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1.
M. Hohl J. Roth H.-R. Trebin 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):595-601
The icosahedral or decagonal symmetry of quasicrystals is well described by a periodic structure in higher dimensions. One
consequence is the existence of dynamic phason modes in addition to the phonon modes. In an atomistic model phasons show up
as correlated atomic jumps. We detect the phasons by the calculation of correlation functions and the dynamical structure
factor in molecular dynamics simulations similar to the procedure used for phonons. In the simulations it is also possible
to observe atomic jump processes directly. The models studied here represent icosahedral AlCuLi and decagonal AlCuCo quasicrystals.
Ring processes are observed in the icosahedral case, and flips in the decagonal model.
Received 17 March 2000 and Received in final form 8 June 2000 相似文献
2.
It has recently been claimed that the dynamics
of long-wavelength phason fluctuations has been observed in
i-AlPdMn quasicrystals [S. Francoual et al.
Phys. Rev. Lett. 91, 225501 (2003);
A. Létoublon et al. 54, 753 (2001)]. We will show that
the data reported call for a more detailed development of
the elasticity theory of Jarić and Nelsson [M.V. Jarić and D.R. Nelsson, Phys. Rev. B 37,
4458 (1988)]
in order to determine the nature of small phonon-like atomic displacements
with a symmetry that follows the phason elastic constants.
We also show that a simple model with a single diffusing tile is sufficient
to produce a signal that (1) is situated at a “satellite position”
at a distance q from each Bragg peak; that (2) has an intensity that
scales with the intensity of the corresponding Bragg peak;
(3) falls off as 1/q2; and (4) has a time decay constant that is proportional to 1/Dq2.
It is thus superfluous to call for a picture of “phason waves” in order to explain such data, especially as such “waves” violate
many physical principles. 相似文献
3.
O.J. Zogal P. Vajda F. Beuneu A. Pietraszko 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):451-456
AlH3 powder was bombarded with energetic electrons at 20 K and at room temperature and investigated by EPR, NMR, X-ray diffractometry,
and microwave dielectric-constant measurements. The EPR spectra of the irradiated powder and of a selected single crystal
cuboid of mm edge show a complex asymmetric line centered at g
= 2.009, with a Curie-like temperature dependence, attributed to radiation-induced color centers and/or their agglomerates. At the
same time, the grains, which have become shiny black after irradiation, exhibit an increase of both the real and the imaginary
part of . 27Al-NMR spectra of the irradiated powder present a Knight-shifted line at 1600(50) ppm, close to the position of bulk metallic
Al, and corresponding to a concentration of c(Al) . In addition, the main hydride line differs from that before irradiation, demonstrating an alteration of environmental symmetry.
The irradiation induces also a change in shape and width of the 1H-NMR line, another indication of symmetry change in the lattice. Finally, a refined X-ray single-crystal structure analysis
of the irradiated cuboid indicates a change of structure from trigonal R
-3
c to R
-3, with a loss of mirror symmetry for the two Al sites caused by the introduction of Al-defects in the vicinity of one of them.
Received: 20 October 1997 / Revised: 24 December 1997 / Accepted: 30 January 1998 相似文献
4.
V.V. Harutunyan V.A. Gevorkyan V.N. Makhov 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):35-38
The luminescence spectra of corundum monocrystals grown by different methods are investigated by means of a time-resolved
spectroscopy method at temperatures 90 K and 300 K. The existence of fast and slow emission in the VUV luminescence spectra
of irradiated and nonirradiated crystals was observed. We observed luminescence bands with a maximum at 326 nm produced by
F
+
centers. A new type of fast luminescence at the band of 270 nm was found. This is known as cross-luminescence and is connected
with the recombination of valence band electrons with the holes in the low ground band. It was shown that the band of 410
nm isn't due to to anionic centers (F-centers), but is determined by the short lifetime center of emission (F
-
-centers).
Received 20 October 1998 and Received in final form 20 January 1999 相似文献
5.
Summary Samples of Nasicon compounds (Na super ionic conductor) with different silicon and phosphorus contents were investigated by
performing radioluminescence experiments. In all samples examined, the Frenkel pairs, originated by the displacements of sodium
ions in lacunar sites, were found to be the dominant defects. Some useful information on sodium ion mobility was obtained
from the analysis of radioluminescence spectra. 相似文献
6.
