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1.
Levinson theorem for Dirac particles in one dimension 总被引:1,自引:0,他引:1
Qiong-gui Lin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(4):515-524
The scattering of Dirac particles by symmetric potentials in one dimension is studied. A Levinson theorem is established.
By this theorem, the number of bound states with even(odd)-parity, n+ (n-), is related to the phase shifts [] of scattering states with the same parity at zero momentum as follows: The theorem is verified by several simple examples.
Received 26 August 1998 and Received in final form 18 January 1999 相似文献
2.
P. Entel R. Meyer K. Kadau H.C. Herper E. Hoffmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):379-388
Results are presented of first-principles total-energy calculations and molecular-dynamics simulations of structural transformations
in magnetic transition metal alloys like Fe1-xNix. While first-principles calculations allow to identify those structures having the lower total energy, molecular-dynamics
simulations can be used to trace out the dependence of the transformation on temperature, composition, concentration of defects
etc. We have used the method of the semi-empiric embedded-atom potential in the molecular-dynamics simulations which yields remarkable
good results for the structural changes.
Received: 3 February 1998 / Revised: 4 May 1998 / Accepted: 24 June 1998 相似文献
3.
4.
Y. Chushak A. Baumketner 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(1):129-136
The dynamical properties of liquid alloys are investigated by means of memory function equations and molecular-dynamics simulation.
A simple model for the second-order memory function in a binary liquid, based on Mori's memory function formalism, is proposed
and applied in numerical calculations of the time correlation functions and dynamic structure factor of liquid K0.7Cs0.3 and K0.3Cs0.7 alloys. Obtained results are discussed in comparison with the results of computer simulations.
Received: 27 February 1998 / Revised: 24 July 1998 / Accepted: 27 July 1998 相似文献
5.
G. Mattei F. Toigo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):245-256
The effect of non-local norm-conserving pseudo-potentials on the static and dynamic properties of Nan and Lin cluster with n=6,8 is investigated in the frame of self-consistent LDA calculations with spherically averaged ionic density (SAPS model).
A comparison with previous calculations which use local pseudo-potentials as well with uniform averaged non-local pseudo-jellium
calculation has been carried out. A better quantitative agreement with experiments has been found in the calculation of the
photoresponse cross-section with respect to either simple jellium or pseudo-jellium model, even in very small clusters, where
deviations from sphericity are not negligible.
Received: 3 March 1998 / Received in final form and Accepted: 2 June 1998 相似文献
6.
T.M. Di Palma A. Latini M. Satta A. Giardini-Guidoni 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(2):225-229
A photoionization study of the Me(NH3) clusters formed in the reaction of photoablated third group metal vapor with gaseous ammonia is reported. The photoionization
spectra exhibit some features due to vibrational excitation of ionic clusters and to transitions to neutral Rydberg states
leading to autoionization. DFT quantum chemical calculations are performed on the Me(NH3). The cluster geometries are fully optimized imposing the C3v symmetry. The calculated values of the IPs are in agreement with those experimentally determined.
Received: 16 February 1998 / Revised and Accepted: 7 May 1998 相似文献
7.
G. Chaboussant M.-H. Julien Y. Fagot-Revurat M. Hanson L.P. Lévy C. Berthier M. Horvatic O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):167-181
In a magnetic field, spin-ladders undergo two zero-temperature phase transitions at the critical fields Hc1 and Hc2. An experimental review of static and dynamical properties of spin-ladders close to these critical points is presented. The
scaling functions, universal to all quantum critical points in one-dimension, are extracted from (a) the thermodynamic quantities
(magnetization) and (b) the dynamical functions (NMR relaxation). A simple mapping of strongly coupled spin ladders in a magnetic
field on the exactly solvable XXZ model enables to make detailed fits and gives an overall understanding of a broad class of quantum magnets in their gapless
phase (between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR relaxation demonstrates its Luttinger liquid nature as well as
the novel quantum critical regime at higher temperature. The general behavior close these quantum critical points can be tied
to known models of quantum magnetism.
Received: 13 March 1998 / Received in final form and Accepted: 21 July 1998 相似文献
8.
C. Humbert J.P. Decruppe 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):511-518
The optical and rheological properties of different viscoelastic solutions of surfactant are studied in order to gather experimental
data used to calculate the value of the stress optical coefficient C. Three surfactants of the same family (CTAB) have been chosen; they differ by the length of the hydrocarbon chain; it concerns
the dodecyltrimethylammonium bromide (C15H34BrN or DoTAB), the myristyltrimethylammonium bromide (C17H38BrN or MyTAB), and the hexadecyltrimethylammonium bromide (C19H42BrN or CTAB). Different parameters like the temperature of the solution and the salinity of the solvent have been made to
vary. Flow birefringence experiments and rheological measurements are performed on these solutions in order to study the dependence
of the extinction angle , of the birefringence intensity and of the shear stress with the shear rate . These data are used to check the stress optical law which turns out to be valid in a wide range of shear rates. The stress
optical coefficient C is then computed: it is found to vary with the salinity of the solvent and the temperature of the solution for a given surfactant.
