共查询到20条相似文献,搜索用时 171 毫秒
1.
A.A. Zvyagin D.M. Apal'kov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):565-569
We present a Bethe Ansatz based investigation of a one-dimensional (1D) Heisenberg spin chain in a real 3D crystal lattice.
We have shown that due to an influence of the lattice distortion on a crystalline field of ligands of magnetic ions, a Heisenberg
antiferromagnetic spin chain is unstable under the appearance of a magnetic anisotropy of the “easy-plane” type. The effects of an external magnetic
field and nonzero temperature onto such a phase transition are studied.
Received: 19 January 1998 / Revised: 16 March 1998 / Accepted: 17 March 1998 相似文献
2.
3.
M. Sassetti B. Kramer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):357-367
The Raman spectra of quantum wires in the region of electronic intra-band excitations are investigated using one- and two-band
models based on the Luttinger approximation with spin. Structures related to charge and spin density modes are identified,
and analyzed with respect to their behavior with photon energy and temperature. It is found that the low-energy peaks in the
polarized spectra, close to resonance that are commonly assigned to “single particle excitations”, can be interpreted as the
signature of spin density excitations. A broad structure in the resonant depolarized spectrum is predicted above the frequency
of the spin density excitations. This is due to simultaneous but independent propagation of spin and charge density modes.
The results, when compared with experiment, show, that the electronic collective excitations of quantum wires at low energies
are characteristic for a non-Fermi liquid.
Received: 25 March 1998 / Accepted: 3 June 1998 相似文献
4.
L. Piraux S. Dubois A. Fert L. Belliard 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):413-420
A theory, based on earlier work by Valet and Fert, is first presented to describe the influence of temperature on the perpendicular
giant magnetoresistance (GMR) in multilayers. Then we present GMR measurements performed at T=77 K and at room temperature on Co/Cu multilayered nanowires with layer thicknesses ranging from a few nm to 1 μm. We use
our model to obtain a good quantitative fit to the experimental results in both the short spin diffusion length limit and
out of this limit. We discuss the temperature dependence of the bulk parameters, the scattering spin asymmetry coefficient
and spin diffusion length in the Co layers.
Received: 25 January 1998 / Accepted: 6 May 1998 相似文献
5.
Y.S. Lee M. Greven B.O. Wells R.J. Birgeneau G. Shirane 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):15-22
We report a neutron scattering study of the instantaneous spin correlations in the two-dimensional spin S
=5/2 square-lattice Heisenberg antiferromagnet Rb2MnF4. The measured correlation lengths are quantitatively described, with no adjustable parameters, by high-temperature series
expansion results and by a theory based on the quantum self-consistent harmonic approximation. Conversely, we find that the
data, which cover the range from about 1 to 50 lattice constants, are outside of the regime corresponding to renormalized
classical behavior of the quantum non-linear model. In addition, we observe a crossover from Heisenberg to Ising critical behavior near the Néel temperature; this crossover
is well described by a mean-field model with no adjustable parameters.
Received: 3 March 1998 / Received in final form: 4 May 1998 /
Accepted: 19 May 1998 相似文献
6.
C. Kohl S.M. El-Gammal F. Calvayrac E. Suraud P.-G. Reinhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):271-274
We investigate spin modes in the ground state and the polarized first isomer of the Na12 cluster describing the valence electrons in time-dependent local-spin-density approximation (TDLSDA) and the detailed ionic
background using local pseudopotentials. The spin modes show a collective redshift compared to the unperturbed particle-hole
excitations. They are strongly fragmented and the average energy of the modes along the principal axes are related to the
underlying geometry (triaxial or axially symmetric). For the polarized isomer, we find significant cross talk between the
spin modes and the dipole plasmon, which hints at a possible spectroscopic identification.
Received: 22 June 1998 / Accepted: 29 July 1998 相似文献
7.
Ding-wei Huang 《The European Physical Journal C - Particles and Fields》1998,5(3):567-574
Recent development of intermittency in the Ising model is reviewed. By means of various realization, the classical spin model
is adopted to study the particle number fluctuations and the intermittent behavior. The analytical expressions in one dimension
are obtained, both for the models with and without an external field. The onset of intermittency in the Ising model is more
likely a characteristic of decoupling into one-dimensional subsystems.
