共查询到20条相似文献,搜索用时 31 毫秒
1.
A. Furrer H.-U. Güdel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):81-84
The inelastic neutron scattering technique was employed to study the magnetic excitation spectra in the diluted one-dimensional
Heisenberg antiferromagnet CsMn1-xMgxBr3 (x
=0, 0.05, 0.10, 0.25, 0.50). The spectral response is interpreted in terms of spin-wave excitations in finite chain segments
of Mn2+ ions, which are found to exist as long as the chain length exceeds twice the wavelength of the spin excitation. This limit
determines the crossover into the mesoscopic regime.
Received 31 December 1999 相似文献
2.
C. Djurberg K. Jonason P. Nordblad 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):15-21
Experiments on the temperature and time dependence of the response function and the field cooled magnetisation of a Cu(Mn)
spin glass at temperatures below the zero field spin glass temperature are used to explore the non-equilibrium nature of the
underlying spin configuration. The results imply that a certain spin configuration is imprinted on the system as the temperature
is decreased at a constant cooling rate. The cooling rate governs the magnitude of the FC magnetisation ((H,T)). Any intermittent halt at a constant temperature, , imprints an extended spin configuration, a process that is reflected e.g. in a downward relaxation of . On continued cooling at the same rate, the magnitude of (T) remains at a lower level than that of a continuous cooling curve. These results are put into the context of the corresponding
behaviour of the response function as observed in measurements of the relaxation of the zero field cooled magnetisation.
Received 27 October 1998 and Received in final form 30 November 1998 相似文献
3.
K.-V. Pham M. Gabay P. Lederer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):573-576
Standard bosonization techniques lead to phonon-like excitations in a Luttinger liquid (LL), reflecting the absence of Landau
quasiparticles in these systems. Yet in addition to the above excitations some LL are known to possess solitonic states carrying
fractional quantum numbers (e.g. the spin 1/2 Heisenberg chain). We have reconsidered the zero modes in the low-energy spectrum of the Gaussian boson LL Hamiltonian
both for fermionic and bosonic LL: in the spinless case we find that two elementary excitations carrying fractional quantum
numbers allow to generate all the charge and current excited states of the LL. We explicitly compute the wavefunctions of
these two objects and show that one of them can be identified with the 1D version of the Laughlin quasiparticle introduced
in the context of the Fractional Quantum Hall effect. For bosons, the other quasiparticle corresponds to a spinon excitation.
The eigenfunctions of Wen's chiral LL Hamiltonian are also derived: they are quite simply the one dimensional restrictions
of the 2D bulk Laughlin wavefunctions.
Received 26 January 1999 and Received in final form 21 April 1999 相似文献
4.
F. Ricoul M. Dubois T. Zemb D. Plusquellec 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):333-340
By use of a mean-field approach the spin-wave dispersion of the Cu degrees of freedom in the undoped high-T C material Nd2CuO4is investigated. The experimentally observed sharp decrease of the Cu spin-wave gap with increasing temperature in the range
is explained by a paramagnetic-like susceptibility of the Nd spins which couple to the Cu subsystem. The degeneracy of the
“in-plane” and “out-of-plane” polarized Cu spin-wave branches is shown to be lifted by the uniaxial anisotropy of the Cu-Cu
nearest-neighbor interaction.
Received: 13 August 1997 / Revised: 4 December 1997 / Accepted: 11 December 1997 相似文献
5.
M. Vojta K.W. Becker 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):427-435
We study frequency- and wave-vector dependent charge correlations in weakly doped antiferromagnets using Mori-Zwanzig projection
technique. The system is described by the two-dimensional t-J model. The ground state is expressed within a cumulant formalism which has been successfully applied to study magnetic properties
of the weakly doped system. Within this approach the ground state contains independent spin-bag quasiparticles (magnetic polarons).
We present results for the charge-density response function and for the optical conductivity at zero temperature for different
values of t
/
J. They agree well with numerical results calculated by exact diagonalization techniques. The density response function for
intermediate and large momenta shows a broad continuum on energy scales of order of several t whereas the optical conductivity for is dominated by low energy excitations (at 1.5-2J). We show that these weak-doping properties can be well understood by transitions between excited states of spin-bag quasiparticles.
Received: 10 July 1997 / Revised: 19 March 1998 / Accepted: 3 April 1998 相似文献
6.
