共查询到20条相似文献,搜索用时 15 毫秒
1.
Y. Castin R. Dum 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):399-412
We investigate minimal energy solutions with vortices for an interacting Bose-Einstein condensate in a rotating trap. The
atoms are strongly confined along the axis of rotation z, leading to an effective 2D situation in the x-y plane. We first use a simple numerical algorithm converging to local minima of energy. Inspired by the numerical results
we present a variational ansatz in the regime where the interaction energy per particle is stronger than the quantum of vibration
in the harmonic trap in the x-y plane, the so-called Thomas-Fermi regime. This ansatz allows an easy calculation of the energy of the vortices as function
of the rotation frequency of the trap; it gives a physical understanding of the stabilisation of vortices by rotation of the
trap and of the spatial arrangement of vortex cores. We also present analytical results concerning the possibility of detecting
vortices by a time-of-flight measurement or by interference effects. In the final section we give numerical results for a
3D configuration.
Received 16 December 1998 and Received in final form 18 March 1999 相似文献
2.
Shi-Biao Zheng Guang-Can Guo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):105-107
We propose a method for preparing superpositions of coherent states of the motion of an ion in an anisotropic two-dimensional
trap, in which the ion is tightly bound in the y direction. In the scheme the ion is excited by two resonant laser beams with equal amplitude, propagating along the x and y directions, respectively. In the Dicke-Lamb limit, an initial coherent state of the ion motion can be converted into a superposition
of several coherent states on a circle through the laser-ion interactions and state-selective measurements on the ion.
Received: 30 May 1997 / Revised: 29 July 1997 / Accepted: 22 October 1997 相似文献
3.
P. Politi M.G. Pini 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):475-481
We study the effect of dipolar interactions on a magnetic striped monolayer with a microscopic unit cell of square symmetry,
and of size spins. Even if the aspect ratio r=N
x
/N
y
is very large, an in-plane shape anisotropy is always negligible, except if Ny is fairly small (N
y
<40). In-plane domains are not possible, except for values of the dipolar coupling larger than the domain wall energy.
Received: 11 July 1997 / Revised: 24 September 1997 / Accepted: 24 October 1997 相似文献
4.
G. Basappa N.V. Madhusudana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):179-187
We present experimental studies on the effect of strong electric fields on the nematogen p-cyanophenyl p-n-heptyl benzoate
which has the strongly polar cyano end group and a large positive dielectric anisotropy. We use a local temperature measurement
to take into account heating effects and an electrical impedance analysis to determine both the dielectric constant () and the resistance (R) of the sample. We also measure the higher harmonic responses of the medium. The new results obtained in this study are: (i)
a detailed temperature dependence of the terms which describe (a) the quenching of macroscopic thermal fluctuations of the
nematic director and (b) the enhancement of the orientational order parameter due to Kerr effect, (ii) clear evidence for
the critical divergence of susceptibility as reflected in the third harmonic signal, (iii) an unusual enhancement of the conductivity
which shows a large peak just below the critical point , (iv) a significant peak in the second harmonic signal at and (v) evidence for a field induced nematic-nematic transition well inside the nematic range. We argue that the results
(iii)-(v) indicate the presence of polar short range order in the medium and hence support a molecular model in which such an order has been proposed.
Received: 15 July 1997 / Received in final form: 24 September 1997 / Accepted: 29 October 1997 相似文献
5.
E. Plaut R. Ribotta 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):265-281
We study theoretically the formation of convection patterns in a laterally extended planar nematic layer heated from below,
in the linear and weakly nonlinear regimes. By reformulating the viscous coupling terms of the basic nematohydrodynamic equations,
a simple interpretation of the flow effects on the director dynamics can be proposed. A detailed linear analysis of the problem
is presented. A systematic method to investigate nonlinear mechanisms is developed, and exemplified by the study of the nonlinear saturation in rolls. The extension of the roll amplitude equation
with the envelope formalism is used to characterize the dynamics of the roll modulations near threshold. Coupled envelope
equations are shown to describe the structure of the point defects in zig-zags observed experimentally. Finally the bifurcation
to the bimodal varicose is studied. The secondary wavevector in the bimodal appears to be selected by a rotation of the director
in the horizontal plane. Quantitative predictions concerning the amplitude of this rotation are given.