Received: 16 August 1996 / Revised version: 10 February 1998 / Published online: 24 March 1998 相似文献
8.
M.-T. Jaekel S. Reynaud 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(1):9-21
We define quantum observables associated with Einstein localization in space-time. These observables are built on Poincaré
and dilatation generators. Their commutators are given by spin observables defined from the same symmetry generators. Their
shifts under transformations to uniformly accelerated frames are evaluated through algebraic computations in conformal algebra.
Spin number is found to vary under such transformations with a variation involving further observables introduced as irreducible
quadrupole momenta. Quadrupole observables may be dealt with as non commutative polarizations which allow one to define step
operators increasing or decreasing the spin number by unity.
Received: 11 December 1997 / Revised: 1st July 1998 / Accepted: 1st September 1998 相似文献
9.
M. Dumm M. Dressel M. Nicklas P. Lunkenheimer A. Loidl M. Weiden F. Steglich B. Assmann H. Homborg P. Fulde 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):317-322
The magnetic susceptibility, using dc and electron spin resonance (ESR) methods, the specific heat, and the infrared properties
of the one-dimensional molecular semiconductors lithium phthalocyanine (LiPc) and the iodinated compound LiPcI have been investigated
for temperatures K. LiPc has a half-filled conduction band and is expected to be an organic metal. However, due to the strong Coulomb repulsion
the system is a one-dimensional Mott-Hubbard insulator with a Hubbard gap of 0.75 eV as inferred from optical measurements.
The localized electrons along the molecular stacks behave like a S = 1/2 antiferromagnetic spin chain. The spin susceptibility, as determined by ESR experiments, and the magnetic contribution
to the heat capacity show a Bonner-Fisher type of behavior with an exchange constant K. LiPcI is an intrinsic narrow-gap semiconductor with an optical gap of 0.43 eV. In ESR experiments it is silent, indicating
that all the unpaired electrons have been removed from the macrocycle via doping with iodine.
Received: 16 June 1998 / Accepted: 14 July 1998 相似文献
10.
K. Totsuka 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):705-717
Novel massive quantum states appearing in spin chains under a strong magnetic field are discussed. These states lead to plateaus in magnetization
curves. When the systems are axially symmetric and the field is applied parallel to the symmetry-axis, the phenomena are analogous
to metal-insulator transitions. Striking features of the plateau phenomena - exactness and rationality - are explained as
consequences the commensurability condition to the underlying lattice. The effects of the planar anisotropy are also discussed
in detail.
Received: 16 February 1998 / Revised: 20 April 1998 / Accepted: 30 April 1998 相似文献
11.
12.
Y.K. Gambhir J.P. Maharana C.S. Warke 《The European Physical Journal A - Hadrons and Nuclei》1998,3(3):255-262
The existence of broken pseudo-spin symmetry in the Pb nucleus has been studied in the relativistic mean field approach using
realistic Lagrangian parameters. Its relationship to spin orbit splitting and the vanishingly small surface delta character
of the mean spin orbit potential are investigated. In the 208Pb nucleus the broken pseudo-spin doublets are found to exist above the neutron (proton) Fermi surfaces.
Received: 16 April 1998 / Revised version: 26 June 1998 相似文献
13.
A. Joly J. Gascon P. Taras 《The European Physical Journal C - Particles and Fields》1999,6(3):413-419
The strange baryon production rates measured at LEP are compared to several models: isospin, LPHD, QCM, Jetset, Herwig and MOPS. In particular, the parameters of the new MOPS model are adjusted in an attempt to reproduce the spin and strangeness
dependence of the observed rates.
Received: 8 April 1998 / Revised version: 27 August 1998 / Published online: 19 November 1998 相似文献
14.
A. Tomiyama S. Suga A. Okiji 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):351-359
The elementary excitation spectrums for the Anderson model at finite temperatures are calculated by using the Bethe-ansatz
solution. The formulation is based on the method of Yang and Yang, which was developed for the one-dimensional boson systems
with the -function type interaction. We obtain the temperature dependence of the spin and the charge excitation spectrums. When the
impurity level lies deeply from the Fermi level and the Coulomb interaction is suitably large, the resonant peak structure
develops in the low energy region of the spin excitation spectrum and the hump structure grows around the impurity level of
the charge excitation spectrum with decreasing temperature.
