共查询到20条相似文献,搜索用时 156 毫秒
1.
M. Dudzinski J. Sznajd J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):575-579
The zero temperature phase diagram of a one-dimensional ferromagnet with cubic single ion anisotropy in an external magnetic
field is studied. The mean-field approximation and the density-matrix renormalization group method are applied. Two phases
at finite magnetic fields are identified: a canted phase with spontaneously broken symmetry and a phase with magnetization
along the magnetic field. Both methods predict that the canted phase exists even for the single-ion anisotropy strong enough
to destroy the magnetic order at zero magnetic field. In contrast to the mean-field theory, the density-matrix renormalization
group predicts a reentrant behavior for the model. The character of the phase transition at finite magnetic field has also
been considered and the critical index has been found.
Received 9 May 2000 and Received in final form 5 July 2000 相似文献
2.
The Bethe lattice spin glass revisited 总被引:2,自引:0,他引:2
M. Mézard G. Parisi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):217-233
So far the problem of a spin glass on a Bethe lattice has been solved only at the replica symmetric level, which is wrong
in the spin glass phase. Because of some technical difficulties, attempts at deriving a replica symmetry breaking solution
have been confined to some perturbative regimes, high connectivity lattices or temperature close to the critical temperature.
Using the cavity method, we propose a general non perturbative solution of the Bethe lattice spin glass problem at a level
of approximation which is equivalent to a one step replica symmetry breaking solution. The results compare well with numerical
simulations. The method can be used for many finite connectivity problems appearing in combinatorial optimization.
Received 27 September 2000 相似文献
3.
A.S. Joshipura S.D. Rindani 《The European Physical Journal C - Particles and Fields》2000,14(1):85-89
We discuss an extended model which naturally leads to mass scales and mixing angles relevant for understanding both the solar and atmospheric neutrino
anomalies in terms of the vacuum oscillations of the three known neutrinos. The model uses a softly broken –– symmetry and contains a heavy scale GeV. The –– symmetric neutrino masses solve the atmospheric neutrino anomaly while breaking of –– generates the highly suppressed radiative mass scale needed for the vacuum solution of the solar neutrino problem. All the neutrino masses in the model are inversely related
to , thus providing seesaw-type of masses without invoking any heavy right-handed neutrinos. The possible embedding of the model
into an SU(5) grand unified theory is discussed.
Received: 5 August 1999 / Revised version: 18 November 1999 / Published online: 6 April 2000 相似文献
4.
K. Maschke T. Meier P. Thomas S.W. Koch 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):599-606
The coherent dynamics of magnetoexcitons in semiconductor nanorings following pulsed optical excitation is studied. The calculated
temporal evolution of the excitonic dipole moment may be understood as a superposition of the relative motion of electrons
and holes and a global circular motion associated with the magnetic-field splitting of these states. This dynamics of the
electron-hole pairs can be generated either by local optical excitation of an ordered ring or, alternatively, by homogeneous
excitation of rings with broken rotational symmetry due to disorder or band tilting.
Received 27 September 2000 相似文献
5.
I. Milosević T. Vuković M. Damnjanović B. Nikolić 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):707-712
The full geometrical symmetry groups (the line groups) of the monolayered, 2Hb and 3R polytypes of the inorganic MoS2 and WS2 micro- and nanotubes of arbitrary chirality are found. This is used to find the coordinates of the representative atoms sufficient
to determine completely the geometrical structure of the tubes. Then some physical properties which can be deduced from the
symmetry are discussed: electron band degeneracies, selection rules, general forms of the second rank tensors and potentials,
phonon spectra.
Received 13 April 2000 相似文献
6.
We apply the random-phase approximation (RPA) and its extension called renormalized RPA to the quantum anharmonic oscillator with an O(2) symmetry. We first obtain the equation for the RPA frequencies in the standard and in the renormalized RPAs using the equation-of-motion method. In the case where the ground state has a broken symmetry, we check the existence of a zero frequency in the standard and in the renormalized RPAs. Then we use a time-dependent approach where the standard-RPA frequencies are obtained as small oscillations arround the static solution in the time-dependent Hartree-Bogoliubov equation. We draw the parallel between the two approaches.Received: 8 July 2003, Published online: 5 January 2004PACS:
21.60.Jz Hartree-Fock and random-phase approximations - 24.10.Cn Many-body theory 相似文献
7.
