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1.
Z.Á. Németh J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):87-101
In this second paper, using N = 3 polarized electrons (spinless fermions) interacting via a U/r Coulomb repulsion on a two dimensional L×L square lattice with periodic boundary conditions and nearest neighbor hopping t, we show that a single unpaired fermion can co-exist with a correlated two particle Wigner molecule for intermediate values
of the Coulomb energy to kinetic energy ratio r
s = UL/(2t
). This supports in an ultimate mesoscopic limit a possibility proposed by Andreev and Lifshitz for the thermodynamic limit:
a quantum crystal may have delocalized defects without melting, the number of sites of the crystalline array being smaller
than the total number of particles. When L = 6, the ground state exhibits four regimes as rs increases: a Hartree-Fock regime, a first supersolid regime where a correlated pair co-exists with a third fully delocalized
particle, a second supersolid regime where the third particle is partly delocalized, and eventually a correlated lattice regime.
Received 22 October 2002 Published online 23 May 2003
RID="a"
ID="a"e-mail: jpichard@cea.fr 相似文献
2.
B. Canals D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):439-447
Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are
studied for the exactly solvable infinite-component spin-vector model, D↦∞. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances
smaller than the correlation length, r
ξ
c∝ exp(T
*/T), correlations in the checkerboard-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy
of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures,
spin CFs decay as <
>∝ 1/r
2 in the range a
0≪r≪ξ
c∝T
-1/2, where a0 is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are very similar with
MC simulations, exact and analytical results for the classical Heisenberg model (D = 3) on the pyrochlore lattice. This shows that the ground state of the infinite-component spin vector model on the checkerboard
lattice is a classical spin liquid.
Received 16 November 2001 and Received in final form 12 February 2002 相似文献
3.
G. Katomeris F. Selva J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):401-412
In 1969, Andreev and Lifshitz have conjectured the existence of a supersolid phase taking place at zero temperature between
the quantum liquid and the solid. In this and a succeeding paper, we re-visit this issue for a few polarized electrons (spinless
fermions) interacting via a U/r Coulomb repulsion on a two dimensional L×L square lattice with periodic boundary conditions and nearest neighbor hopping t. This paper is restricted to the magic number of particles N = 4 for which a square Wigner molecule is formed when U increases and to the size L = 6 suitable for exact numerical diagonalizations. When the Coulomb energy to kinetic energy ratio r
s = UL/(2t
) reaches a value r
s
F ≈ 10, there is a level crossing between ground states of different momenta. Above r
s
F, the mesoscopic crystallization proceeds through an intermediate regime ( r
s
F < r
s < r
s
W ≈ 28) where unpaired fermions with a reduced Fermi energy co-exist with a strongly paired, nearly solid assembly. We suggest
that this is the mesoscopic trace of the supersolid proposed by Andreev and Lifshitz. When a random substrate is included,
the level crossing at r
s
F is avoided and gives rise to a lower threshold r
s
F(W) < r
s
F where two usual approximations break down: the Wigner surmise for the distribution of the first energy excitation and the
Hartree-Fock approximation for the ground state.
Received 21 June 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: jpichard@cea.fr 相似文献
4.
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
5.
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
6.
A. Hader A. Memsouk Y. Boughaleb 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):315-319
We have studied the scaling properties of diffusion fronts by numerical calculations based on the mean field approach in the
context of a lattice gas model, performed in a triangular lattice. We find that the height-height correlation function scales
with time t and length l as C(l, t) ≈l
α
f (t/l
α/β) with α = 0.62±0.01 and β = 0.39±0.02. These exponent values are identical to those characterising the roughness of the diffusion
fronts evolving through a square lattice [1,2], thus confirming their universality.
Received 14 November 2001 / Received in final form 20 April 2002 Published online 31 July 2002 相似文献
7.