Received: 1st December 1997 / Revised: 25 May 1998 / Accepted: 2 June 1998 相似文献
6.
Transmission resonances in magnetic-barrier structures 总被引:1,自引:0,他引:1
Y. Guo Z.-Q. Li B.-L. Gu Q. Sun J.-Z. Yu Y. Kawazoe 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):263-270
Quantum transport properties of electrons in simple magnetic-barrier (MB) structures and in finite MB superlattices are investigated
in detail. It is shown that there exists a transition of transmission resonances, i.e., from incomplete transmission resonances in simple MB structures consisting of unidentical blocks, to complete transmission
resonances in comparatively complex MB structures (, n is the number of barriers). In simple unidentical block arrangements in double- and triple-MB structures we can also obtain
complete transmission by properly adjusting parameters of the building blocks according to ky-value (ky is the wave vector in y direction). Strong suppression of the transmission and of the conductance is found in MB superlattices which are periodic
arrangements of two different blocks. The resonance splitting effect in finite MB superlattices is examined. It is confirmed
that the rule (i.e., for n-barrier tunneling the splitting would be (n-1)-fold) obtained in periodic electric superlattices can be extended to periodically arranged MB superlattices of identical
blocks through which electrons with tunnel, and it is no longer proper for electrons with k
y
<0 to tunnel.
Received: 18 August 1997 / Revised: 20 September 1997 / Accepted: 13 October 1997 相似文献
7.
Theoretical prediction of structural, electronic and optical properties of quaternary alloy Zn1-xBexSySe1-y 下载免费PDF全文
Within density functional theory based on the full potential-linearized augmented plane wave method, we carry out the first-principles calculation of the structural, electronic, and optical properties of the zinc blende quaternary alloy Zn1-xBexSySe1-y. The Perdew-Burke-Ernzerhof generalized gradient approximation based on the optimization of total energy and the Engel-Vosko generalized gradient approximation based on the optimization of the corresponding potential are used. Our investigation on the effect of the composition on lattice constants, bulk modulus, band gap, optical dielectric constant, and refractive index shows a non-linear dependence. The energy gap Eg(x, y) has been determined over the entire compositions x and y. In addition, the energy band gap of the technologically important quaternary alloy Zn1-xBexSySe1-y in conditions of being lattice matched to ZnS substrate has been investigated. It is noteworthy that the present work is the first theoretical study of the quaternary alloy of interest. 相似文献
8.
We have investigated the electronic structure, phonon modes and electron–phonon coupling to understand superconductivity in the ternary silicide NaAlSi with a layered diamond-like structure. Our electronic results, using the density functional theory within a generalized gradient approximation, indicate that the density of states at the Fermi level is mainly governed by Si p states. The largest contributions to the electron–phonon coupling parameter involve Si-related vibrations both in the x–y plane as well as along the z-axis in the x–z plane. Our results indicate that this material is an s-p electron superconductor with a medium level electron–phonon coupling parameter of 0.68. Using the Allen–Dynes modification of the McMillan formula we obtain the superconducting critical temperature of 6.98 K, in excellent agreement with experimentally determined value of 7 K. 相似文献
9.
Y. Li Y. -Q. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):493-500
We show that the efficiency of manipulating electron spins in semiconductor quantum wells can be enhanced by tuning strain
strengths. The combined effects of intrinsic and strain-induced spinorbit couplings vary for different quantum wells, which
provide an alternative route to understand the experimental phenomena brought in by the strain. The contribution to the electron-dipole-spin-resonance
intensity induced by the strain can be changed through adjusting the direction of the ac electric field in the x-y plane of the quantum well and tuning the strain strengths. 相似文献
10.