M. Pletyukhov S. Konschuh 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(1):29-43
We analytically evaluate charge and spin density response functions of the
clean two-dimensional electron gas with Rashba spin-orbit coupling at finite
momenta and frequencies. On the basis of our exact expressions we discuss the
accuracy of the long-wavelength and the quasiclassical approximations. We also
derive the static limit of spin susceptibilities and demonstrate,
in particular, how the Kohn-like anomalies in their derivatives are related
to the spin-orbit modification of the Ruderman-Kittel-Kasuya-Yosida
interaction. Taking into account screening and exchange effects of the Coulomb
interaction, we describe the collective charge and spin density excitation
modes which appear to be coupled due to nonvanishing spin-charge response
function. 相似文献
7.
R. Egger A.O. Gogolin 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):281-300
We derive the effective low-energy theory for single-wall carbon nanotubes including the Coulomb interactions among electrons.
The generic model found here consists of two spin-fermion chains which are coupled by the interaction. We analyze the theory using bosonization, renormalization-group techniques,
and Majorana refermionization. Several experimentally relevant consequences of the breakdown of Fermi liquid theory observed
here are discussed in detail, e.g., magnetic instabilities, anomalous conductance laws, and impurity screening profiles.
Received: 12 December 1997 / Revised: 9 March 1998 / Accepted: 12 March 1998 相似文献
8.
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
9.
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
10.
H. Frahm C. Rödenbeck 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):409-414
We study the phase diagram of coupled spin-1/2 chains with bilinear and (chiral) three-spin exchange interactions in a magnetic
field. The model is soluble on a one-parametric line in the space of coupling constants connecting the limiting cases of a
single and two decoupled Heisenberg chains with nearest neighbour exchange only. We give a complete classification of the
low-energy properties of the integrable system and introduce a numerical method which allows to study the possible phases
of spin ladder systems away from the soluble line in a magnetic field.
Received 17 November 1998 and Received in final form 22
January 1999 相似文献
11.
A.A. Zvyagin A. Klümper J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):25-36
The exactly solvable model of supersymmetric t - J chains (STJC) of correlated electrons with next-nearest-neighbour (NNN) interactions is proposed and studied. The model with
interactions between nearest neighbours and NNN interactions in one chain can also be considered as a two-chain model with
zigzag-like coupling between the chains. The NNN interaction (coupling between chains) causes the onset of additional Dirac
seas for low-lying charge and/or spin excitations. These Dirac seas change the low-energy (conformal) behavior of the model.
The filling of those seas depends on the values of the NNN coupling (interactions between chains), external magnetic field
and applied voltage. We identify the new ground state phases which appear due to the NNN as incommensurate ones. The NNN coupling
in the incommensurate phases induces spontaneous magnetization and/or spontaneous filling of the Dirac sea for charge excitations
(“spontaneous charge ordering”). The onset of this order implies a first order quantum phase transition driven by the field
with hysteresis phenomena.
Received 13 September 2000 相似文献
12.
The Hubbard model on fcc-type lattices is studied in the dynamical mean-field theory of infinite spatial dimensions. At intermediate
interaction strength finite temperature Quantum Monte Carlo calculations yield a second order phase transition to a highly
polarized, metallic ferromagnetic state. The Curie temperatures are calculated as a function of electronic density and interaction
strength. A necessary condition for ferromagnetism is a density of state with large spectral weight near one of the band edges.
Received: 6 August 1997 / Accepted: 20 August 1997 相似文献
13.
K. Jonason P. Nordblad 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):23-28
Dynamic magnetic properties and ageing phenomena of the re-entrant ferromagnet (Fe0.20Ni0.80)75P16B6Al3 are investigated by time dependent zero field cooled magnetic relaxation, m(t), measurements. The influence of a temperature cycling (perturbation), ,(prior the field application) on the relaxation rate is investigated both in the low temperature re-entrant spin glass “phase”
and in the ferromagnetic phase. In the ferromagnetic phase the influence of a positive and a negative temperature cycle (of
equal magnitude) on the response is almost the same (symmetric response). The result at lower temperatures, in the RSG “phase”
is asymmetric, with a strongly affected response for positive, and hardly no influence on the response for negative temperature
cycles. The behaviour at low temperatures is similar to what is observed in ordinary spin glasses.
Received 20 August 1998 相似文献
14.