R. Mélin D. Feinberg 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):101-114
We derive a microscopic transport theory of multiterminal hybrid structures in which a superconductor is connected to several
spin-polarized electrodes. We discuss the non-perturbative physics of extended contacts, and show that such contacts can be
well represented by averaging out the phase of the electronic wave function. The intercontact Andreev reflection and elastic
cotunneling conductances are identical if the phase can be averaged out, namely in the presence of at least one extended contact.
The maximal conductance of a two-channel contact is proportional to (e
2/h)(a
0/D)2exp[-D/ξ(ω*)], where D is the distance between the contacts, a0 the lattice spacing, ξ(ω) is the superconducting coherence length, and ω* is the cross-over frequency between a perturbative regime ( ω < ω*) and a non perturbative regime ( ω* < ω < Δ).
Received 18 June 2001 and Received in final form 17 January 2002 相似文献
8.
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
9.
On the basis of the experimental data on diffractive processes in πp, pp and pˉp collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive
quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality
of cross sections such as σtot
πp/σtot
pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion
and proton (antiproton) in the impact parameter space of quarks, σπ(r
1⊥, r
2⊥; s) and σp(r
1⊥, r
2⊥, r
3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r
i⊥−r
k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented.
Received: 15 December 1998 相似文献
10.
Current-voltage (J-V) and differential-conductivity-voltage ( dJ/dV-V) characteristics are analytically calculated at zero temperature for a point contact consisting of: two Peierls conductors
P
( = 1, 2) separated by an insulator (I). Here P is a conductor with charge density wave (CDW). The J-V and dJ/dV-V characteristics depend on the CDW phases ( = 1, 2) in the mean field approximation. To calculate them analytically we assumed, = ≡Δ where ( = 1, 2) are the energy gaps of P
( = 1, 2). The current J has a discontinuous jump at eV = 2Δ for ϕ
1 = ϕ
2≠ 0. The differential conductivity dJ/dV has a singularity at eV = 2Δ for ϕ
1 = ϕ
2≠ 0. The relation J(V,ϕ
1,ϕ
2) = - J(- V,ϕ
1 + π,ϕ
2 + π) is obtained.
Received 4 July 2001 and Received in final form 13 September 2001 相似文献
11.
H. Chamati D.M. Dantchev 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):89-99
The finite size behavior of the susceptibility, Binder cumulant and some even moments of the magnetization of a fully finite
O(n) cubic system of size L are analyzed and the corresponding scaling functions are derived within a field-theoretic ɛ-expansion scheme under periodic
boundary conditions. We suppose a van der Waals type long-range interaction falling apart with the distance r as r
- (d + σ), where 2 < σ < 4, which does not change the short-range critical exponents of the system. Despite that the system belongs
to the short-range universality class it is shown that above the bulk critical temperature T
c the finite-size corrections decay in a power-in-L, and not in an exponential-in-L law, which is normally believed to be a characteristic feature for such systems.
Received 8 August 2001 相似文献
12.
G.I. Japaridze S. Sarkar 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):139-144
A one-dimensional model of interacting electrons with on-site U, nearest-neighbor V, and pair-hopping interaction W is studied at half-filling using the continuum limit field theory approach. The ground state phase diagram is obtained for
a wide range of coupling constants. In addition to the insulating spin-density wave (SDW) and charge-density wave (CDW) phases
for large U and V, respectively, we identify a bond-charge-density-wave (BCDW) phase W < 0, | U - 2V| < | 2W| and a bond-spin-density-wave (BSDW) for W > 0, | U - 2V| < W. The possibility of bond-located ordering results from the site-off-diagonal nature of the pair-hopping term and is a special
feature of the half-filled band case. The BCDW phase corresponding to an enhanced Peierls instability in the system. The BdSDW
is an unconventional insulating magnetic phase, characterized by a gapless spin excitation spectrum and a staggered magnetization
located on bonds between sites. The general ground state phase diagram including insulating, metallic, and superconducting
phases is discussed. A transition to the η-superconducting phase at | U - 2V| ≪ 2t?W is briefly discussed.
Received 20 February 2002 / Received in final form 11 April 2002 Published online 19 July 2002 相似文献
13.
