共查询到20条相似文献,搜索用时 562 毫秒
1.
E.B. Lopes H. Alves E. Ribera M. Mas-Torrent P. Auban-Senzier E. Canadell R.T. Henriques M. Almeida E. Molins J. Veciana C. Rovira D. Jérome 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):27-33
This article reports the investigation of a new low-dimensional organic salt, (TTDM-TTF)2 [Au(mnt)2], by single crystal X-ray diffraction, static magnetic susceptibility, EPR, thermopower, electrical resistivity measurements
under pressure up to 25 kbar and band structure calculations. The crystal structure consists in a dimerized head to tail stacking
of TTDM-TTF molecules separated by layers of orthogonal Au(mnt)2 anions. The absence of overlap between neighboring chains coming from this particular crystal structure leads to an extreme
one-dimensionality (1-D) for which the carriers of the half-filled conduction band become strongly localized in a Mott-Hubbard
insulating state. This material is the first 1-D conductor in which the Mott-Hubbard insulating character cannot be suppressed
under pressure.
Received 15 April 2002 / Received in final form 17 June 2002 Published online 17 September 2002 相似文献
2.
R.K. Roy S.K. Mandal A.K. Pal 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):109-114
Nanocrystalline Au and Ag in multilayer thin film form with Au/Ag/Au structure were prepared by high pressure (∼40 Pa) d.c.
sputtering techniques. The Ag concentrations in AgxAu1-x films were changed from x = 0 to 1. These multilayer films with varying Ag concentration showed significant changes in microstructures obtained from
TEM and XRD analyses. The optical absorption spectra of these multilayer films showed a single plasmon band confirming the
formation of Au-Ag alloy. We ascribe this alloying to the interfacial reactions in nanophase limited at the Au-Ag interface.
The red-shift and broadening of the plasmon bands with the increase in silver concentration could be associated to the increase
in size of the nanoparticles and its distribution. The observed red shift in the plasmon band may be associated with the change
in electronic structure at the Au-Ag interface due to configuration mixing of the atomic energy levels of Au and Ag.
Received 17 October 2002 / Received in final form 26 February 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: msakp@mahendra.iacs.res.in 相似文献
3.
Lei Gao Yanyan Huang 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):165-171
The effective linear and nonlinear optical properties of metal/dielectric composite media, in which ellipsoidal metal inclusions
are distributed in shape, are investigated. The shape distribution function P(L
x, L
y) is assumed to be 2Δ-2θ(L
x - 1/3 + Δ/3)θ(L
y - 1/3 + Δ/3)θ(2/3 + Δ/3 - L
x - L
y), where θ( . . . ) is the Heaviside function, Δ is the shape variance and Li are the depolarization factors of the ellipsoidal inclusions along i-symmetric axes (i = x, y). Within the spectral representation, we adopt Maxwell-Garnett type approximation to study the effect of shape variance Δ
on the effective nonlinear optical properties. Numerical results show that both the effective linear optical absorption α
∼ ωIm() and the modulus of the effective third-order optical nonlinearity enhancement |χ(3)
e|/χ(3)
1 exhibit the nonmonotonic behavior with Δ. Moreover, with increasing Δ, the optical absorption and the nonlinearity enhancement
bands become broad, accompanied with the decrease of their peaks. The adjustment of Δ from 0 to 1 allows us to examine the
crossover behavior from no separation to large separation between optical absorption and nonlinearity enhancement peaks. As
Δ → 0, i.e., the ellipsoidal shape deviates slightly from the spherical one, the dependence of |χ(3)
e|/χ(3)
1 on Δ becomes strong first and then weak with increasing the imaginary part of inclusions' dielectric constant. In the dilute
limit, the exact formula for the effective optical nonlinearity is derived, and the present approximation characterizes the
exact results better than old mean field one does.
Received 10 December 2002 Published online 4 June 2003
RID="a"
ID="a"e-mail: lgaophys@pub.sz.jsinfo.net 相似文献
4.