D. Langevin 《The European physical journal. E, Soft matter》2001,5(1):81-85
Studies of thin liquid films, made from semidilute polyelectrolyte solutions, are presented. The disjoining pressure variation
with film thickness exhibits oscillations, corresponding to film stratification. The oscillations become sharper as the polymer
concentration c increases, and disappear when salt is added. The period of the oscillations scales as c
-1/2. The observed stratification is related to the polymer network and the size of the steps to the mesh size ξ.
Received 25 April 2000 and Received in final form 3 October 2000 相似文献
8.
R. Koç H. Tütüncüler M. Koca 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(3):467-472
It is now well-known that electron (hole)-vibron coupling and hence Jahn-Teller (JT) effect is important understanding the
properties of C60 and related molecules. In this paper, we study H(2) coupling case to find the potential energy surfaces for the positively charged C60 molecule due to distortion. The H(2) Jahn-Teller system is of particular importance as this will be the JT effect displayed by C60 molecules removed with an electron. C60
+ is obtained by removing one electron from fivefold degenerate Hu highest occupied molecular orbital (HOMO) and a hole in HOMO interacts with the vibrational modes of C60 and symmetry is broken. We apply the method of symmetry breaking mechanism to obtain expressions for the potential energy
surface.
Received 27 December 1999 and Received in final form 15 May 2000 相似文献
9.
R. Ramaswamy 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):339-343
Integrable dynamical systems, namely those having as many independent conserved quantities as freedoms, have all Lyapunov
exponents equal to zero. Locally, the instantaneous or finite time Lyapunov exponents are nonzero, but owing to a symmetry,
their global averages vanish. When the system becomes nonintegrable, this symmetry is broken. A parallel to this phenomenon
occurs in mappings which derive from quasiperiodic Schr?dinger problems in 1-dimension. For values of the energy such that
the eigenstate is extended, the Lyapunov exponent is zero, while if the eigenstate is localized, the Lyapunov exponent becomes
negative. This occurs by a breaking of the quasiperiodic symmetry of local Lyapunov exponents, and corresponds to a breaking
of a symmetry of the wavefunction in extended and critical states.
Received 25 October 2001 / Received in final form 8 December 2001 Published online 2 October 2002
RID="a"
ID="a"e-mail: r.ramaswamy@mail.jnu.ac.in 相似文献
10.
Z.Y. Zeng Y. Xiang L.D. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):699-705
We proposed a new kind of coupled coaxial cylindrical quantum wires structure - quantum cable, and calculated its single-electron
energy subband spectrum for the varying structure parameters, in order to investigate its subband motion in the structure
parameter space. It is shown that quantum cable has unique subband spectrum, which differs either from the (solid and hollow)
cylindrical quantum wire or from the usual coupled double quantum wires (CDQWs) structure. Aside from the two-fold degeneracy
induced by the cylindrical symmetry, crossings (accidental degeneracies) and anticrossings (repulsions) of quantum cable subbands
with different azimuthal and radial quantum numbers are observed as one of the cable structure parameters varies. This introduces
the dependence of the subband ladder on the structure parameters of the quantum cable structure. However, the subband with
the lowest azimuthal and radial quantum numbers remains the lowest subband and never crosses with the other subbands irrespective
of the value of structure parameters. As the coupling barrier is broadening (coupling becoming weak), some subbands bundling
toward another subband is seen before the extreme isolating limit achieved. Moreover, the separation between neighboring subbands
exhibits non-monotonous evolution as one changes the thickness of one of the cylindrical quantum wires, with a minimum existing
in the separation between some two adjacent subbands. Interesting optical and transport phenomena arising from these unique
subband properties of the quantum cable structure are also predicted.
Received 22 March 2000 and Received in final form 6 June 2000 相似文献
11.
K. Esfarjani A.A. Farajian F. Ebrahimi Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):353-355
Transport properties of doped nanotube-based double junctions forming a nanotransistor are investigated within the tight binding
formalism. The effects of doping, gate length and gate-source hopping have been considered. It is found that in addition to
the importance of rotational symmetry in determining transport properties, large gains can be achieved for semiconducting
doped tubes.
