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1.
《Surface science》1996,365(3):L676-L680
We consider the non-equilibrium, time-dependent elastic-scattering structure factor S(q,t), for the disordering of an ordered overlayer, initially in equilibrium at temperature TI and characterized by the structure factor S(q,0)=x(q,TI, upon a sudden increase in temperature TITF at constant coverage, such that the adsorbates equilibrate at TF in a disordered phase. The initial decay of a peak in x(q,TI) proceeds exponentially in time, exp(−tτq), where τq is a wavevector-dependent lifetime, before it crosses over to a power-law, t−1 decay. When x(q,TI) is peaked at the boundaries of the Brillouin zone (BZ), the peak approximately maintains its shape in q-space as it decays exponentially. Except near the center of the BZ, after the peak has decayed sufficiently, the dependence of S(q,t) on q is as though the spins quasi-equilibrate to the equilibrium structure factor associated with TF, x(q,TF), in that the ratio S(q,t)x(q,TF) is independent of q, is dependent on time, approaching unity as t−1 for large t. For systems exhibiting an initial peak for q ≈ 0, the peak decays exponentially but does not preserve its shape, since τq strongly depends on q, diverging as q−2 for q→0. For these systems too, away from the center of the BZ, S(q,t)x(q,TF) rapidly evolves to a slowly decaying function of ttw, independent of q. In this case, however, the characteristic time scale, tw, is anomalously long, proportional to ξ2, where ξ is the correlation length associated with the initial state. This behavior of tw can be related to the random walk of domain boundaries.  相似文献   

2.
W.K. Theumann 《Physica A》1975,80(1):25-45
The order-parameter correlation function G?(q, ξ1) is calculated in the critical region of momentum space q in terms of a second-moment correlation length ξ1 by means of perturbation expansion to order 1/n, for an n-vector system with short-range interactions, in zero field above Tc, for 2 < d < 4. The scaling function of the q dependence is obtained in closed form with a precisely identified cutoff-dependent factor which is the amplitude of the correlation-length dependence of the susceptibility. Both the exponents and the coefficients of the expansion for fixed q as t = (T?Tc)/Tc → 0 are given explicitly and the former are shown to be in accordance with the operator product expansion. The coefficients of order 1/n in the terms associated with a tk(1?α) dependence of the energy density, for integer k ≥ 1, are expected to be explicitly cutoff-dependent and this is verified by the detailed calculations for k = 1. The behaviour for fixed t and q → 0 is shown to be markedly different from the Ornstein-Zernike approximation. Detailed comparison is provided with the scaling function of the t dependence of the correlations appearing in parallel work.  相似文献   

3.
Polarized Raman spectra were obtained in the quasi-one-dimensional conductor (TaSe4)2I above and below the charge-density-wave (CDW) transition temperature (Tc=263 K). The Raman intensities of many peaks become intenser and two of the phonon peaks shift to higher frequency with decreasing temperature. Moreover a new broad peak at about 90 cm?1 and a new peak around 166 cm?1 appear in the low-temperature phase. The polarization characteristic shows that the former is assigned to totally symmetric mode. The damping constant of the phonon at 90 cm?1 increases markedly with increasing temperature. The frequency shifts to higher frequency as the temperature increases and the coupling coefficient is approximately proportional to (Tc?T)12. This peak becomes Raman active owing to the CDW phase transition. The temperature dependence of the damping constant and the frequency shift may have a relation to the dynamical properties of the CDW phase transition.  相似文献   

4.
The Glauber dynamics of an Ising spin glass with infinite-range interactions and additional static field, h, is investigated near the freezing temperature, Tf. We obtain critical slowing down at and below the de Almeida-Thouless instability line, hc(T), to order (1?T/Tf)3 with algebraic decay of the spin correlations ~t, where ν=12 at Tf and ν≤12 for T<Tf.  相似文献   

5.
6.
The EPR line widths of the high and the low field resonances of Cr3+ in triglycine sulphate (TGS) show two distinct anomalous broadenings near Tc. One is associated with a change in the motional frequency of the hindered rotation of the NH3 groups and the other is related to the fluctuation of the polarization. Just below Tc there is a two fold splitting of the resonances which has a(Tc?T)12 temperature dependence indicating the local geometry about the Cr3+ ion is determined by mean field theory.  相似文献   

7.
J. Geicke 《Physics letters. A》1984,106(8):350-352
The Φ4 equation, linearized about a kink at rest, is solved for external driving fields F(t) = Σi=nfiti. The x-dependent part of the solution u?(x, t) is proportional to the translation mode. This implies that also for large times the kink's dynamics is adiabatic, if the external field is sufficiently weak and |u?|? z1|ν| ? 1.  相似文献   

8.
We studied the energy width and the width in reciprocal space Δq of the central mode of SrTiO3 above Tc. At Tc+4° we observed an energy width of about 6×10?7 eV. If the measured Δq is interpreted by a correlation length Δq?1 = ξ = ξ0??23 we obtain ξ0 = 75 A?.  相似文献   

