共查询到20条相似文献,搜索用时 15 毫秒
1.
M. Pinterić T. Vuletić M. Lončarić S. Tomić J.U. von Schütz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):487-493
We report a detailed characterization of an unique 3-fold commensurate insulating state in single crystals of the organic
– inorganic d hybrid Cu(DMe-DCNQI)2 systems with deuterated and partially deuterated DCNQI ring, by means of low-frequency dielectric spectroscopy. A broad relaxation
mode of strength centred at kHz is observed in the hysteresis temperature region in which the insulating phase coexists with metallic islands. At lower
temperatures, outside the nucleation range, the relaxation narrows, approaching a Debye-like form for an overdamped response
of a system with a single degree of freedom. Both, the relaxation strength and the mean relaxation time () are much larger than that expected for single-particle excitations. These features suggest the origin of the dielectric
relaxation as an intrinsic property of the N = 3 charge density wave state.
Received 1 December 1999 and Received in final form 5 April 2000 相似文献
2.
P. Jensen N. Combe H. Larralde J. L. Barrat C. Misbah A. Pimpinelli 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):497-504
We study the relaxation to equilibrium of two dimensional islands containing up to 20 000 atoms by Kinetic Monte Carlo simulations.
We find that the commonly assumed relaxation mechanism - curvature-driven relaxation via atom diffusion - cannot explain the results obtained at low temperatures, where the island edges consist in large facets.
Specifically, our simulations show that the exponent characterizing the dependence of the equilibration time on the island
size is different at high and low temperatures, in contradiction with the above cited assumptions. Instead, we propose that
- at low temperatures - the relaxation is limited by the nucleation of new atomic rows on the large facets: this allows us
to explain both the activation energy and the island size dependence of the equilibration time.
Received 7 December 1998 and Received in final form 18 March 1999 相似文献
3.
P.L. Krapivsky J.F.F. Mendes S. Redner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):401-404
We investigate submonolayer epitaxial growth with a fixed monomer flux and irreversible aggregation of adatom islands due
to an effective island diffusion, with a diffusivity for an mass k island proportional to . For , there is a steady state, while for , continuously evolving logarithmic islanding occurs in which the island density grows extremely slowly, as . In the latter regime, the island size distribution exhibits complex, but universal, multiple-scale mass dependence which
we account for theoretically.
Received: 3 June 1998 / Accepted: 13 July 1998 相似文献
4.
A kinetic Monte Carlo investigation of island nucleation and growth in thin-film epitaxy in the presence of substrate-mediated interactions 总被引:3,自引:0,他引:3
K.A. Fichthorn M.L. Merrick M. Scheffler 《Applied Physics A: Materials Science & Processing》2002,75(1):17-23
Island nucleation and growth during thin-film epitaxy is typically described using mean-field rate equations, which can be
solved to predict the density of stable islands as a function of the deposition rate and the diffusivity of an isolated adatom.
Recent theoretical and experimental studies indicate that medium- and long-range interactions between adatoms may change the
simple picture that nucleation theory provides, because the presence of these interactions invalidates some of its assumptions.
In this work, we investigate the ramifications of medium-range, substrate-mediated interactions for aspects of island nucleation
and growth. The interactions are quantified for Ag on a strained Ag (111) substrate using density-functional-theory calculations.
We discuss our incorporation of these interactions into a kinetic Monte Carlo model to study thin-film epitaxy. The simulated
thin-film growth is compared to predictions by standard nucleation theory. We discuss features of island nucleation and growth
that are actuated by the presence of medium-range interactions.
Received: 30 April 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002 相似文献
5.
A nonmean-field model for the ripening of two-dimensional islands is presented. In this model, the adatom sea is divided into many small cells that are the polygons of a Voronoi network. The chemical potentials of adatom seas surrounding different islands are different. Strain generated by lattice mismatch is introduced into the model.Computer simulation under periodic boundary conditions is carried out to describe the island ripening in two cases (with and without strain), and demonstrates that small islands may grow faster than large islands, which cannot occur in the mean-field model. The simulated results also show that including strain will slow down the evolution of average island size, and an explanation for this is given. 相似文献
6.