H. Gayvallet J.-C. Géminard 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):369-375
We have studied the temperature dependent resistivity ρ(
T
) of La2-xSrxCuO4 epitaxial thin films in the doping range 0.045 ⩽
x
⩽ 0.25 in pulsed magnetic fields up to 50 T. The zero-field resistivity ρ(
T
) of these samples in the pseudogap regime, can be scaled onto one single universal curve in a broad temperature range by using
a linear transformation of both temperature and resistivity. The high field data ρ(
T
) reveal a metal to insulator transition (MIT) at low temperatures, well into the overdoped regime. For samples having k
F
l
< 1, with kF the Fermi wave vector and l the mean free path, this low temperature insulating behavior of the resistivity is described by the variable range hopping
conductivity (VRH). For samples with k
F
l
> 1, the divergence follows ρ(
T
) ∼
ln
(1/
T
) or a power law, depending upon the Sr-content. We further found that the residual conductivity at the minimum in ρ(
T
), appearing due to the MIT, follows a linear behavior with respect to the Sr-content. It is argued that the unusual MIT in
compounds with k
F
l
> 1, is most probably associated with the pseudogap and the behavior of charge stripes at low temperatures.
Received 4 January 2002 / Received in final form 7 May 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: liesbet.weckhuysen@fys.kuleuven.ac.be 相似文献
5.
G. Albinet J.M. Debierre P. Knauth C. Lambert L. Raymond 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):421-427
We describe a two-dimensional (2D) and a three-dimensional (3D) percolation model for ionic conductor-insulator composites
such as copper(I) bromide-titanium dioxide (CuBr-TiO2) or lithium iodide-alumina (LiI-Al2O3). These composites present an enhanced conductivity closely related to the insulator concentration. This effect is explained
by the formation of highly conducting space charge regions near the phase boundaries which are represented by good conductor
bonds. Our numerical model takes into account grain size and correlation effects. The dimension has a leading role for the
conduction properties. In the 2D case, the good conductor bonds do not percolate, whatever the insulator concentration, and
the maximum conductivity of the composite samples is of the same order as that of the ionic conductor grains. The behavior
of the system is very different in the 3D case where, for a large domain of composition, the good conductors percolate through
the regions between the conductor grains. For the CuBr-TiO2 composites the conductivity versus composition curve is bell-shaped. Conversely, in the LiI-Al2O3 system, a linear relation between the conductivity and the insulator volume fraction is obtained in the experiments. Our
model gives a plausible interpretation of the conductivity in both systems.
Received 10 April 2001 相似文献
6.
A. Urbina C. Díaz-Paniagua A.F. Braña F. Batallán 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):463-468
We present measurements of the diagonal Rxx and off-diagonal Rxy magnetoresistance under quantum Hall conditions on several high electron mobility transistors (HEMT) based on InxGa1-xAs quantum wells. From the magnetoresistance tensor we obtain the longitudinal conductivity σ
xx
. We study the transport mechanisms near the σ
xx
minima at temperatures ranging between 2 K and 35 K; activated transport is the dominant mechanism for temperatures above
7 K while variable range hopping conductivity is significant for lower temperatures. We show that electron-electron correlations
should be taken into account to explain the conductivity vs temperature behaviour below 5 K. Finally, we study the behaviour of the localization length as a function of Landau level
filling and obtain a critical exponent γ = 3.45±0.15.
Received 6 June 2001 and Received in final form 16 October 2001 相似文献
7.
