共查询到20条相似文献,搜索用时 15 毫秒
1.
L.F. Chibotaru A. Ceulemans G. Teniers V. Bruyndoncx V.V. Moshchalkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):341-346
An approach to the Ginzburg-Landau problem of superconducting polygons is developed, based on the exact fulfillment of superconducting
boundary conditions along the boundary of the sample. To this end an analytical gauge transformation for the vector potential
A is found which gives A
n = 0 for the normal component along the boundary line of an arbitrary regular polygon. The use of the new gauge reduces the
Ginzburg-Landau problem of superconducting polygons in external magnetic fields to an eigenvalue problem in a basis set of
functions obeying Neumann boundary conditions. The advantages of this approach, especially for low magnetic fields, are illustrated
and novel vortex patterns are obtained which can be probed experimentally.
Received 28 February 2002 and Received in final form 12 April 2002 Published online 6 June 2002 相似文献
2.
G. Stenuit S. Michotte J. Govaerts L. Piraux 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):103-107
Theoretical and experimental magnetizations of lead nanowire arrays well below the superconducting transition temperature
Tc are described. The magnetic response of the array was investigated with a SQUID magnetometer. Hysteretic behaviour and phase
transitions have been observed in sweeping up and down the external magnetic field at different temperatures. The Meissner
and Abrikosov states were also experimentally observed in this apparently type-I superconductor. This fact brings to the fore
the non-trivial behaviour of the critical boundary κ
c ( = 1/ in bulk materials) between type-I and type-II phase transitions at mesoscopic scales. The time-independent Ginzburg-Landau
equations particularized to cylindrically symmetric configurations enable one to explain and reproduce the experimental magnetization
curves within 10% of error.
Received 16 January 2003 / Received in final form 27 March 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: stenuit@fynu.ucl.ac.be 相似文献
3.
D. Blaschke M.K. Volkov V.L. Yudichev 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):103-110
The phase diagram for quark matter is investigated within a simple Nambu-Jona-Lasinio model without vector correlations. It
is found that the phase structure in the temperature-density plane depends sensitively on the parametrization of the model.
We present two schemes of parametrization of the model where, within the first one, a first-order phase transition from a
phase with broken chiral symmetry to a color superconducting phase for temperatures below the triple point at T
t = 55 MeV occurs, whereas for the second one a second-order phase transition for temperatures below T
t = 7 MeV is found. In the latter case, there is also a coexistence phase of broken chiral symmetry with color superconductivity,
which is a new finding within this class of models. Possible consequences for the phenomenology of the QCD phase transition
at high baryon densities are discussed.
Received: 3 January 2003 / Accepted: 21 February 2003 / Published online: 24 April 2003 相似文献
4.
Electronic structure of three-dimensional quantum dots 总被引:1,自引:0,他引:1
T. Vorrath R. Blümel 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):227-235
We study the electronic structure of three-dimensional quantum dots using the Hartree-Fock approximation. The confining potential
of the electrons in the quantum dot is assumed to be spatially isotropic and harmonic. For up to 40 interacting electrons
the ground-state energies and ground-state wavefunctions are calculated at various interaction strengths. The quadrupole moments
and electron densities in the quantum dot are computed. Hund's rule is confirmed and a shell structure is identified via the addition energies and the quadrupole moments. While most of the shell structure can be understood on the basis of the
unperturbed non-interacting problem, the interplay of an avoided crossing and the Coulomb interaction results in an unexpected
closed shell for 19 electrons.
Received 5 November 2001 / Received in final form 12 November 2002 Published online 1st April 2003
RID="a"
ID="a"e-mail: vorrath@physnet.uni-hamburg.de 相似文献
5.