Received 30 November 2000 相似文献
12.
Ll. Serra A. Puente 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):77-81
The magnetic extension of the Thomas-Fermi-Weizs?cker kinetic energy is used within density-functional-theory to numerically
obtain the ground state densities and energies of two-dimensional quantum dots. The results are thoroughly compared with the
microscopic Kohn-Sham ones in order to assess the validity of the semiclassical method. Circular as well as deformed systems
are considered.
Received 26 October 2000 and Received in final form 14 December 2000 相似文献
13.
I. Josopait L. Dobrek L. Santos A. Sanpera M. Lewenstein 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):385-391
The atom optics of Bose-Einstein condensates containing a vortex of circulation one is discussed. We first analyze in detail
the reflection of such a condensate falling on an atomic mirror. In a second part, we consider a rotating condensate in the
case of attractive interactions. We show that for sufficiently large nonlinearity the rotational symmetry of the rotating
condensate is broken.
Received 16 September 2002 / Received in final form 17 November 2002 Published online 11 February 2003 相似文献
14.
M.A. Itskovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):283-296
Theory of magnetoquantum oscillations with spin-split structure in strongly anisotropic (two-dimensional (2D)) metal is developed
in the formalism of level approach. Parametric method for exact calculation of oscillations wave forms and amplitudes, developed
earlier for spin degenerate levels is generalized on a 2D electron system with spin-split levels. General results are proved:
1) proportionality relation between magnetization and chemical potential oscillations accounting for spin-split energy levels
and magnetic field unperturbed levels (states of reservoir), 2) basic equation for chemical potential oscillations invariant
to various models of 2D and 1D energy bands (intersecting or overlapping) and localized states. Equilibrium transfer of carriers
between overlapping 2D and 1D bands, characterizing the band structure of organic quasi 2D metals, is considered. Transfer
parameter, calculated in this model to be of the order of unity, confirms the fact that the wave form of oscillations in organic metals should be quasisymmetric up to ultralow temperature. Presented theory accounts for spin-split magnetization oscillations at magnetic field directions tilted relative to the anisotropic
axis of a metal. Theoretical results are compared with available experimental data on organic quasi-2D metal α-(BEDT-TTF)2KHg(SNC)4 explaining the appearance of clear split structure under the kink magnetic field and absence above by the corresponding change
in the electron g-factor rather than cyclotron mass.
Received 20 December 2000 and Received in final form 13 July 2001 相似文献
15.
An exact solution of electromagnetic wave scattering by a time reversal symmetry broken topological insulator sphere is researched. According to the constitute relations of topological insulator, we modified magnetic vector potential and electric vector potential of standard Mie theory and derived scattered electromagnetic fields and scattered coefficients. Numerical results show that, when the time reversal symmetry is broken, the extinction efficiencies and the scattering efficiencies are influenced by topological magneto-electric polarizability. 相似文献
16.
H. V. Klapdor-Kleingrothaus H. Päs U. Sarkar 《The European Physical Journal A - Hadrons and Nuclei》2000,8(4):577-580
We discuss violations of CPT and quantum mechanics due to interactions of neutrinos with space-time quantum foam. Neutrinoless
double beta decay and oscillations of neutrinos from astrophysical sources (supernovae, active galactic nuclei) are analysed.
It is found that the propagation distance is the crucial quantity entering any bounds on EHNS parameters. Thus, while the
bounds from neutrinoless double beta decay are not significant, the data of the supernova 1987a imply a bound being several
orders of magnitude more stringent than the ones known from the literature. Even more stringent limits may be obtained from
the investigation of neutrino oscillations from active galactic nuclei sources, which have an impressive potential for the
search of quantum foam interactions in the neutrino sector.
Received: 5 June 2000 / Accepted: 12 July 2000 相似文献
17.