E. Bogomolny U. Gerland C. Schmit 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):121-132
We propose a plasma model for spectral statistics displaying level repulsion without long-range spectral rigidity, i.e. statistics intermediate between random matrix and Poisson statistics similar to the ones found numerically at the critical
point of the Anderson metal-insulator transition in disordered systems and in certain dynamical systems. The model emerges
from Dysons one-dimensional gas corresponding to the eigenvalue distribution of the classical random matrix ensembles by restricting
the logarithmic pair interaction to a finite number k of nearest neighbors. We calculate analytically the spacing distributions and the two-level statistics. In particular we
show that the number variance has the asymptotic form Σ2(L) ∼χL for large L and the nearest-neighbor distribution decreases exponentially when s→∞, P(s) ∼ exp(- Λs) with Λ = 1/χ = kβ + 1, where β is the inverse temperature of the gas (β = 1, 2 and 4 for the orthogonal, unitary and symplectic symmetry class
respectively). In the simplest case of k = β = 1, the model leads to the so-called Semi-Poisson statistics characterized by particular simple correlation functions
e.g.
P(s) = 4s exp(- 2s). Furthermore we investigate the spectral statistics of several pseudointegrable quantum billiards numerically and compare
them to the Semi-Poisson statistics.
Received 13 September 2000 相似文献
8.
S. Dubois S. Harel M. Grosbras 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):507-510
Macroscopic resistivity measurements have been performed on TiC/Al2O3 random mixtures submitted to uniaxial compression (0-95 kN). Such a random mixture exhibits an insulator-conductor transition
which appears at increasing force while decreasing the conductive composition of the TiC/Al2O3 mixture. It is demonstrated that the conductivity behavior may be understood in the framework of a site percolation model.
Finally, the rate of creation of the contacts between conductive grains is extracted from the macroscopic resistivity measurements.
Received 6 December 2000 and Received in final form 30 March 2001 相似文献
9.
L. Raymond J.-M. Laugier S. Schäfer G. Albinet 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):355-364
Binary disordered systems are usually obtained by mixing two ingredients in variable proportions: conductor and insulator,
or conductor and super-conductor. They present very specific properties, in particular the second-order percolation phase
transition, with its fractal geometry and the multi-fractal properties of the current moments. These systems are naturally
modeled by regular bi-dimensional or tri-dimensional lattices, on which sites or bonds are chosen randomly with given probabilities.
The two significant parameters are the ratio h = σ
1/σ of the complex conductances, σ and σ
1, of the two components, and their relative abundances p (or, respectively, 1 - p). In this article, we calculate the impedance of the composite by two independent methods: the so-called spectral method,
which diagonalises Kirchhoff's Laws via a Green function formalism, and the Exact Numerical Renormalization method (ENR). These methods are applied to mixtures of
resistors and capacitors (R-C systems), simulating e.g. ionic conductor-insulator systems, and to composites constituted of resistive inductances and capacitors (LR-C systems),
representing metal inclusions in a dielectric bulk. The frequency dependent impedances of the latter composites present very
intricate structures in the vicinity of the percolation threshold. In this paper, we analyse the LR-C behavior of compounds
formed by the inclusion of small conducting clusters (“n-legged animals”) in a dielectric medium. We investigate in particular their absorption spectra who present a pattern of sharp
lines at very specific frequencies of the incident electromagnetic field, the goal being to identify the signature of each
animal. This enables us to make suggestions of how to build compounds with specific absorption or transmission properties
in a given frequency domain.
Received 16 August 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: laurent.raymond@l2mp.fr
RID="b"
ID="b"e-mail: steffen.schaefer@l2mp.fr
RID="c"
ID="c"UMR CNRS 6137 相似文献
10.
We consider a low-density assembly of spherical colloids, such that each is clothed by L end-grafted chemically incompatible polymer chains either of types A or B. These are assumed to be dissolved in a good common solvent. We assume that colloids are of small size to be considered as
star-polymers. Two adjacent star-polymers A and B interact through a force F originating from both excluded-volume effects and chemical mismatch between unlike monomers. Using a method developed by
Witten and Pincus (Macromolecules 19, 2509 (1986)) in the context of star-polymers of the same chemical nature, we determine exactly the force F as a function of the center-to-center distance h. We find that this force is the sum of two contributions F
e and F
s. The former, that results from the excluded volume, decays as F
e∼A
L
h
-1, with the L -dependent universal amplitude A
L∼L
3/2. While the second, which comes from the chemical mismatch, decays more slowly as F
s∼χB
L
h
-1 - τ, where τ is a critical exponent whose value is found to be τ 0.40, and χ is the standard Flory interaction parameter. We find that the corresponding L-dependent universal amplitude is B
L∼L
3 + τ
/2. Theses forces are comparable near the cores of two adjacent star-polymers, i.e. for h∼h
c∼a
(a is the monomer size). Finally, for two star-polymers of the same chemical nature (A or B), the force F that simply results from excluded-volume effects coincides exactly with F
e, and then the known result is recovered.