The two-channel Anderson lattice model which has SU
(2) ⊗
SU
(2) symmetry is of relevance to understanding of the magnetic, quadrupolar and superconducting phases in U1-xThxBe13 or Pr based skutterudite compounds such as PrFe4P12 or PrOs4Sb12. Possible unconventional superconducting phases of the model are explored. They are characterized by a composite order parameter
comprising of a local magnetic or quadrupolar moment and a triplet conduction electron Cooper-pair. This binding of local
degrees of freedom removes the entropy of the non Fermi-liquid normal state. We find superconducting transitions in the intermediate
valence regime which are suppressed in the stable moment regime. The gap function is non analytic and odd in frequency: a
pseudo-gap develops in the conduction electron density of states which vanishes as |ω| close to ω = 0. In the strong intermediate valent regime, the gap function acquires an additional -dependence.
Received 28 February 2002 / Received in final form 18 April 2002 Published online 9 July 2002 相似文献
6.
H. Capellmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):25-30
Superconductors put into rotation develope a spontaneous internal magnetic field (the “London field”). In this paper Ginzburg
Landau equations for order parameter, field, and current distributions for superconductors in rotation are derived. Two simple
examples are discussed: the massive cylinder and the “Little and Parks geometry”: a thin film of superconducting material
deposited on a cylinder of normal material. A dependence of T
c on rotational frequency is predicted. The magnitude of the effect is estimated and should be observable.
Received 28 May 2001 相似文献
7.
M. Giroud K. Hasselbach H. Courtois D. Mailly B. Pannetier 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):103-109
We present electrical transport experiments performed on submicron hybrid devices made of a ferromagnetic conductor (Co) and
a superconducting (Al) electrode. The sample was patterned in order to separate the contributions of the Co conductor and
of the Co-Al interface. We observed a strong influence of the Al electrode superconductivity on the resistance of the Co conductor.
This effect is large only when the interface is highly transparent. We characterized the dependence of the observed resistance
decrease on temperature, bias current and magnetic field. As the differential resistance of the ferromagnet exhibits a non-trivial
asymmetry, we claim that the magnetic domain structure plays an important role in the electron transport properties of superconducting
/ ferromagnetic conductors.
Received 9 July 2002 / Received in final form 22 October 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: herve.courtois@grenoble.cnrs.fr
RID="b"
ID="b"associated to Université Joseph Fourier 相似文献
8.
M. Romeo V. Da Costa F. Bardou 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):513-525
The lognormal distribution describing, e.g., exponentials of Gaussian random variables is one of the most common statistical distributions in physics. It can exhibit
features of broad distributions that imply qualitative departure from the usual statistical scaling associated to narrow distributions.
Approximate formulae are derived for the typical sums of lognormal random variables. The validity of these formulae is numerically
checked and the physical consequences, e.g., for the current flowing through small tunnel junctions, are pointed out.
Received 8 November 2002 / Received in final form 17 March 2003 Published online 7 May 2003 相似文献
9.
We introduce a solid-on-solid growth process which evolves by random deposition of dimers, surface diffusion, and evaporation
of monomers from the edges of plateaus. It is shown that the model exhibits a robust transition from a smooth to a rough phase.
The roughening transition is driven by an absorbing phase transition at the bottom layer of the interface, which displays
the same type of critical behavior as the pair contact process with diffusion 2A↦3A, 2A↦.
Received 14 October 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: Haye.Hinrichsen@physik.uni-wuppertal.de 相似文献
10.
C. Yannouleas U. Landman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):373-380
We show that the spin-and-space unrestricted Hartree-Fock method, in conjunction with the companion step of the restoration
of spin and space symmetries via Projection Techniques (when such symmetries are broken), is able to describe the full range of couplings in two-dimensional
double quantum dots, from the strong-coupling regime exhibiting delocalized molecular orbitals to the weak-coupling and dissociation
regimes associated with a Generalized Valence Bond combination of atomic-type orbitals localized on the individual dots. The
weak-coupling regime is always accompanied by an antiferromagnetic ordering of the spins of the individual dots. The cases
of dihydrogen (H2, 2e) and dilithium (Li2, 6e) quantum dot molecules are discussed in detail.
