3,820 research outputs found
Scaling properties of step bunches induced by sublimation and related mechanisms: A unified perspective
This work provides a ground for a quantitative interpretation of experiments
on step bunching during sublimation of crystals with a pronounced
Ehrlich-Schwoebel (ES) barrier in the regime of weak desorption. A strong step
bunching instability takes place when the kinetic length is larger than the
average distance between the steps on the vicinal surface. In the opposite
limit the instability is weak and step bunching can occur only when the
magnitude of step-step repulsion is small. The central result are power law
relations of the between the width, the height, and the minimum interstep
distance of a bunch. These relations are obtained from a continuum evolution
equation for the surface profile, which is derived from the discrete step
dynamical equations for. The analysis of the continuum equation reveals the
existence of two types of stationary bunch profiles with different scaling
properties. Through a mathematical equivalence on the level of the discrete
step equations as well as on the continuum level, our results carry over to the
problems of step bunching induced by growth with a strong inverse ES effect,
and by electromigration in the attachment/detachment limited regime. Thus our
work provides support for the existence of universality classes of step
bunching instabilities [A. Pimpinelli et al., Phys. Rev. Lett. 88, 206103
(2002)], but some aspects of the universality scenario need to be revised.Comment: 21 pages, 8 figure
Magnetic coupling in highly-ordered NiO/Fe3O4(110): Ultrasharp magnetic interfaces vs. long-range magnetoelastic interactions
We present a laterally resolved X-ray magnetic dichroism study of the
magnetic proximity effect in a highly ordered oxide system, i.e. NiO films on
Fe3O4(110). We found that the magnetic interface shows an ultrasharp
electronic, magnetic and structural transition from the ferrimagnet to the
antiferromagnet. The monolayer which forms the interface reconstructs to
NiFe2O4 and exhibits an enhanced Fe and Ni orbital moment, possibly caused by
bonding anisotropy or electronic interaction between Fe and Ni cations. The
absence of spin-flop coupling for this crystallographic orientation can be
explained by a structurally uncompensated interface and additional
magnetoelastic effects
Records and sequences of records from random variables with a linear trend
We consider records and sequences of records drawn from discrete time series
of the form , where the are independent and identically
distributed random variables and is a constant drift. For very small and
very large drift velocities, we investigate the asymptotic behavior of the
probability of a record occurring in the th step and the
probability that all entries are records, i.e. that . Our work is motivated by the analysis of temperature time series in
climatology, and by the study of mutational pathways in evolutionary biology.Comment: 21 pages, 7 figure
Persistence exponents for fluctuating interfaces
Numerical and analytic results for the exponent \theta describing the decay
of the first return probability of an interface to its initial height are
obtained for a large class of linear Langevin equations. The models are
parametrized by the dynamic roughness exponent \beta, with 0 < \beta < 1; for
\beta = 1/2 the time evolution is Markovian. Using simulations of
solid-on-solid models, of the discretized continuum equations as well as of the
associated zero-dimensional stationary Gaussian process, we address two
problems: The return of an initially flat interface, and the return to an
initial state with fully developed steady state roughness. The two problems are
shown to be governed by different exponents. For the steady state case we point
out the equivalence to fractional Brownian motion, which has a return exponent
\theta_S = 1 - \beta. The exponent \theta_0 for the flat initial condition
appears to be nontrivial. We prove that \theta_0 \to \infty for \beta \to 0,
\theta_0 \geq \theta_S for \beta
1/2, and calculate \theta_{0,S} perturbatively to first order in an expansion
around the Markovian case \beta = 1/2. Using the exact result \theta_S = 1 -
\beta, accurate upper and lower bounds on \theta_0 can be derived which show,
in particular, that \theta_0 \geq (1 - \beta)^2/\beta for small \beta.Comment: 12 pages, REVTEX, 6 Postscript figures, needs multicol.sty and
epsf.st
R-matrix theory of driven electromagnetic cavities
Resonances of cylindrical symmetric microwave cavities are analyzed in
R-matrix theory which transforms the input channel conditions to the output
channels. Single and interfering double resonances are studied and compared
with experimental results, obtained with superconducting microwave cavities.
Because of the equivalence of the two-dimensional Helmholtz and the stationary
Schroedinger equations, the results present insight into the resonance
structure of regular and chaotic quantum billiards.Comment: Revtex 4.
Residual Symmetries in the Spectrum of Periodically Driven Alkali Rydberg States
We identify a fundamental structure in the spectrum of microwave driven
alkali Rydberg states, which highlights the remnants of the Coulomb symmetry in
the presence of a non-hydrogenic core. Core-induced corrections with respect to
the hydrogen spectrum can be accounted for by a perturbative approach.Comment: 7 pages, 2 figures, to be published in Europhysics Letter
Absence of non-trivial asymptotic scaling in the Kashchiev model of polynuclear growth
In this brief comment we show that, contrary to previous claims [Bartelt M C
and Evans J W 1993 {\it J.\ Phys.\ A} 2743], the asymptotic
behaviour of the Kashchiev model of polynuclear growth is trivial in all
spatial dimensions, and therefore lies outside the Kardar-Parisi-Zhang
universality class.Comment: 3 pages, 4 postscript figures, uses eps
Sample-Dependent Phase Transitions in Disordered Exclusion Models
We give numerical evidence that the location of the first order phase
transition between the low and the high density phases of the one dimensional
asymmetric simple exclusion process with open boundaries becomes sample
dependent when quenched disorder is introduced for the hopping rates.Comment: accepted in Europhysics Letter
A pseudo-spectral approach to inverse problems in interface dynamics
An improved scheme for computing coupling parameters of the
Kardar-Parisi-Zhang equation from a collection of successive interface
profiles, is presented. The approach hinges on a spectral representation of
this equation. An appropriate discretization based on a Fourier representation,
is discussed as a by-product of the above scheme. Our method is first tested on
profiles generated by a one-dimensional Kardar-Parisi-Zhang equation where it
is shown to reproduce the input parameters very accurately. When applied to
microscopic models of growth, it provides the values of the coupling parameters
associated with the corresponding continuum equations. This technique favorably
compares with previous methods based on real space schemes.Comment: 12 pages, 9 figures, revtex 3.0 with epsf style, to appear in Phys.
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