14.
We study stable “bookshelf” smectic-A structures within a very thin plane-parallel cell of thickness L in which the mismatch between surface preferred (d
s) and intrinsic (d0) smectic layer thicknesses occurs. The Landau-Ginzburg approach based on a complex smectic order parameter is used. For a
weak enough smectic positional anchoring strength W smectic layers adopt the modified bookshelf profile. In a thick enough cell with increasing W a lattice of edge dislocations is continuously formed at the confining surfaces and then depinned from them. The structure
with dislocations is formed when the condition d
0/(
d
0/d
s - 1) ∼ 2 is fulfilled, where is the positional surface anchoring extrapolation length. If the cell is thin enough the dislocations formed at opposite
cell plates annihilate and consequently the smectic layers adopt a locked bookshelf structure. This transition is discontinuous
and takes place when d
0/(L
d
0/d
s - 1) ∼ 5 is realized. To observe these transitions in a cell of thickness L∼ 1μm the conditions W∼ 10-6
J/m
2 and
d
0/d
s - 1∼ 5 . 10-4 have to be fulfilled. All the three qualitatively different structures coexist at the triple point.
Received 21 February 2002 相似文献
15.
V.Yu. Grishina L.A. Kondratyuk E.L. Bratkovskaya M. Büscher W. Cassing 《The European Physical Journal A - Hadrons and Nuclei》2000,9(2):277-285
We investigate the reactions πN↦a
0
N and pp↦da
0
+ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different
contributions to the cross-section of the reaction πN↦a
0
N. These results are used to calculate the differential and total cross-sections of the reaction pp↦da
0
+ within the framework of the two-step model in which two nucleons produce an a0-meson via π-meson exchange and fuse to a deuteron. The necessity of new measurements on a0 production and branching fractions (of its decay to the K
and πη channels) is emphasized for clarifying the a0 structure. Detailed predictions for the reaction pp→da
0
+ are presented for the energy regime of the proton synchrotron COSY-Jülich.
Received: 4 August 2000 / Accepted: 17 September 2000 相似文献
16.
Khin Swe Myint S. Shinmura Y. Akaishi 《The European Physical Journal A - Hadrons and Nuclei》2003,16(1):21-26
The significance of ΛΛ-Ξ N coupling in double-Λ hypernuclei has been studied. The Pauli suppression effect due to this coupling
in 6
ΛΛ He has been found to be 0.43MeV for the coupling strength of the NSC97e potential. This indicates that the free-space ΛΛ
interaction is stronger by an about 5° phase shift than that deduced from the empirical data of 6
ΛΛ He without including the Pauli suppression effect. In 5
ΛΛ He and 5
ΛΛ H, an attractive term arising from the ΛΛ-Ξ N conversion is enhanced by the formation of an alpha-particle in the intermediate
Ξ states. According to this enhancement, we have found that the ΛΛ binding energy ( ΔB
ΛΛ) of 5
ΛΛ He is about 0.27MeV larger than that of 6
ΛΛ He for the NSC97e coupling strength. This finding deviates from the general picture that the heavier is the core nucleus,
the larger is ΔB
ΛΛ.-1
Received: 17 July 2002 / Accepted: 27 September 2002 / Published online: 17 January 2003
RID="a"
ID="a"e-mail: akaishi@post.ket.jp
Communicated by A. Molinari 相似文献
17.