C. Tsallis D. Prato C. Anteneodo 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):605-611
We consider a statistical mixture based on that of two identical harmonic oscillators which is characterized by four parameters,
namely, the concentrations (x and y) of diagonal and nondiagonal bipartite states, and their associated thermal-like noises (T/α and T, respectively). The fully random mixture of two spins 1/2 as well as the Einstein-Podolsky-Rosen (EPR) state are recovered
as particular instances. By using the conditional nonextensive entropy as introduced by Abe and Rajagopal, we calculate a
bound for the separable-entangled frontier. Although this procedure is known to provide a necessary but in general not sufficient condition for separability, it does recover, in the particular case x = T = 0 ( ∀α), the 1/3 exact result known as Peres' criterion. The x = 0 frontier remarkably resembles to the critical line associated with standard diluted ferromagnetism where the entangled
region corresponds to the ordered one and the separable region to the paramagnetic one. The entangled region generically shrinks
for increasing T or increasing α.
Received 18 April 2002 / Received in final form 11 July 2002 Published online 31 October 2002
RID="a"
ID="a"e-mail: celia@cbpf.br 相似文献
11.
X.S. Chen V. Dohm D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):699-704
Using field theory and Monte Carlo (MC) simulation we investigate the finite-size effects of the magnetization M for the three-dimensional Ising model in a finite cubic geometry with periodic boundary conditions. The field theory with
infinite cutoff gives a scaling form of the equation of state where is the reduced temperature, h is the external field and L is the size of system. Below and at the theory predicts a nonmonotonic dependence of f(x,y) with respect to at fixed and a crossover from nonmonotonic to monotonic behaviour when y is further increased. These results are confirmed by MC simulation. The scaling function f(x,y) obtained from the field theory is in good quantitative agreement with the finite-size MC data. Good agreement is also found
for the bulk value at .
Received 20 July 1999 and Received in final form 11 November 1999 相似文献
12.
F. Maury I. Mirebeau M. Nicolas-Francillon F. Bourée 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):459-466
The magnetic structure of tetragonal insulating YBa2Cu3-xLixOy has been studied as a function of x and y. The Néel temperature and the mean ordered magnetic moment on the Cu2 sites were determined by neutron powder diffraction
measurements. The decrease of these two parameters as compared to YBa2Cu3O6 is much stronger for lithium than for zinc substitution. The difference is quantitatively explained by the presence of holes
created in the CuO2 planes. These holes arise from the substitution of plane Cu2+ by Li+. We suggest an explanation why such holes are not seen for the same substitution of plane Cu2+ by Li+ in orthorhombic superconducting YBa2Cu3-xLixO
7 - δ
.
Received 31 October 2001 and Received in final form 6 March 2002 Published online 25 June 2002 相似文献
13.
A series of (Ca1−x−y
Sr
x
)Si2O2N2:yEu2+ (x=0.0–0.97, y=0.03) phosphors were synthesized by high-temperature solid-state reaction. The XRD patterns confirm the formation of a solid
solution of (Ca1−x−y
Sr
x
)Si2O2N2:yEu2+. An intense tunable green light is observed with the increasing ratio of Sr/Ca. With an increase in x, the excitation and emission spectra show a redshift and blueshift, respectively, due to large centroid shift and small Stokes
shift. The temperature dependent luminescence is also investigated in the temperature range of 77–450 K. The Huang–Rhys factor
and the thermal-quenching temperature are determined. Intense green LEDs were successfully fabricated based on the (Ca1−x−y
Sr
x
)Si2O2N2:yEu2+ phosphor and near-ultraviolet (∼395 nm) GaN/blue (460 nm) InGaN chips. All the results indicate that the solid solution (Ca1−x−y
Sr
x
)Si2O2N2:yEu2+ is a promising phosphor applicable to near-UV and blue LEDs for solid-state lighting. 相似文献
14.
利用Chen-Mbius晶格反演获得的原子间相互作用势,对NaZn13型Fe基金属间化合物进行原子级模拟研究.计算结果表明,Si原子和Co原子均优先占据96i晶位,Si原子和Co原子替代Fe原子后晶体平均结合能降低.随着Co含量的增加,LaFe13-x-yCoySix和NdFe13-x-yCoySix的晶格参数逐渐降低.声子态密度中,稀土原子主要激发低频模,Si原子主要激发高频模.LaFe11.5-yCoySi1.5化合物的德拜温度随Co含量的增加而增高.