Then, for all solutions of this work the variations of C are related to the variations of the polarizability anisotropy and the persistence length.
Received: 18 February 1998 / Revised: 23 June 1998 / Accepted: 22 July 1998 相似文献
9.
P.R. Dahoo I. Berrodier V. Raducu J.L. Teffo H. Chabbi A. Lakhlifi L. Abouaf-Marguin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(1):71-81
FTIR spectra of the antisymmetric stretch and symmetric bending vibrational modes of isotopic species of CO2 trapped in argon matrix are recorded at 5 K with a resolution of . A splitting of the mode is observed for the different species in the trapping site termed unstable. Considering this splitting and the width
of the line observed for this unstable site, one expects this site to be larger than the stable one. A theoretical model is elaborated
to interpret this splitting. Calculations performed at harmonic level of approximation for vibrational modes in a single substitutional
site (S1) and a double substitutional one (S2) in a fcc distorted argon lattice to minimize the free energy of the molecule-matrix
system, show the splitting to occur in the larger site. The latter result leads us to invert former attribution of the sites:
the stable site is a single substitutional one, whereas the unstable site is a double substitutional one.
Received: 27 January 1998 / Revised: 30 July 1998 / Accepted: 17 August 1998 相似文献
10.
V. Vescoli J. Favand F. Mila L. Degiorgi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):149-154
The validity of the optical sum rules has been addressed eversince and was always matter of debate. Particularly controversial
is the proof that the partial sum rules can be extended to both optical conductivity and energy loss function. We show in this paper that for both transverse
(optical conductivity) and longitudinal (energy loss function) absorption processes the corresponding sum rule can be theoretically
established and through appropriate conditions for the integration limits exactly verified. We also focus our attention on
the one-dimensional case within the microscopic Hubbard model. An application of these concepts to the quasi one-dimensional
systems, for which we have chosen the organic (TMTSF)2PF6 material, will also be presented.
Received: 19 December 1997 / Received in final form: 9 March 1998 / Accepted: 23 March 1998 相似文献
11.
S. Tresch R. Jacot-Guillarmod F. Mulhauser L.A. Schaller L. Schellenberg H. Schneuwly Y.-A. Thalmann A. Werthmüller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(2):93-97
The present status of research of muon transfer from the ground state of muonic protium to 4He is reviewed. The analysis of a recent measurement in a triple gas mixture of H2+4He+Ne at 15 bar and room temperature is presented and the result is compared to the existing experimental and theoretical
rates. The average muon transfer rate from protium to 4He determined from all lifetime measurements is .
Received: 22 January 1998 / Revised: 4 March 1998 / Accepted: 31 March 1998 相似文献
12.
C. Meneghini M. Maret V. Parasote M.C. Cadeville J.L. Hazemann R. Cortes S. Colonna 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):347-357
Polarized X-ray absorption fine structure (XAFS) measurements at the Co K and Pt L3 edges show that the perpendicular magnetic anisotropy found in epitaxial fcc CoPt3 (111) films stems from the existence of anisotropic local ordering. Such ordering, induced during the codeposition process
and dependent on the growth temperature, is characterized by preferential CoCo pairs in the film plane, balanced by preferential
CoPt pairs out of the plane, resulting from some Co 2D-segregation. Polarized XAFS at the Pt edge reveals similar anisotropic
local ordering in epitaxial hcp Co3Pt (0001) films exhibiting a larger magnetocrystalline anisotropy compared to that of bulk hcp Co. Besides, a polarization
dependence of the Co XANES profile is observed only for the Co3Pt films exhibiting hcp symmetry.
Received: 29 April 1998 / Revised: 27 July 1998 / Accepted: 31 August 1998 相似文献
13.
H. Yi J. Yu S.-I. Lee 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):509-512
To study the proposed phase separations in doped manganites, we performed Monte-Carlo calculations for the ferromagnetic Kondo
lattice model with strong Hund's coupling between conduction electrons and localized spins. For the practical calculations,
we adopted a one dimensional lattice and treated the spins of the localized t2g electrons semi-classically. A direct evidence of the phase separation is observed from a snapshot of the spatial dependence
of localized spins. No indication of the canted or spiral phases is found in the results of simulations. Further, the calculated
results of the spin structure factor in the phase separation region are well compared with recent experiments.
Received: 1st September 1998 / Revised: 30 October 1998 / Accepted: 27 November
1998 相似文献
14.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
15.
Y. Kuramoto 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):457-464
The poor man's scaling is extended to higher order by the use of the open-shell Rayleigh-Schr?dinger perturbation theory.
A generalized Kondo-type model with the SU(n)SU(m) symmetry is proposed and renormalized to the third order. It is shown that the model has both local Fermi-liquid and non-Fermi-liquid
fixed points, and that the latter becomes unstable in the special case of n=m=2. Possible relevance of the model to the newly found phase IV in CexLa1-xB6 is discussed.
Received: 24 February 1998 / Accepted: 17 April 1998 相似文献
16.