Received 19 December 2000 相似文献
11.
Zs. Podolyák P.G. Bizzeti A.M. Bizzeti-Sona S. Lunardi D. Bazzacco A. Dewald A. Algora G. de Angelis E. Farnea A. Gadea D.R. Kasemann T. Klug Th. Kröll S. Lenzi D.R. Napoli C.M. Petrache R. Peusquens C. Rossi Alvarez T. Martinez C.A. Ur 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):29-36
Lifetimes of excited states in 148Gd were measured using the recoil distance method with a plunger device coupled to the EUROBALL Ge detector array. The differential
decay curve method in coincidence mode allowed the unambiguous determination of lifetimes of more than 20 excited states.
The obtained transition strengths are in good agreement with the shell model calculations. The effect of the Z = 64 subshell closure on the B(E2 : 2+ → 0+) reduced strengths above the N = 82 magic number is discussed.-1
Received: 14 November 2002 / Accepted: 4 February 2003 / Published online: 29 April 2003 相似文献
12.
Y. Li Voskoboynikov C.P. Lee S.M. Sze O. Tretyak 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):475-481
In this article we study the impact of the spin-orbit interaction on the electron quantum confinement for narrow gap semiconductor
quantum dots. The model formulation includes: (1) the effective one-band Hamiltonian approximation; (2) the position- and
energy-dependent quasi-particle effective mass approximation; (3) the finite hard wall confinement potential; and (4) the
spin-dependent Ben Daniel-Duke boundary conditions. The Hartree-Fock approximation is also utilized for evaluating the characteristics
of a two-electron quantum dot system. In our calculation, we describe the spin-orbit interaction which comes from both the
spin-dependent boundary conditions and the Rashba term (for two-electron quantum dot system). It can significantly modify
the electron energy spectrum for InAs semiconductor quantum dots built in the GaAs matrix. The energy state spin-splitting
is strongly dependent on the dot size and reaches an experimentally measurable magnitude for relatively small dots. In addition,
we have found the Coulomb interaction and the spin-splitting are suppressed in quantum dots with small height.
Received 15 May 2001 / Received in final form 14 May 2002 Published online 13 August 2002 相似文献
13.
O. Bourgeois P. Gandit J. Lesueur A. Sulpice X. Grison J. Chaussy 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):75-80
We report transport measurements on Superconductor/Ferromagnet/Superconductor (S/F/S) junctions: Nb/Al/Gd/Al/Nb where gadolinium
(Gd) is a weakly polarized ferromagnet. A sizeable critical current I
c is observed in the I(V) characteristics. This current can be modulated by a weak magnetic field, as expected for a Josephson current. With these
experiments, we establish that superconducting coherent transport survives across a small ferromagnetic layer. The penetration
depth of Cooper pairs in Gd has been measured. An extensive study of the Josephson critical current in temperature for different
thicknesses of magnetic compounds is presented. A comparison of transport measurements with S/N/S junction is given through
measurements made on Nb/Al/Y/Al/Nb, where yttrium (Y) is used as non magnetic rare earth metal.
Received 20 September 2000 and Received in final form 22 February 2001 相似文献
14.
K. Van de Vel A.N. Andreyev R.D. Page H. Kettunen P.T. Greenlees P. Jones R. Julin S. Juutinen H. Kankaanpää A. Keenan P. Kuusiniemi M. Leino M. Muikku P. Nieminen P. Rahkila J. Uusitalo K. Eskola A. Hürstel M. Huyse Y. Le Coz M.B. Smith P. Van Duppen R. Wyss 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):167-171
Gamma rays from excited states of 190Po have been observed using the Jurosphere Ge-detector array coupled to the RITU gas-filled separator. They were associated
with a collective band which from spin 4 onwards resembles the prolate rotational bands known in the isotones 188Pb and 186Hg. This indicates that in 190Po the prolate configuration becomes yrast above I = 2. The experimental results are interpreted in a two-band mixing calculation and are in agreement with α-decay data and
potential energy surface calculations.