G. Baldacchini R.M. Montereali T. Tsuboi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):261-264
In colored LiF crystals there are many absorption and emission bands which cover a wide region of the spectrum from 200 up
to 1 300 nm without breaking the continuity. In the frame of these favourable conditions we have performed some experiments
of energy transfer among various color centers. The results indicate the existence of efficient exchanges of radiative energy
among several bands by using only one exciting wavelength. In particular, the emissions of the F3
- and F2
- color centers centered at 900 and 1 100 nm, respectively, have been observed by pumping at 672 nm completely outside their
absorption bands.
Received 25 June 2001 and Received in final form 16 July 2001 相似文献
7.
M. Kaisermayr B. Sepiol H. Thiess G. Vogl E.E. Alp W. Sturhahn 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):335-341
Time-domain interferometry of synchrotron radiation (TDI) has recently been used as a tool for investigating diffusion in
glasses. This work deals with an extension of this technique to ordered structures. In a TDI experiment performed on the B2 alloy CoGa at the APS the intensity scattered into Bragg directions showed no detectable quasielastic signal. Experimental
lower limits of the elastic contribution are given. They are in accordance with the coherent scattering function derived in
this paper. This result indicates that TDI can be applied to diffusion in crystalline solids, e.g. intermetallic alloys, by using diffuse scattering. Requirements and limitations of diffuse scattering experiments are discussed.
Received 21 September 2000 and Received in final form 13 December 2000 相似文献
8.
9.
G. Durand F. Spiegelman A. R. Allouche 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):19-22
Recently, electric susceptibilities of
NanFn-1 clusters
have been measured by deflecting a molecular beam in an
inhomogeneous electric field. The analysis of the deflection of
a cluster by the electric field needs the calculation of the
electric properties. We present the calculation of the static
anisotropic and average dipolar polarizabilities within a model
in which the
NanFn-1 clusters (
2
n
23)
are treated as one electron embedded in the field of
n ions
Na+ and of n
- 1
ions F-. The accuracy of the results
is evaluated and discussed on small clusters (n
5)
in comparison with ab initio
calculations. The relationship between the polarizabilities, the
electronic localization and the geometric structure is
discussed. Received 10 September 2002 Published online 3 July
2003 相似文献
10.
M. Ricker J. Bachteler H.-R. Trebin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):351-363
In quasicrystals, there are not only conventional, but also phason displacement fields and associated Burgers vectors. We
have calculated approximate solutions for the elastic fields induced by two-, three- and fivefold straight screw- and edge-dislocations
in infinite icosahedral quasicrystals by means of a generalized perturbation method. Starting from the solution for elastic
isotropy in phonon and phason spaces, corrections of higher order reflect the two-, three- and fivefold symmetry of the elastic
fields surrounding screw dislocations. The fields of special edge dislocations display characteristic symmetries also, which
can be seen from the contributions of all orders.
Received 21 February 2001 and Received in final form 27 June 2001 相似文献
11.
12.
C. Wang C. Y. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):243-247
An ideal single vacancy can be formed by removing one carbon atom
from a hexagonal network. The vacancy is one of the most important
defect structures in carbon nanotubes (CNTs). Vacancies can
affect the mechanical, chemical, and electronic properties of CNTs.
We have systematically investigated single vacancies and their
related point defects for achiral, single-walled carbon nanotubes
(SWNTs) using first-principles calculations. The structures around
single vacancies undergo reconstruction without constraint, forming ground-stateor metastable-state structures. The 5-1DB
and 3DB point defects can be
formed in armchair CNTS, while the 5-1DB-P and 5-1DB-T point defects can be
formed in zigzag CNTs. The related point defects can transform into
each other under certain conditions. The formation energies of
armchair CNTs change smoothly with the tube radius, while in the
case of the 3DB defect, as the radius get larger, the formation energies
tend towards a constant value. 相似文献
13.