Received 2 October 2000 and Received in final form 24 January 2001 相似文献
11.
J. Ding L. Wang A. Roy J. Ghose 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):49-54
A compensation temperature of 138 K was observed in the temperature-dependent magnetization curves of MoFe2O4. Relatively slow magnetization relaxation characterized the transitions between different spin states (compensated and uncompensated).
Large magnetic after effect was found in time-dependent magnetization curves after heating or cooling from different characteristic
temperatures for different spin states. The magnetic relaxation was nearly independent on magnetic field, supporting the presence
of spin states and no involvement of domain structure. For the Ti substituted Mo0.6Ti0.4Fe2O4 sample, there were a compensation at ∼ 100 K and a maximum of magnetization at ∼ 175 K. Similar results of anomalous magnetic
relaxation was observed in Ti substituted Mo-ferrite (Mo0.6Ti0.4Fe2O4). If the Mo0.6Ti0.4Fe2O4 sample was heated from 100 K to 235 K, the time-dependent magnetization curve could be considered as a combination of two
magnetic relaxation processes. However, if the sample was heated from 100 K to 295 K, the time- dependent magnetization curve
became complex.
Received 30 October 2001 and Received in final form 21 January 2002 相似文献
12.
M.L. Ndawana R.A. Römer M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):399-407
We compute the number level variance Σ
2 and the level compressibility χ from high precision data for the Anderson model of localization and show that they can be
used in order to estimate the critical properties at the metal-insulator transition by means of finite-size scaling. With
N, W, and L denoting, respectively, linear system size, disorder strength, and the average number of levels in units of the mean level
spacing, we find that both χ(N, W) and the integrated Σ
2 obey finite-size scaling. The high precision data was obtained for an anisotropic three-dimensional Anderson model with disorder
given by a box distribution of width W/2. We compute the critical exponent as ν≈ 1.45±0.12 and the critical disorder as W
c≈ 8.59±0.05 in agreement with previous transfer-matrix studies in the anisotropic model. Furthermore, we find χ≈ 0.28±0.06
at the metal-insulator transition in very close agreement with previous results.
Received 1st November 2001 and Received in final form 8 March 2002 Published online 6 June 2002 相似文献
13.
J. Blasco J. García M.C. Sánchez J. Campo G. Subías J. Pérez-Cacho 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):469-479
Magnetic measurements have been carried out in different LaNi1-xMnxO
3 + δ
samples with 0.1 ⩽
x
⩽ 0.9. All these samples show two magnetic anomalies, one at relatively high temperature characteristic of a ferromagnetic ordering
and the other at low temperature, typical of magnetic relaxation phenomena. Neutron diffraction patterns indicate that long-range
ferromagnetic ordering is only achieved for x
≥ 0.5. Neutron patterns of LaNi0.5Mn0.5O
3 + δ
samples show an ordered arrangement of Ni and Mn atoms in the perovskite lattice. LaNi0.5Mn0.5O
3 + δ
is then, a double perovskite A2BB'O6 whereas Ni and Mn atoms are randomly distributed for the rest of the samples. X-ray magnetic circular dichroism experiments
confirm the presence of collinear ferromagnetism in LaNi0.5Mn0.5O
3 + δ
. The role of competitive magnetic interactions, structural disorder, magnetic anisotropy and magnetic disaccommodation is
also discussed
Received 19 July 2002 / Received in final form 23 October 2002 Published online 31 December 2002 相似文献
14.