I.I. Satija 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):345-348
Disordered systems exhibiting exponential localization are mapped to anisotropic spin chains with localization length being
related to the anisotropy of the spin model. This relates localization phenomenon in fermions to the rotational symmetry breaking
in the critical spin chains. One of the intriguing consequence is that the statement of Onsager universality in spin chains
implies universality of the localized fermions where the fluctuations in localized wave functions are universal. We further
show that the fluctuations about localized nonrelativistic fermions describe relativistic fermions. This provides a new approach
to understand the absence of localization in disordered Dirac fermions. We investigate how disorder affects well known universality
of the spin chains by examining the multifractal exponents. Finally, we examine the effects of correlations on the localization
characteristics of relativistic fermions.
Received 28 September 2001 / Received in final form 30 November 2001 Published online 2 October 2002
RID="a"
ID="a"e-mail: isatija@nickel.nist.gov 相似文献
15.
16.
T.J. Smith H. Capellmann R.K. Kremer K-U. Neumann K.R.A. Ziebeck 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):341-347
A polarised neutron scattering investigation has been carried out on a powder sample of CuGeO3 within the temperature range of 1.5 K to 600 K. The magnetic scattering has been separated from all other contributions by
using polarised neutrons and polarisation analysis and placed onto an absolute scale. At low temperatures the long wavelength
components of the paramagnetic response are suppressed consistent with the formation of Cu dimers in which the magnetic moments
are correlated antiferromagnetically. This form of the scattering persists to temperatures well above the dimerisation temperature
T
sp
∼ 14 K. However as the temperature is raised the intensity of the long wavelength spin fluctuations increases and above ∼150 K they are the dominant feature in the wave vector dependence of the response. At all temperatures the observed scattering
extrapolates smoothly to the Q
= 0 value given by the uniform susceptibility. Consequently the thermal variation of the uniform susceptibility arises from the
evolution of the long wavelength magnetic fluctuations. At large wave vectors the energy dependence of the scattering revealed
that the response occurs below 16 meV in agreement with the reported maximum magnetic excitation energy at the zone boundary
in the ground state. However the total magnetic scattering is significantly less than that expected for a local moment system
suggesting that the spectrum of thermal and quantum fluctuations overlap.
Received 30 May 2000 and Received in final form 22 March 2001 相似文献
17.
F. Tedoldi A. Campana P. Carretta 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):219-223
μSR measurements in the antiferromagnetic (AF) phase of Ni1-xLixO for are reported. While in pure NiO the muon longitudinal depolarization rate is found almost temperature independent, in the Li-doped compounds broad maxima around 130 K are observed. These maxima are
associated with the progressive freezing of the spin fluctuations of S
=1/2 defects induced by the localization of the extra-holes. From the temperature dependence of and the stretched exponential form of the depolarization, insights on the distribution of correlation times for the fluctuating
field at the muon site are derived.
Received: 27 April 1998 / Received in final form and Accepted: 21 August 1998 相似文献
18.
A.V. Prokofiev F. Büllesfeld W. Assmus H. Schwenk D. Wichert U. Löw B. Lüthi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):313-316
Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)2P2O7. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating
spin chains. We determine J
=51 K and . Furthermore we find a spin gap of meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen
below 300 K.
Received: 22 December 1997 / Accepted: 17 March 1998 相似文献
19.
E. Rastelli A. Tassi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):341-347
Ferromagnetic spin chains of a hexagonal lattice coupled by a weak antiferromagnetic interaction J1 develop a helix arrangement if the intrachain antiferromagnetic NNN exchange J2 is sufficiently large. We show that the classical minimum energy spin configuration is an umbrella when an external magnetic field is applied. The scenario is dramatically changed by quantum fluctuations. Indeed we find
that the zero point motion forces the spins in a plane containing the magnetic field so that classical expectation is deceptive
for our model. Our result is obtained by controlled expansion in the low field-long wavelength modulation limit.
Received: 9 September 1997 / Revised: 15 October 1997 / Accepted: 17 November 1997 相似文献
20.
I. Kirschner C. Mészáros R. Laiho 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):191-196
It is shown that the line group formalism proposed is suitable to describe both commensurate and incommensurate modulations.
Symmetry groups of modulated crystal lattices can completely be characterized by symmetry transformations existing in real
space, without any application of the formalism based on reciprocal space. As typical examples of the method elaborated, the
fundamental invariance and symmetry properties of spin density functions and the soliton lattice are determined.
Received: 20 July 1997 / Accepted: 25 August 1997 相似文献