T. Müller W. Selke 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):549-553
Using kinetic Monte Carlo simulations and a bond-counting ansatz, thermal stability and diffusion of an adatom island on a
crystal surface are studied. At low temperatures, the diffusion constant D is found to decrease for a wide range of island sizes like , where is close to one, N being the number of adatoms in the cluster. By heating up the surface, the system undergoes a phase transition above which
the island disappears. Characteristics of that transition are discussed.
Received 20 January 1999 相似文献
7.
Using a slightly simplified version of the integrate and fire model of a neural network with delay, I study the stability
of the phase-locked state dependent on the coupling between the neurons and especially on a delay time. The coupling between
neurons may be arbitrary. It is shown that the phase-locked state becomes less stable with increasing delay and that relaxation
oscillations occur.
Received 28 December 1999 and Received in final form 13 June 2000 相似文献
8.
D.H. Zanette 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):537-541
A system of globally coupled maps whose synchronized dynamics differs from the individual (chaotic) evolution is considered.
For nonchaotic synchronized dynamics, the synchronized state becomes stable at a critical coupling intensity lower than that
of the fully chaotic case. Below such critical point, synchronization is also stable in a set of finite intervals. Moreover,
the system is shown to exhibit multistability, so that even when the synchronized state is stable not all the initial conditions
lead to synchronization of the ensemble.
Received 22 October 1999 相似文献
9.
J.P. Zagorodny Y. Gaididei F.G. Mertens A.R. Bishop 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):471-487
We investigate the dynamics of out-of-plane (OP) vortices, in a 2-dimensional (2D) classical Heisenberg magnet with a weak
anisotropy in the coupling of z-components of spins (easy plane anisotropy), on square lattices, under the influence of a rotating in-plane (IP) magnetic
field. Switching of the z-component of magnetization of the vortex is studied in computer simulations as a function of the magnetic field's amplitude
and frequency. The effects of the size and the anisotropy of the system on the switching process are shown. An approximate
dynamical equivalence of the system, in the bulk limit, to another system with both IP and OP static fields in the rotating reference frame is demonstrated, and qualitatively the same switching and critical behavior is obtained
in computer simulations for both systems. We briefly discuss the interplay between finite size effects (image vortices) and
the applied field in the dynamics of OP vortices. In the framework of a discrete reduced model of the vortex core we propose a mechanism for switching the vortex polarization, which can account qualitatively
for all our results. A coupling between the IP movement (trajectories) of the vortex center and the OP core structure oscillations,
due to the discreteness of the underlying lattice, is shown. A connection between this coupling and our reduced model is made
clear, through an analogy with a generalized Thiele equation.
Received 6 June 2002 / Received in final form 4 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: juan.zagorodny@uni-bayreuth.de 相似文献
10.
11.
P. Thalmeier A.N. Yaresko 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):495-508
An investigation of the spin excitation spectrum of charge ordered (CO) NaV2O5 is presented. We discuss several different exchange models which may be relevant for this compound, namely in-line and zig-zag
chain models with weak as well as strong inter-chain coupling and also a ladder model and a CO/MV (mixed valent) model. We
put special emphasis on the importance of large additional exchange across the diagonals of V-ladders and the presence of
exchange anisotropies on the excitation spectrum. It is shown that the observed splitting of transverse dispersion branches
may both be interpreted as anisotropy effect as well as acoustic-optic mode splitting in the weakly coupled chain models.
In addition we calculate the field dependence of excitation modes in these models. Furthermore we show that for strong inter-chain
coupling, as suggested by recent LDA + U results, an additional high energy optical excitation appears and the spin gap is
determined by anisotropies. The most promising CO/MV model predicts a spin wave dispersion perpendicular to the chains which
agrees very well with recent results obtained by inelastic neutron scattering.
Received 30 April 1999 and Received in final form 5 October 1999 相似文献
12.
H. Willaime J. Maurer F. Moisy P. Tabeling 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):363-369
Turbulence produced in low temperature helium gas flowing over arrays of rectangular- and triangular-shaped blunt obstacles
is investigated experimentally. The set-up allows both low fluctuation rates (down to 8%), and high microscale Reynolds numbers,
(up to 1 150). The forced Kolmogorov equation is found to apply accurately. Similar to another flow configuration (counter
rotating flow case [1]), the analysis of the flatness factor evolution with the Reynolds number reveals a transitional behavior
around 650.