A. Dragulescu V.M. Yakovenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):723-729
In a closed economic system, money is conserved. Thus, by analogy with energy, the equilibrium probability distribution of
money must follow the exponential Boltzmann-Gibbs law characterized by an effective temperature equal to the average amount
of money per economic agent. We demonstrate how the Boltzmann-Gibbs distribution emerges in computer simulations of economic
models. Then we consider a thermal machine, in which the difference of temperatures allows one to extract a monetary profit.
We also discuss the role of debt, and models with broken time-reversal symmetry for which the Boltzmann-Gibbs law does not
hold. The instantaneous distribution of money among the agents of a system should not be confused with the distribution of
wealth. The latter also includes material wealth, which is not conserved, and thus may have a different (e.g. power-law) distribution.
Received 22 June 2000 相似文献
18.
Back-side-coated chirped mirrors with ultra-smooth broadband dispersion characteristics 总被引:1,自引:0,他引:1
N. Matuschek L. Gallmann D.H. Sutter G. Steinmeyer U. Keller 《Applied physics. B, Lasers and optics》2000,71(4):509-522
We demonstrate a new technique for the design of chirped mirrors with extremely smooth dispersion characteristics over an
extended ultra-broadband wavelength range. Our approach suppresses spectral dispersion oscillations, which can lead to unwanted
strong spectral modulations and limit the bandwidth of mode-locked laser pulses. Dispersion oscillations are significantly
reduced by coating the chirped mirror structure on the back side of a substrate, providing ideal impedance matching between
coating and ambient medium. An anti-reflection coating may be added on the front side of the substrate, geometrically separated
from the chirped mirror. The chirped mirror structure and the anti-reflection coating are non-interfering and can be independently
designed and optimized. The separation of both coating sections provides a much better solution for the impedance-matching
problems than previous approaches to chirped mirror design. We show by a theoretical analysis and numerical simulations that
minimum dispersion oscillations are achieved if the index of the substrate is identical to the index of one of the coating
materials and if double-chirping is used for the chirped mirror structure. Based on this analysis, we design a mirror that
supports a bandwidth of 220 THz with group delay dispersion oscillations of about 2 fs2 (rms), an order-of magnitude improvement compared to previous designs of similar bandwidth. In a first experimental demonstration
of back-side-coated (BASIC) mirrors, we achieve nearly transform-limited and virtually unchirped pulses of 5.8 fs duration
from a Kerr-lens mode-locked Ti:sapphire laser. BASIC mirrors are particularly suited for higher-order dispersion compensation
schemes. They support the extremely broad spectra of few-cycle pulses and promise to provide clean pulse shapes in this regime.
Received: 19 April 2000 / Published online: 6 September 2000 相似文献
19.
E. Brézin C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):353-358
One may impose to a system with spontaneous broken symmetry, boundary conditions which correspond to different pure states
at two ends of a sample. For a discrete Ising-like broken symmetry, boundary conditions with opposite spins in two parallel
limiting planes, generate an interface and a cost in free energy per unit area of the interface. For continuum symmetries
the order parameter interpolates smoothly between the end planes carrying two different directions of the order parameter.
The cost in free energy is then proportional to Ld-2 for a system of characteristic size L. The power of L is related to the lower critical dimension, and the coefficient of this additional free energy vanishes at the critical temperature.
In this note it is shown within a loop expansion that one does find the expected behavior of this twist free energy. This
is a preamble to the study of situations where the broken continuum symmetry is believed to be more complex, as in Parisi
ansatz for the Edwards-Anderson spin glass.
Received 11 June 2001 相似文献
20.
P. Paci C. Grimaldi L. Pietronero 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):235-243
The inclusion of nonadiabatic corrections to the electron-phonon interaction leads to a strong momentum dependence in the
generalized Eliashberg equations beyond Migdal's limit. For a s-wave symmetry of the order parameter, this induced momentum dependence leads to an enhancement of when small momentum transfer is dominant. Here we study how the d-wave symmetry affects the above behavior. We find that the nonadiabatic corrections depend only weakly on the symmetry of
the order parameter provided that only small momentum scatterings are allowed for the electron-phonon interaction. In this
situation, We show that also for a d-wave symmetry of the order parameter, the nonadiabatic corrections enhance . We also discuss the possible interplay and crossover between s- and d-wave depending on the material's parameters.
Received 12 May 2000 相似文献