A. Aird E.K.H. Salje 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):205-210
A possible new high temperature superconducting phase was recently reported in WO
3
:Na. We have examined the reaction between sodium vapour and WO
3
, and compared the phases formed by the reaction to previously known WO
3
phases. By using light microscopy and electron microprobe analysis, domain walls from the interior of the crystal are shown
to have a much higher Na content than bulk material after reaction with Na vapour. This indicates preferential transport along
the domain walls. The result is very similar to a reduction reaction of WO
3
crystals in which twin walls lose oxygen preferentially. Oxygen deficient twin walls are superconducting with .
Received 3 September 1999 and Received in final form 15 December 1999 相似文献
14.
E.M. Alcalá E. López C. Aroca M.C. Sánchez P. Sánchez 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):473-476
We have studied the effect of the homogeneity of hydrogen distribution on magnetic properties of hydrogen charged amorphous
samples (Metglass 2826MB: Fe40Ni40Mo4B18). The results suggest that, in high magnetostrictive samples, the induced internal stresses and hence the magnetic anisotropy
are related to the hydrogen distribution and not to the total quantity of hydrogen inside the sample. To perform this study,
the homogeneity of hydrogen distribution in the sample was improved by using a very low rate of hydrogen charging by means
of a pulsed electrolytic current. Furthermore, this pulsed electrolytic current allows us to introduce a high quantity of
hydrogen without breaking the sample.
Received 7 May 1999 and Received in final form 11 October 1999 相似文献
15.
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
16.
E. Puchkaryov K. Maki 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):191-194
As is well known, Zn-substitution of Cu in the Cu-O2 plane in the hole-doped high Tc cuprates provides a semi-quantitative test of underlying d-wave superconductivity. Here we complement this with a parallel
study of Ni-substitution, which gives rise to weak scattering described with the Born approximation.
Received: 7 November 1997 / Revised: 14 November 1997 / Accepted: 24 November 1997 相似文献
17.
M. Potthoff W. Nolting 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):555-568
The correlation-driven transition from a paramagnetic metal to a paramagnetic Mott-Hubbard insulator is studied within the
half-filled Hubbard model for a thin-film geometry. We consider simple-cubic films with different low-index surfaces and film
thickness d ranging from d=1 (two-dimensional) up to d=8. Using the dynamical mean-field theory, the lattice (film) problem is self-consistently mapped onto a set of d single-impurity Anderson models which are indirectly coupled via the respective baths of conduction electrons. The impurity models are solved at zero temperature using the exact-diagonalization
algorithm. We investigate the layer and thickness dependence of the electronic structure in the low-energy regime. Effects
due to the finite film thickness are found to be the more pronounced the lower is the film-surface coordination number. For
the comparatively open sc(111) geometry we find a strong layer dependence of the quasi-particle weight while it is much less
pronounced for the sc(110) and the sc(100) film geometries. For a given geometry and thickness d there is a unique critical interaction strength U
c2
(d) at which all effective masses diverge and there is a unique strength U
c1
(d) where the insulating solution disappears. U
c2
(d) and U
c1
(d) gradually increase with increasing thickness eventually approaching their bulk values. A simple analytical argument explains
the complete geometry and thickness dependence of Uc2. Uc1 is found to scale linearly with Uc2.
Received 19 August 1998 相似文献
18.
M. Brunner F.F. Assaad A. Muramatsu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):209-212
We present a new finite-temperature quantum Monte Carlo algorithm to compute imaginary-time Green functions for a single hole
in the t-J model on non-frustrated lattices. Spectral functions are obtained with the Maximum Entropy method. Simulations of the one-dimensional
case show that a simple charge-spin separation Ansatz is able to describe the overall features of the spectral function such as the bandwidth and the compact support of the spectral function, over the whole energy range for values of J
/
t from 1/3 to 4. This is contrasted with the two-dimensional case. The quasiparticle weight Zk is computed on lattices up to L
=128 sites in one dimension, and scales as .
Received 15 February 2000 相似文献
19.
L. Benfatto A. Perali C. Castellani M. Grilli 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):609-612
We evaluate the charge and spin susceptibilities of the 2D attractive Hubbard model and we compare our results with Monte
Carlo simulations on the same model. We discuss the possibility to include topological Kosterlitz-Thouless superconducting
fluctuations in a standard perturbative approach substituting in the fluctuation propagator the Ginzburg-Landau correlation
length with the Kosterlitz-Thouless correlation length.
Received 30 June 1999 相似文献