Received: 10 January 2003 / Accepted: 19 February 2003 / Published online: 7 May 2003 相似文献
15.
Yu.N. Ovchinnikov V.Z. Kresin 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):297-302
The relaxation of an electron excited to the high energy region, is accompanied by the creation of various excitations (plasmons,
quasi-particles, phonons). The stages of this many-body, non-stationary phenomenon (cascade) are described microscopically.
The electron distribution function n(ɛ, t) and characteristic times for the whole energy range, are calculated.
Received 7 February 2003 Published online 11 April 2003 相似文献
16.
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
17.
A. Vecchione M. Gombos S. Pace L. Marchese G. Cerrato C. Tedesco P.W. Stephens C. Noce 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):51-55
We report the preparation and the structural and morphological characterization of the perovskite compound NdSr2RuCu2Oy. The crystal structure of this material has been determined by a combined high-resolution electron microscopy, selected area
electron diffraction and high-resolution X-ray powder diffraction study. The morphology of the samples has been monitored
by a scanning electron microscope equipped with an energy dispersive spectrometer attachment by which the microanalysis of
the crystallites has been also performed. Finally, dc magnetic susceptibility measurements show that this compound behaves
like an enhanced paramagnetic metal with evidence of neither magnetic order and neither superconducting one.
Received 15 November 2001 相似文献
18.
M.P. Lissitski A. Naddeo C. Nappi A. Tagliacozzo V.N. Gubankov R. Monaco M. Russo 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):309-314
Measurements of differential resistance in a superconductor-degenerate semiconductor junction Nb
-
n
+ +
GaAs at T
= 1.6 K show close similarity to those for a conventional superconductor-insulator- normal metal junction, except for the position
of the minimum which is located at 3.6 meV. Using a simple model for the charge screening at the Schottky barrier, we give
an argument why this minimum is by far displaced with respect to the superconducting gap energy ( Δ
g
= 1.5 meV for bulk Nb). We argue that a rebuilding of the density of states takes place at the barrier, due to the imperfect metal
screening in the degenerate semiconductor. Energy states close to the degenerate semiconductor Fermi energy are depleted at
the barrier and are not available for tunneling, up to an energy Eg which adds to the superconducting gap Δ
g
.
Received 11 November 2002 / Received in final form 21 February 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: c.nappi@cib.na.cnr.it 相似文献
19.
Zhenhong Dai Jinzuo Sun Lide Zhang Maowang Lu Zuohong Li Shiyong Huang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):141-145
Artificial molecules, namely laterally coupled quantum dots with a three-dimensional spherical confinement potential well
of radius R and depth V
0, were studied by the unrestricted Hartree-Fock-Roothaan (UHFR) method. By varying the distance d between the centers of the two coupled quantum dots, the transition from the strong coupling situation to the weak one is
realized. Hund's rule, suitable for a single quantum dot is destroyed in certain conditions in the artificial molecule. For
example, in the few-electron system of the strongly coupled quantum-dot molecule, a transformation of spin configuration has
been found.
Received 8 March 2002 / Received in final form 29 May 2002 Published online 17 September 2002 相似文献
20.
Zhi Ping Wang Xi Xia Liang 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):265-271
Rayleigh-Schr?dinger perturbation theory and an improved Wigner-Brillouin perturbation theory has been used to study the cyclotron
resonance of the polarons in ternary mixed crystals in the zero-temperature limit. The interaction between an electron and
two branches of longitudinal optical phonon modes is taken into account in the framework of the random-element-isodisplacement
model. The numerical results for several ternary mixed crystals show that the polaronic cyclotron energy and mass split successively
twice related to the higher and lower branches of longitudinal optical phonon modes of ternary mixed crystals. A non-linear
dependence of the polaronic cyclotron energy and mass on the composition x is found.
Received 19 March 2002 / Received in final form 21 March 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: xxliang@imu.edu.cn 相似文献