
Squeezing based on nondegenerate frequency doubling internal to a realistic laser
We investigate theoretically the quantum fluctuations of the fundamental
field in the output of a nondegenerate second harmonic generation process
occuring inside a laser cavity. Due to the nondegenerate character of the
nonlinear medium, a field orthogonal to the laser field is for some operating
conditions indepedent of the fluctuations produced by the laser medium. We show
that this fact may lead to perfect squeezing for a certain polarization mode of
the fundamental field. The experimental feasibility of the system is also
discussed.Comment: 6 pages, 5 figure
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InGaAs 3D MOSFETs with Drastically Different Shapes Formed by Anisotropic Wet Etching
In this work, we report on a 3D device fabrication technology achieved by applying a novel anisotropic wet etching method. By aligning channel structures along different crystal orientations, high performance 3D InGaAs devices with different channel shapes such as fins, nanowires and waves have been demonstrated. With further optimizing off-state leakage path by barrier engineering, a record high ION/IOFF over 10(8) and minimum I OFF~3pA/um have been obtained from InGaAs FinFET device. Scaling metrics for InGaAs GAA MOSFETs and FinFETs are systematically studied with Lch from 800 nm down to 50 nm and WFin/WNW from 100 nm down to 20 nm which shows an excellent immunity to short channel effects.Chemistry and Chemical Biolog
Sharp two-sided heat kernel estimates for critical Schr\"odinger operators on bounded domains
On a smooth bounded domain \Omega \subset R^N we consider the Schr\"odinger
operators -\Delta -V, with V being either the critical borderline potential
V(x)=(N-2)^2/4 |x|^{-2} or V(x)=(1/4) dist (x,\partial\Omega)^{-2}, under
Dirichlet boundary conditions. In this work we obtain sharp two-sided estimates
on the corresponding heat kernels. To this end we transform the Scr\"odinger
operators into suitable degenerate operators, for which we prove a new
parabolic Harnack inequality up to the boundary. To derive the Harnack
inequality we have established a serier of new inequalities such as improved
Hardy, logarithmic Hardy Sobolev, Hardy-Moser and weighted Poincar\'e. As a
byproduct of our technique we are able to answer positively to a conjecture of
E.B.Davies.Comment: 40 page
Infrared problem for the Nelson model on static space-times
We consider the Nelson model with variable coefficients and investigate the
problem of existence of a ground state and the removal of the ultraviolet
cutoff. Nelson models with variable coefficients arise when one replaces in the
usual Nelson model the flat Minkowski metric by a static metric, allowing also
the boson mass to depend on position. A physical example is obtained by
quantizing the Klein-Gordon equation on a static space-time coupled with a
non-relativistic particle. We investigate the existence of a ground state of
the Hamiltonian in the presence of the infrared problem, i.e. assuming that the
boson mass tends to 0 at infinity
Entangled light in transition through the generation threshold
We investigate continuous variable entangling resources on the base of
two-mode squeezing for all operational regimes of a nondegenerate optical
parametric oscillator with allowance for quantum noise of arbitrary level. The
results for the quadrature variances of a pair of generated modes are obtained
by using the exact steady-state solution of Fokker-Planck equation for the
complex P-quasiprobability distribution function. We find a simple expression
for the squeezed variances in the near-threshold range and conclude that the
maximal two-mode squeezing reaches 50% relative to the level of vacuum
fluctuations and is achieved at the pump field intensity close to the
generation threshold. The distinction between the degree of two-mode squeezing
for monostable and bistable operational regimes is cleared up.Comment: 7 pages, 4 figures; Content changed: more details added to the
discussion. To be published in Phys. Rev.
How to Create an Innovation Accelerator
Too many policy failures are fundamentally failures of knowledge. This has
become particularly apparent during the recent financial and economic crisis,
which is questioning the validity of mainstream scholarly paradigms. We propose
to pursue a multi-disciplinary approach and to establish new institutional
settings which remove or reduce obstacles impeding efficient knowledge
creation. We provided suggestions on (i) how to modernize and improve the
academic publication system, and (ii) how to support scientific coordination,
communication, and co-creation in large-scale multi-disciplinary projects. Both
constitute important elements of what we envision to be a novel ICT
infrastructure called "Innovation Accelerator" or "Knowledge Accelerator".Comment: 32 pages, Visioneer White Paper, see http://www.visioneer.ethz.c
Polarons with a twist
We consider a polaron model where molecular \emph{rotations} are important.
Here, the usual hopping between neighboring sites is affected directly by the
electron-phonon interaction via a {\em twist-dependent} hopping amplitude. This
model may be of relevance for electronic transport in complex molecules and
polymers with torsional degrees of freedom, such as DNA, as well as in
molecular electronics experiments where molecular twist motion is significant.
We use a tight-binding representation and find that very different polaronic
properties are already exhibited by a two-site model -- these are due to the
nonlinearity of the restoring force of the twist excitations, and of the
electron-phonon interaction in the model. In the adiabatic regime, where
electrons move in a {\em low}-frequency field of twisting-phonons, the
effective splitting of the energy levels increases with coupling strength. The
bandwidth in a long chain shows a power-law suppression with coupling, unlike
the typical exponential dependence due to linear phonons.Comment: revtex4 source and one eps figur
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