G. Li S.-J. Feng F. Liu Y. Yang R.-K. Zheng T. Qian X.-Y. Guo X.-G. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):5-11
The magnetic transport properties have been measured for La0.67-xYxCa0.33MnO3 ( 0 ⩽
x
⩽ 0.14) system. It was found that the transition temperature T
p
almost linearly moves to higher temperature as H increases. Electron spin resonance confirms that above T
p
, there exist ferromagnetic clusters. From the magnetic polaron point of view, the shift of T
p
vs. H was understood, and it was estimated that the size of the magnetic polaron is of 9.7 ∼ 15.4 ? which is consistent with the magnetic correlation length revealed by the small-angle neutron-scattering technique. The
transport properties at temperatures higher than T
p
conform to the variable-range hopping mechanism.
Received 27 August 2002 / Received in final form 2 December 2002 Published online 14 March 2003 相似文献
15.
R.P. Singh R.K. Bhowmik S.S. Ghugre S.B. Patel 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):35-40
High spins states in 99Rh were populated via the 66Zn(37Cl, 2p2n)99Rh reaction at an incident beam energy of 130 MeV. Seventeen new transitions have been observed in the present study and the
level scheme has now been extended up to a spin of J∼ 25ħ and an excitation energy of about E
x∼ 10 MeV. The observation of a positive parity E2 cascade based on the 9/2+ isomeric level is suggestive of collective behaviour in this nucleus up to high spins. Spherical shell model (within restricted
model space) and Cranked shell model calculations were performed to obtain an insight into the observed level structure. The
new collective band observed up to a spin of J∼ 25ħ is suggested to be based on (πg
9/2
3) ⊗ (νg
7/2
2) quasi-particle excitations.
Received: 12 July 1999 / Revised version: 14 September 1999 相似文献
16.
Ph. Tordjeman C. Robert G. Marin P. Gerard 《The European physical journal. E, Soft matter》2001,4(4):459-465
In order to study the effect of the α,β crystalline structure of polypropylene (PP) on its mechanical properties, it is necessary
to prepare samples with variable α/β-phase content but with constant crystallinity and constant spherulite size. With this
objective, heat treatment was first defined to be applied to an isotactic PP containing a β nucleating agent in order to achieve
these conditions. Then study of the effect of the β-phase content on the tensile properties and fracture behaviour has been
done at room temperature. The mechanical properties at fracture were assessed by three-point bending tests and were analysed
on the basis of the “Essential Work of Fracture” (EWF). The results show that the elongation at fracture under tensile stress
and the “near” Plane-Strain Essential Work of Fracture, w
Ie, increase substantially with the β-phase content. Besides, Young's modulus and the yield stress in tensile tests decrease
slowly with the β-phase content. Finally, these results are analysed taking account the differences in structure of the α
and β spherulites.
Received 18 September 2000 and Received in final form 19 December 2000 相似文献
17.
S. Heinz E. Berdermann F. Heine O. Joeres P. Kienle I. Koenig W. Koenig C. Kozhuharov U. Leinberger M. Rhein A. Schröter H. Tsertos The ORANGE Collaboration at GSI 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):55-61
We present new results from measurements and simulations of positron spectra, originating from 238U + 181Ta collisions at beam energies close to the Coulomb barrier. The measurements were performed using an improved experimental
setup at the double-Orange spectrometer of GSI. Particular emphasis is put on the signature of positrons from Internal-Pair-Conversion
(IPC) processes in the measured e+-energy spectra, following the de-excitation of electromagnetic transitions in the moving Ta-like nucleus. It is shown by
Monte Carlo simulations that, for the chosen current sweeping procedure used in the present experiments, positron emission
from discrete IPC transitions can lead to rather narrow line structures in the measured energy spectra. The measured positron
spectra do not show evidence for line structures within the statistical accuracy achieved, although expected from the intensities
of the observed γ-transitions ( E
γ∼ 1250-1600 keV) and theoretical conversion coefficients. This is due to the reduced detection efficiency for IPC positrons,
caused by the limited spatial and momentum acceptance of the spectrometer. A comparison with previous results, in which lines
have been observed, is presented and the implications are discussed.