关键词:
晶格反演
原子间相互作用势
热力学性质
磁致冷材料 相似文献
15.
P. Galatola M. Zelazna I. Lelidis 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):51-56
We study the surface behavior of a semi-infinite smectogenic sample bounded by a solid wall, in the presence of an external
electric field. Our analysis is performed in the framework of a Landau-de Gennes theory. For the sake of simplicity, we consider
only the case in which, in the absence of field and surfaces, a direct isotropic to smectic-A transition occurs, while in
the presence of the electric field a nonspontaneous nematic phase appears. Two new surface phases are identified, namely a
parasmectic and a surface-induced smectic phase. The shifts in the transition temperatures and the critical behavior of the surface states are analyzed.
Received: 25 August 1997 / Accepted: 23 January 1998 相似文献
16.
17.
T. Charitat B. Fourcade 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):333-336
An o-ring takes spontaneously the shape of a chair when strong enough torsion is applied in its tangent plane. This state
is metastable, since work has to be done on the o-ring to return to the circular shape. We show that this metastable state
exists in a Hamiltonian where curvature and torsion are coupled via an intrinsic curvature term. If the o-ring is constrained to be planar (2d case), this metastable state displays a kink-anti-kink
pair. This state is metastable if the ratio is less than , where C and A are the torsion and the bending elastic constants [#!landau!#]. In three dimensions, our variational approach shows that
. This model can be generalized to the case where the bend is induced by a concentration field which follows the variations
of the curvature.
Received: 27 August 1997 / Revised: 23 October 1997 / Accepted: 12 November 1997 相似文献
18.
K.J. Wiese 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):273-276
The dynamical scaling properties of selfavoiding polymerized membranes with internal dimension D embedded into d dimensions are studied including hydrodynamical interactions. It is shown that the theory is renormalizable to all orders
in perturbation theory and that the dynamical scaling exponent z is given by z=d. The crossover to the region, where the membrane is crumpled swollen but the hydrodynamic interaction irrelevant is discussed.
The results apply as well to polymers (D=1) as to membranes (D=2).
Received: 5 September 1997 / Accepted: 17 November 1997 相似文献
19.
Large magnetoresistance (MR) has been observed in Ni1-
x
S (x=-0.02, -0.01, 0, 0.01, 0.02 and 0.03). The MR in a magnetic field of 4 T was found to be equal to 770% at 290 K for x=-0.02, 920% at 283 K for x=-0.01, 1530% at 268 K for x=0, 1040% at 230 K for x=0.01, 730% at 257 K for x=0.02 and 660% at 87 K for x=0.03. The large MR was found to be due to a magnetic field-induced magnetic and electrical transition from an antiferromagnetic
(AFM) anomalous-metal phase to a paramagnetic (PM) metal phase.
Received: 23 January 2001 / Accepted: 24 January 2001 / Published online: 27 June 2001 相似文献
20.
A gas source molecular beam epitaxial (GSMBE) growth model considering an intermediate InGaAsP state is presented. This model is very simple and needs only two fitting parameters, k
In and k
Ga, which are determined experimentally from In1-x
Ga
x
As
y
P1-y
on InP (0<x<0.47 and 0<y<1). At a growth temperature of 480°C, k
In and k
Ga are 28 and 3 respectively. The temperature dependencies of k
In and k
Ga are also studied: the fitted activation energies are-30 and 330 meV, respectively. Using these parameters, the model is used to predict the AsH3 and PH3 flow rates for growing In1-x
Ga
x
As
y
P1-y
on GaAs (0.51<x<1 and 0<y<1). The lattice mismatch of all the epilayers grown is within 6×10-4. This indicates that this simple GSMBE model covers the whole compositional range of lattice-matched and coherently strained InGaAsP. 相似文献