Received 26 August 1999 and Received in final form 28 August 2000 相似文献
13.
K. Dworecki T. Kosztolowicz St. Mrówczynski S. Wasik 《The European physical journal. E, Soft matter》2000,3(4):389-394
The near membrane layer is a region where the concentration of the substance transported across the membrane is significantly
decreased. Its thickness is defined as a length over which the concentration drops k times with k being an arbitrary large number. The time evolution of such a layer is studied experimentally by means of the laser interferometric
method. It is shown that within the experimental errors the thickness of the near membrane layer grows in time for any k as with the coefficient a being independent of the initial concentration and the membrane permeability. Time evolution of the near membrane layers
is also analyzed theoretically. The regularities found experimentally are naturally described within the model which has been
earlier developed by one of us. In particular, a scales as .
Received 12 November 1999 and Received in final form 3 July 2000 相似文献
14.
H. Kallabis P.L. Krapivsky D.E. Wolf 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):801-804
The typical island distance in submonolayer epitaxial growth depends on the growth conditions via an exponent . This exponent is known to depend on the substrate dimensionality, the dimension of the islands, and the size i* of the critical nucleus for island formation. In this paper we study the dependence of on i* in one-dimensional epitaxial growth. We derive that for and confirm this result by computer simulations.
Received: 26 May 1998 / Accepted: 23 June 1998 相似文献
15.
M.-P. Gorza S. Saltiel H. Failache M. Ducloy 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):113-126
A theory of van der Waals (vdW) interaction between an atom (in ground or excited state) and a birefringent dielectric surface
with an arbitrary orientation of the principal optic axis (C-axis) is presented. Our theoretical approach is based on quantum-mechanical linear response theory, using generalized susceptibilities
for both atom and electromagnetic field. Resonant atom-surface coupling is predicted for excited-state atoms interacting with
a dispersive dielectric surface, when an atom de-excitation channel gets into resonance with a surface polariton mode. In
the non-retarded regime, this resonant coupling can lead to enhanced attractive or repulsive vdW surface forces, as well as
to a dissipative coupling increasing the excited-state relaxation. We show that the strongly non-scalar character of the interaction
with the birefringent surface produces a C-axis-dependent symmetry-breaking of the atomic wavefunction. Changes of the C-axis orientation may also lead to a frequency shift of the surface polariton mode, allowing for tuning on or off the resonant coupling, resulting in a special type of engineering of surface forces. This is analysed here in the case of
cesium 6D
3/2 level interacting with a sapphire interface, where it is shown that an adequate choice of the sapphire C-axis orientation allows one to transform vdW surface attraction into repulsion, and to interpret recent experimental observations
based on selective reflection methods [H. Failache etal., Phys. Rev. Lett. 83, 5467 (1999)].
Received 24 January 2001 相似文献
16.
F.W.S. Lima J.E. Moreira J.S. Andrade Jr. U.M.S. Costa 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):107-110
We investigate the two-dimensional eight-states ferromagnetic Potts model in the Voronoi-Delaunay tessellation. In this study,
we assume that the coupling factor J varies with the distance r between the first neighbors as , with . The disordered system is simulated applying the single-cluster Monte-Carlo update algorithm and the reweighting technique.
We find that this model displays a first-order phase transition if , in agreement with previous recent studies. For and 1.0, a typical second order transition is observed and the critical exponents for magnetization and susceptibility are
calculated.
Received 19 May 1999 and Received in final form 2 June 1999 相似文献
17.
K. Morgenstern E. Laegsgaard I. Stensgaard F. Besenbacher M. Böhringer W.-D. Schneider R. Berndt F. Mauri A. De Vita R. Car 《Applied Physics A: Materials Science & Processing》1999,69(5):559-569
We investigate atomic and molecular nanostructures on metal surfaces by variable low-temperature scanning tunnelling microscopy.
