1,260 research outputs found
Application of dynamical systems theory to the high angle of attack dynamics of the F-14
Strain-Dependence of Surface Diffusion: Ag on Ag(111) and Pt(111)
Using density-functional theory with the local-density approximation and the
generalized gradient approximation we compute the energy barriers for surface
diffusion for Ag on Pt(111), Ag on one monolayer of Ag on Pt(111), and Ag on
Ag(111). The diffusion barrier for Ag on Ag(111) is found to increase linearly
with increasing lattice constant. We also discuss the reconstruction that has
been found experimentally when two Ag layers are deposited on Pt(111). Our
calculations explain why this strain driven reconstruction occurs only after
two Ag layers have been deposited.Comment: 4 pages, 3 figures, Phys. Rev. B 55 (1997), in pres
Linear Collider Capabilities for Supersymmetry in Dark Matter Allowed Regions of the mSUGRA Model
Recent comparisons of minimal supergravity (mSUGRA) model predictions with
WMAP measurements of the neutralino relic density point to preferred regions of
model parameter space. We investigate the reach of linear colliders (LC) with
and 1 TeV for SUSY in the framework of the mSUGRA model. We find
that LCs can cover the entire stau co-annihilation region provided \tan\beta
\alt 30. In the hyperbolic branch/focus point (HB/FP) region of parameter
space, specialized cuts are suggested to increase the reach in this important
``dark matter allowed'' area. In the case of the HB/FP region, the reach of a
LC extends well past the reach of the CERN LHC. We examine a case study in the
HB/FP region, and show that the MSSM parameters and can be
sufficiently well-measured to demonstrate that one would indeed be in the HB/FP
region, where the lightest chargino and neutralino have a substantial higgsino
component.Comment: 29 pages, 15 EPS figures; updated version slightly modified to
conform with published versio
Localization in Strongly Chaotic Systems
We show that, in the semiclassical limit and whenever the elements of the
Hamiltonian matrix are random enough, the eigenvectors of strongly chaotic
time-independent systems in ordered bases can on average be exponentially
localized across the energy shell and decay faster than exponentially outside
the energy shell. Typically however, matrix elements are strongly correlated
leading to deviations from such behavior.Comment: RevTeX, 5 pages + 3 postscript figures, submitted to Phys. Rev. Let
Phase space geometry and slow dynamics
We describe a non-Arrhenius mechanism for slowing down of dynamics that is
inherent to the high dimensionality of the phase space. We show that such a
mechanism is at work both in a family of mean-field spin-glass models without
any domain structure and in the case of ferromagnetic domain growth. The
marginality of spin-glass dynamics, as well as the existence of a `quasi
equilibrium regime' can be understood within this scenario. We discuss the
question of ergodicity in an out-of equilibrium situation.Comment: 23 pages, ReVTeX3.0, 6 uuencoded postscript figures appende
The Essential Interactions in Oxides and Spectral Weight Transfer in Doped Manganites
We calculate the value of the Fr\"ohlich electron-phonon interaction in
manganites, cuprates, and some other charge-transfer insulators and show that
this interaction is much stronger than any relevant magnetic interaction. A
polaron shift due to the Fr\"ohlich interaction, which is about 1 eV, suggests
that carriers in those systems are small (bi)polarons at all temperatures and
doping levels, in agreement with the oxygen isotope effect and other data. An
opposite conclusion, recently suggested in the literature, is shown to be
incorrect. The frequency and temperature dependence of the optical conductivity
of ferromagnetic manganites is explained within the framework of the bipolaron
theory.Comment: 6 pages, REVTeX 3.1 with 3 eps-figures. Journal versio
Noncommutative Dipole Field Theories And Unitarity
We extend the argument of Gomis and Mehen for violation of unitarity in field
theories with space-time noncommutativity to dipole field theories. In dipole
field theories with a timelike dipole vector, we present 1-loop amplitudes that
violate the optical theorem. A quantum mechanical system with nonlocal
potential of finite extent in time also shows violation of unitarity.Comment: typos corrected, more details added in Sec 5, version to appear in
JHE
On the Resolution of the Time-Like Singularities in Reissner-Nordstrom and Negative-Mass Schwarzschild
Certain time-like singularities are shown to be resolved already in classical
General Relativity once one passes from particle probes to scalar waves. The
time evolution can be defined uniquely and some general conditions for that are
formulated. The Reissner-Nordstrom singularity allows for communication through
the singularity and can be termed "beam splitter" since the transmission
probability of a suitably prepared high energy wave packet is 25%. The high
frequency dependence of the cross section is w^{-4/3}. However, smooth
geometries arbitrarily close to the singular one require a finite amount of
negative energy matter. The negative-mass Schwarzschild has a qualitatively
different resolution interpreted to be fully reflecting. These 4d results are
similar to the 2d black hole and are generalized to an arbitrary dimension d>4.Comment: 47 pages, 5 figures. v2: See end of introduction for an important
note adde
Spin caloritronics in a CrBr-based magnetic van der Waals heterostructure
The recently reported magnetic ordering in insulating two-dimensional (2D)
materials, such as chromium triiodide (CrI) and chromium tribromide
(CrBr), opens new possibilities for the fabrication of magneto-electronic
devices based on 2D systems. Inevitably, the magnetization and spin dynamics in
2D magnets are strongly linked to Joule heating. Therefore, understanding the
coupling between spin, charge and heat, i.e. spin caloritronic effects, is
crucial. However, spin caloritronics in 2D ferromagnets remains mostly
unexplored, due to their instability in air. Here we develop a fabrication
method that integrates spin-active contacts with 2D magnets through hBN
encapsulation, allowing us to explore the spin caloritronic effects in these
materials. The angular dependence of the thermal spin signal of the CrBr/Pt
system is studied, for different conditions of magnetic field and heating
current. We highlight the presence of a significant magnetic proximity effect
from CrBr on Pt revealed by an anomalous Nernst effect in Pt, and suggest
the contribution of the spin Seebeck effect from CrBr. These results pave
the way for future magnonic devices using air-sensitive 2D magnetic insulators
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