M. Vatasescu F. Masnou-Seeuws 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):191-204
The paper contains a time-dependent investigation of the tunneling effect observed in the photoassociation spectrum of Cs2 and attributed to the 0g
-(6s, 6p
3/2) double well. When by photoassociation of two cold cesium atoms a vibrational level of the outer well is populated, tunneling
is an efficient mechanism for transferring the population to the inner well (R < 15a
0), where spontaneous emission may lead to formation of cold molecules in low vibrational levels of the a
3Σ+
u(6s, 6s) electronic state. This tunneling effect is analyzed by wavepackets propagation, first considering the double well potential
alone, and following a packet made by a superposition of states initially located at large distances. Characteristic times
for the vibration dynamics, corresponding to a beating phenomenon between the two wells, to partial “revival” at large distances,
and to maxima in the population localized in the inner well are reported and discussed. Second, we simulate the two-channels
a
3Σ+
u(6s, 6s)↦0g
-(6s, 6p
3/2) photoassociation at detunings around 2.9 cm-1: the inner well can be populated either by the excitation of a vibrational level of the external well (resonant excitation),
or by tuning the photoassociation laser at the energy of the inner well level which displays tunneling (“off-resonance excitation”).
In the first case the photoassociation is efficient, while the tunneling probability is small; in the second, the tunneling
probability is large, so that despite the poor efficiency of the photoassociation process, more population can be transferred
to the inner well. This second choice is shown to be very sensitive to the laser intensity, which could be used to control
the population of the inner well and hence the formation of ultracold molecules in low vibrational levels.
Received 19 April 2002 Published online 1st October 2002
RID="a"
ID="a"e-mail: francoise.masnou@lac.u-psud.fr 相似文献
18.
Y.C. Shin M.K. Cheoun K.S. Kim T.K. Choi 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):87-93
A role of the axial-vector mesons, such as K1 and a1, on the emitted-photon spectrum in hot hadronic matter is studied through the channels πρ→a
1→πγ and Kρ→K
1→Kγ. Both channels could be dominant over the region lower than E
γ∼ 0.5 GeV, while the role of the K1 meson is diminished in the higher E
γ region. This study is carried out with an SU
L(3) ⊗SU
R(3) effective chiral Lagrangian which includes vector and axial-vector mesons systematically and explains well their hadronic
and radiative decays simultaneously.
Received: 8 August 2001 / Accepted: 4 February 2002 相似文献
19.
M. Vojta R. Bulla 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):283-287
We consider a Kondo impurity coupled to a fermionic host with a power-law density of states near the Fermi level, ρ(ε) ∼ |ε|r, with exponent r < 0. Using both perturbative renormalization group (poor man's scaling) and numerical renormalization group methods, we analyze
the phase diagram of this model for ferromagnetic and antiferromagnetic Kondo coupling. Both sectors display non-trivial behavior
with several stable phases separated by continuous transitions. In particular, on the ferromagnetic side there is a stable
intermediate-coupling fixed point with universal properties corresponding to a fractional ground-state spin.
Received 18 February 2002 Published online 31 July 2002 相似文献
20.
T. Matulewicz L. Aphecetche Y. Charbonnier H. Delagrange K.K. Gudima G. Martınez M. Płoszajczak Y. Schutz V.D. Toneev M. Appenheimer R. Averbeck J. Dıaz A. Döppenschmidt M.J. van Goethem S. Hlavač M. Hoefman R. Holzmann F. Lefèvre A. Kugler H. Löhner A. Marın V. Metag R. Novotny R.W. Ostendorf R.H. Siemssen R.S. Simon R. Stratmann H. Ströher P. Tlusty P.H. Vogt V. Wagner J. Weiss H.W. Wilschut F. Wissmann A.R. Wolf M. Wolf 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):69-72
Proton-π0 coincidences have been measured at the beam energy of 180A MeV in the reaction Ar+Ca studied by TAPS at SIS/GSI. In the proton-π0 invariant mass spectrum we observe a significant excess of strength above the background obtained by event mixing. We attribute
this signal to the strength distribution N
Δ of the Δ baryonic resonance. No correlation is observed in the case of deuteron-π0 coincidences. Assuming isotropic emission of π0 and Δ+ from a midrapidity thermal source and isospin symmetry, we determined the global N
Δ/N
πratio of 0.79 ±0.30(stat) ±0.2(syst). This value indicates that most pions produced at subthreshold energy in heavy-ion reaction
are mediated by the Δ-resonance.
Received: 7 April 2000 / Accepted: 29 August 2000 相似文献