Received: 27 April 2000 / Accepted: 14 September 2000 相似文献
18.
Alessandro Torcini Paolo Politi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):519-529
Surface growth models may give rise to instabilities with mound formation whose typical linear size L increases with time (coarsening process). In one dimensional systems coarsening is generally driven by an attractive interaction
between domain walls or kinks. This picture applies to growth models for which the largest surface slope remains constant
in time (corresponding to model B of dynamics): coarsening is known to be logarithmic in the absence of noise ( L(t) ∼ ln t) and to follow a power law ( L(t) ∼t
1/3) when noise is present. If the surface slope increases indefinitely, the deterministic equation looks like a modified Cahn-Hilliard
equation: here we study the late stages of coarsening through a linear stability analysis of the stationary periodic configurations
and through a direct numerical integration. Analytical and numerical results agree with regard to the conclusion that steepening
of mounds makes deterministic coarsening faster : if α is the exponent describing the steepening of the maximal slope M of mounds ( M
α∼L) we find that L(t) ∼t
n: n is equal to for 1≤α≤2 and it decreases from to for α≥2, according to n = α/(5α - 2). On the other side, the numerical solution of the corresponding stochastic equation clearly shows that in the
presence of shot noise steepening of mounds makes coarsening slower than in model B: L(t) ∼t
1/4, irrespectively of α. Finally, the presence of a symmetry breaking term is shown not to modify the coarsening law of model
α = 1, both in the absence and in the presence of noise.
Received 28 September 2001 and Received in final form 21 November 2001 相似文献
19.
E.T. Seppälä M.J. Alava 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):407-424
We study the effect of an external field on (1 + 1) and (2 + 1) dimensional elastic manifolds, at zero temperature and with
random bond disorder. Due to the glassy energy landscape the configuration of a manifold changes often in abrupt, “first order”-type
of large jumps when the field is applied. First the scaling behavior of the energy gap between the global energy minimum and
the next lowest minimum of the manifold is considered, by employing exact ground state calculations and an extreme statistics
argument. The scaling has a logarithmic prefactor originating from the number of the minima in the landscape, and reads ΔE
1∼L
θ[ln(L
z
L
- ζ)]-1/2, where ζ is the roughness exponent and θ is the energy fluctuation exponent of the manifold, L is the linear size of the manifold, and Lz is the system height. The gap scaling is extended to the case of a finite external field and yields for the susceptibility
of the manifolds ∼L
2D + 1 - θ[(1 - ζ)ln(L)]1/2. We also present a mean field argument for the finite size scaling of the first jump field, h
1∼L
d - θ. The implications to wetting in random systems, to finite-temperature behavior and the relation to Kardar-Parisi-Zhang non-equilibrium
surface growth are discussed.
Received December 2000 and Received in final form April 2001 相似文献
20.
A. Guarino S. Ciliberto A. Garcimartın M. Zei R. Scorretti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):141-151
The acoustic emission of fracture precursors, and the failure time of samples of heterogeneous materials (wood, fiberglass)
are studied as a function of the load features and geometry. It is shown that in these materials the failure time is predicted
with a good accuracy by a model of microcrack nucleation proposed by Pomeau. We find that the time interval δt between events (precursors) and the energy ɛ are power law distributed and that the exponents of these power laws depend
on the load history and on the material. In contrast, the cumulated acoustic energy E presents a critical divergency near the breaking time τ which is E∼
. The positive exponent γ is independent, within error bars, on all the experimental parameters.
Received 31 July 2001 and Received in final form 17 December 2001 相似文献