Received: 21 January 1998 / Accepted: 17 March 1998 相似文献
15.
Qinghua Xu 《Frontiers of Physics》2015,10(6):101402
Both the PHENIX and STAR experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory are running polarized proton–proton collisions at s = 200 and 500 GeV. The main goal of the RHIC spin physics program is to gain deeper insight into the spin structure of the nucleon. We will give an overview of recent spin results from RHIC, particularly the study of gluon polarization via jet/hadron production and sea quark polarization via W boson production in longitudinally polarized proton–proton collisions. 相似文献
16.
In the past different models for the magnetic salt vanadyl pyrophosphate (VO)2P2O7 were discussed. Neither a spin ladder nor an alternating chain are capable to describe recently measured magnetic excitations.
In this paper we propose a 2D model that fits better to experimental observations.
Received: 29 May 1998 / Received in final form: 25 September 1998 / Accepted: 30 September 1998 相似文献
17.
W. Hofstetter W. Zwerger 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):751-756
We present a field-theoretic renormalization group calculation in two loop order for classical O(N)-models with an inverse square interaction in the vicinity of their lower critical dimensionality one. The magnetic susceptibility
at low temperatures is shown to diverge like with a=(N-2)/(N-1) and . From a comparison with the exactly solvable Haldane-Shastry model we find that the same temperature dependence applies also
to ferromagnetic quantum spin chains.
Received: 20 February 1998 / Revised: 27 April 1998 / Accepted: 30 April 1998 相似文献
18.
We introduce a new number-theoretic spin chain and explore its thermodynamics and connections with number theory. The energy
of each spin configuration is defined in a translation-invariant manner in terms of the Farey fractions, and is also expressed
using Pauli matrices. We prove that the free energy exists and a phase transition occurs for positive inverse temperature
β= 2. The free energy is the same as that of related, non-translation-invariant number-theoretic spin chain. Using a number-theoretic
argument, the low-temperature (β > 3) state is shown to be completely magnetized for long chains. The number of states of
energy E= log(n) summed over chain length is expressed in terms of a restricted divisor problem. We conjecture that its asymptotic form is
(n log n), consistent with the phase transition at β= 2, and suggesting a possible connection with the Riemann ζ-function. The spin
interaction coefficients include all even many-body terms and are translation invariant. Computer results indicate that all
the interaction coefficients, except the constant term, are ferromagnetic.
Received: 20 August 1998/ Accepted: 17 December 1998 相似文献
19.
T. Saikawa A. Ferraz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):17-22
Dynamical properties of the spin and charge response functions in the doped two-dimensional Hubbard model are calculated by
taking into account the drastic separation of the single-particle spectral function into the low-energy coherent and high-energy
incoherent parts due to the strong Coulomb interaction. We show that this evolution of the electronic states is the origin
of the broad and structureless feature in the charge response function. In the weak coupling regime the low-energy enhancement
of the spin excitation is produced which can be explained within the random phase approximation. However, for the larger interaction
close to the antiferromagnetic Stoner condition, the low-energy intensity of the spin excitation is suppressed.
Received: 25 September 1997 / Revised: 19 December 1997 / Accepted: 9 January 1998 相似文献
20.
Y.J. Kim M. Greven U.-J. Wiese R.J. Birgeneau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):291-297
Antiferromagnetic Heisenberg spin chains with various spin values (S=1/2,1,3/2,2,5/2) are studied numerically with the quantum Monte-Carlo method. Effective spin S chains are realized by ferromagnetically coupling n=2S antiferromagnetic spin chains with S=1/2. The temperature dependence of the uniform susceptibility, the staggered susceptibility, and the static structure factor
peak intensity are computed down to very low temperatures, . The correlation length at each temperature is deduced from numerical measurements of the instantaneous spin-spin correlation
function. At high temperatures, very good agreement with exact results for the classical spin chain is obtained independent
of the value of S. For the S=2 chain which has a gap , the correlation length and the uniform susceptibility in the temperature range are well predicted by the semi-classical theory of Damle and Sachdev.
Received: 23 December 1997 / Revised and Accepted: 11 March 1998 相似文献