H.R. Brand P.E. Cladis H. Pleiner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):347-353
We discuss the macroscopic behavior of smectic CG liquid crystals. Smectic CG is the most general tilted smectic phase that is fluid in the layers. It is characterized by global C1 symmetry. Consequently, it is ferroelectric, pyroelectric and piezoelectric, opening up a number of possible applications
for such a phase. As smectic CG-phase has a macroscopic hand due to its structure, it is a natural candidate to explain the recent experimental observations
of left and right-handed helices in a system composed of achiral molecules. We also discuss critically to what extent smectic
CG could be important for liquid crystalline phases formed by banana-shaped molecules. Phase transitions involving a smectic
CG phase and defects of its in-plane director are briefly discussed.
Received: 25 March 1998 / Revised: 15 June 1998 / Accepted: 15 July 1998 相似文献
17.
M. Barat J.C. Brenot H. Dunet J.A. Fayeton Y.J. Picard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(3):271-276
An experimental study of the dissociation of the heteronuclear Na ion by collisions with He and H2 targets at a collision energy of 2.4 keV is presented. The use of a technique based on the measurement of the velocity vectors
of the fragments allows investigating in detail the two basic dissociation mechanisms: impulsive and electronic. In the present
asymmetric case, one is able to assess the relative role of close encounters with each of the Na+ and atomic cores of the molecule. Electronic transitions at a surface crossing are proposed to explain processes which happens
in close collisions between the core and the He target.
Received: 3 October 1997 / Revised: 1 December 1997 / Accepted: 16 January 1998 相似文献
18.
O. Toulemonde F. Studer A. Barnabé A. Maignan C. Martin B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):159-167
The XAS study at Cr, Co, Ni and Mn K-edges was performed for the doped CMR manganites Ln0.5Ca0.5Mn1-xBxO3 with Ln=La, Nd, Sm and B= Cr, Co, Ni (), on the samples that were studied previously for their ferromagnetic-metallic to antiferromagnetic-insulator transition.
We observed that the formal charges of the doping elements are Ni2+, Co2+ and Cr3+. It is also evidenced that the average formal charge of the manganese is increased after doping, in agreement with the charge
compensation keeping “O3” stoichiometry. These results suggest that the doping elements participate directly to the band structure.
Received: 9 January 1998 / Received in final form: 6 April 1998 / Accepted: 7 April 1998 相似文献
19.
R. Zeyher A. Greco 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):473-485
The feasibility of a perturbation expansion for Green's functions of the t-J model directly in terms of X-operators is demonstrated using the Baym-Kadanoff functional method. As an application we derive explicit expressions for
the kernel of the linearized equation for the superconducting order parameter in leading order of a 1/N expansion. The linearized equation is solved numerically on a square lattice taking instantaneous and retarded contributions
into account. Classifying the order parameter according to irreducible representations of the point group C4v of the square lattice and according to even or odd parity in frequency we find that a reasonably strong instability occurs
only for even frequency pairing with d-wavelike symmetry. The corresponding transition temperature Tc is where t is the nearest-neighbor hopping integral. The underlying effective interaction consists of an attractive, instantaneous term
and a retarded term due to charge and spin fluctuations. The latter is weakly attractive at low frequencies below ,strongly repulsive up to and attractive towards even higher energies. Tc increases with decreasing doping until a d-wavelike bond-order wave instability is encountered near optimal doping at for J=0.3. Tc is essentially linear in J and rather insensitive to an additional second-nearest neighbor hopping integral t'. A rather striking property of Tc is that it is hardly affected by the soft mode associated with the bond-order wave instability or by the Van Hove singularity
in the case with second-nearest neighbor hopping. This unique feature reflects the fact that the solution of the gap equation
involves momenta far away from the Fermi surface (due to the instantaneous term) and many frequencies (due to the retarded
term) so that singular properties in momentum or frequency are averaged out very effectively.
Received: 16 June 1998 / Accepted: 14 July 1998 相似文献
20.
D. Rönnow L.F. Lastras-Martínez M. Cardona 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):29-35
Within the past years the optical excitations of electrons have been measured for semiconductor samples of different isotope
compositions. The isotope shift observed have been compared with calculations of the effects of electron-phonon interaction
on the electronic band structure. While qualitative agreement has been obtained, some discrepancies remain especially concerning
the E1 and transitions. We have remeasured the effect of isotope mass on the E1 and transitions of germanium with several isotopic compositions. The results, obtained by means of spectroscopic ellipsometry,
confirm that the real part of the gap self-energies induced by electron-phonon interaction is larger than found from band
structure calculations, while the imaginary part agrees with those calculations, which are based on a pseudopotential band
structure and a bond charge model for the lattice dynamics. Our results agree with predictions based on the measured temperature
dependence of the gaps. We compare our data for E1 and with results for the lowest direct (E0) and indirect (Eg) gaps. The measured values of and increase noticeably with increasing isotope mass. Similar effects have been observed in the temperature dependence of in and . A microscopic explanation for this effect is not available.
Received: 6 March 1998 / Revised: 27 April 1998 /
Accepted: 15 May 1998 相似文献