In combination with molecular dynamics calculations we achieve a detailed understanding of the stability of these structures.?Atomic
nanostructures in homoepitaxial metallic systems are thermodynamically only metastable. Two-dimensional islands on Ag(110)
decay above a threshold temperature of T
l=175 K. Caused by the anisotropy of the surface, distinct decay behaviours exist above and below a critical temperature of
T
c=220 K. Calculations based on effective medium potentials of the underlying rate limiting atomic processes allow us to identify
the one-dimensional decay below T
c as well as the two-dimensional decay above T
c.?In contrast to atoms, the intermolecular electrostatic interaction of polar molecules leads to thermodynamically stable
structures. On the reconstructed Au(111) surface, the pseudo-chiral 1-nitronaphthalin forms two-dimensional supermolecular
clusters consisting predominantly of ten molecules. Comparison of images with submolecular resolution to local density calculations
elucidates the thermodynamical stability as well as the internal structure of the decamers.
Received: 25 March 1999 / Accepted: 17 August 1999 / Published online: 6 October 1999 相似文献
18.
A.E. Allahverdyan Th.M. Nieuwenhuizen D.B. Saakian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):317-335
In a p-spin interaction spherical spin-glass model both the spins and the couplings are allowed to change with time. The spins are
coupled to a heat bath with temperature T, while the coupling constants are coupled to a bath having temperature TJ. In an adiabatic limit (where relaxation time of the couplings is much larger that of the spins) we construct a generalized
two-temperature thermodynamics. It involves entropies of the spins and the coupling constants. The application for spin-glass
systems leads to a standard replica theory with a non-vanishing number of replicas, n=T/T
J
. For p>2 there occur at low temperatures two different glassy phases, depending on the value of n. The obtained first-order transitions have positive latent heat, and positive discontinuity of the total entropy. This is
an essentially non-equilibrium effect. The dynamical phase transition exists only for n<1. For p=2 correlation of the disorder (leading to a non-zero n) removes the known marginal stability of the spin glass phase. If the observation time is very large there occurs no finite-temperature
spin glass phase. In this case there are analogies with the non-equilibrium (aging) dynamics. A generalized fluctuation-dissipation
relation is derived.
Received 12 July 1999 and Received in final form 8 December 1999 相似文献
19.
D.C. Cabra A. Honecker P. Pujol 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):55-73
We analyze the phase diagram of a system of spin-1/2 Heisenberg antiferromagnetic chains interacting through a zig-zag coupling,
also called zig-zag ladders. Using bosonization techniques we study how a spin-gap or more generally plateaux in magnetization
curves arise in different situations. While for coupled XXZchains, one has to deal with a recently discovered chiral perturbation, the coupling term which is present for normal ladders
is restored by an external magnetic field, dimerization or the presence of charge carriers. We then proceed with a numerical
investigation of the phase diagram of two coupled Heisenberg chains in the presence of a magnetic field. Unusual behaviour
is found for ferromagnetic coupled antiferromagnetic chains. Finally, for three (and more) legs one can choose different inequivalent
types of coupling between the chains. We find that the three-leg ladder can exhibit a spin-gap and/or non-trivial plateaux
in the magnetization curve whose appearance strongly depends on the choice of coupling.
Received 11 February 1999 and Received in final form 16 June 1999 相似文献
20.
G. Jin J.L. Liu S.G. Thomas Y.H. Luo K.L. Wang B.-Y. Nguyen 《Applied Physics A: Materials Science & Processing》2000,70(5):551-554
Self-organized Ge islands grown on patterned Si(001) substrates have been investigated. Selective epitaxial growth (SEG) of
Si is carried out with gas-source molecular beam epitaxy to form Si stripe mesas followed by subsequent Ge island growth.
Self-aligned Ge islands with regular spacing are formed on the <110>-oriented ridges of the Si mesas. The regular spacing
is driven by the repulsive interaction between the neighbor islands through the substrates. A mono-modal distribution of the
islands has been observed on the ridges of the Si mesas. The spatial confinement as well as the preferential nucleation is
believed to be the mechanism of this alignment of the self-organized Ge islands.
Received: 16 July 1999 / Accepted: 6 August 1999 / Published online: 24 March 2000 相似文献