9.
G. Lessner 《Physica A》1982,110(3):617-623
The osmotic coefficient of anomalous electrolytes up to concentrations c ≈ 1 mol/l is explained by the pair distributions n(r) = exp[-β(Vc(r) + V(hs)(r) + V1(r))]. Here Vc(r) is a screened Coulomb potential, V(hs)(r) a hard sphere potential and V1(r) = ?A/r6 a short range attractive potential. For the contact distances R++, R?? and R+? of the hard sphere potentials between ions with the same sign of their charges (++,??) and ions of opposite charges (+?) the relations R++ = R?? = R and R+? = q1R with 0 < q1 < 1 are assumed. In contrast to a previous paper the parameter q1 takes a fixed value q1 ≈ 0,8. The constant A is determined by the fraction q2 defined by A/R6 = q2(Z2e2/DR) where the positive integer Z is the charge number of the ions and D the dielectric constant of the solvent. The numerical calculation of the osmotic coefficient of 1-1-valent hydrous electrolytes in the range of temperature 273 K ? T ? 293 K shows that the anomalous electrolytes are described by fractions q2 in the range 0,25 ? q2 ? 0,5 if the contact distances R are in the range 3 A? ? R ? 7 A?.  相似文献   

10.
Flow birefringence is examined in classical fluids near the critical point under oscillating incompressible flows. This effect originates from anisotropy in the fluctuation part of the dielectric tensor in the presence of a flow and is found to be enhanced near the critical point. When the flow is stationary, the birefringence phase shift δ is proportional to ξ2D in the weak shear regime and to D13 in the strong shear regime where ξ is the correlation length and D is the shear rate. For the oscillatory case we examine only the weak shear regime. One characteristic feature is that δ becomes independent of T ? Tc when the frequency of the flow exceeds the average decay rate of critical fluctuations.  相似文献   

11.
The Curie temperatures of PdFe, PdCo, PtFe and PtCo alloys with Fe or Co concentrations between 1 and 10 at. % have been measured by thermal scanning of the 57Fe Mössbauer resonance under pressures up to 170 kbar. Systematically, the largest (positive) values of the logarithmic derivative, dlnTe/dlnV, are found in the most dilute alloys. The data are compared with models, which relate the variation of Tc under pressure to changes in the impurity spin-conduction electron coupling parameter, Ji, and to changes of the pure host metal susceptibility, χh. The discrepancies between the experimental data and these models are discussed.  相似文献   

12.
The equation of state obtained earlier /6/ for 3-dimensional Ising ferromagnets in the first order in1z (z is the number of the nearest neighbours) is generalized with regard to the classical D-component vector model. The results obtained are valid in a wide temperature range |τ|?[z2(D+2)]?1 (τ=(Tc-T)/Tc) and become exact in the limit D → ∞.  相似文献   

13.
The impurity resistivity of AlCr between 1.5 and 50°K was determined with a characteristic temperature for the T2 variation θ1=960±40°K. The behaviour of the resistivity minimum both in AlCr and AlMn alloys with impurity concentration provides evidence that a T3 phonon resistivity is found also in aluminium with anomalous impurity resistivity.  相似文献   

14.
For a non-conservative, classical system described by Lagrangian L(q?, qi, t), the functional Z = ?T0L dt + KT, where K is constant, is stationary with respect to variations in qi(t) and T, given suitable boundary conditions. In the conservative case, for systems with a single periodic coordinate, this variational procedure reduces to that given by Luttinger and Thomas.  相似文献   

15.
Modern high resolution inelastic neutron scattering methods make very long wavelength fluctuations accessible to dynamical investigation. The new results on Fe and EuO show that: (a) the q52 power law is well borne out at T = Tc; (b) strong zero-wavenumber relaxation due to spin non-conserving forces can make the predicted hydrodynamic spin diffusion at T >Tc unobservable; (c) this zero-wavenumber relaxation is the only appreciable deviation from the z = 52 exchange scaling behaviour; (d) there is no evidence for the predicted cross-over to dipolar dynamics a finite q's.  相似文献   

16.
The longitudinal conductivity of a quasi-one-dimensional metal is calculated for the case TDD being the limiting phonon frequency) and ωDl1/v?1 where l1 is the effective mean free path determined by impurity and phonon scattering: l1 = (l?1ph + l?1i)?1, lph = v/λT, li is the impurity mean free path. The conductivity is σ = (c1e2/πS)l3iv?2ωDλT for li?lph, σ = (c2e2/πS)D(λT)?2 for li?lph, λ being the dimensionless electron-phonon interaction constant, c1, c2 ~ 1, S = axay is the (xy) area per one chain.  相似文献   

17.
We have studied momentum spectra for D0 (D0) and D± mesons produced near 4 GeV in e+e? annihilation and find that production is dominated by two-body reactions involving D and D1 states where the D1 (charged and neutral) have masses near 2.01 GeV/c2. A detailed study of D momentum spectra near Ecm = 4.028 GeV allows determination of masses and branching ratios of D and D1 states. Lastly we find that events containing a D0 meson conserve strangeness, thus establishing upper limits on D0-D0 mixing and on the effects of charm changing neutral currents.  相似文献   

18.
577 events from pp→2π+? annihilations at 5.7 GeV/c are analyzed. Single-particle spectra are studied and an effective matrix element in the form Πi=14 exp(?BpTi2) is determined. The rates for production of ?° and f0 mesons are estimated and the influence of resonances on the angular distributions of pions and dipions is investigated. Transverse momenta correlations can be explained using peripheral phase space.  相似文献   

19.
The effect of pressure on the Curie temperature of the heavy rare-earth dialuminides has been measured up to 3.5 kbar. The derivatives dTc/dp are 0.00(4), 0.09, 0.21, 0.39, 0.60 and 0.71 K/kbar respectively for TmAl2 ErAl2, HoAl2, DyAl2, TbAl2 and GdAl2 thus indicating a clear positive correlation between dTc/dp and the de Gennes factor G. The results are discussed in terms of the RKKY model. However, the phenomenological parameter D/d, where D is the nearest-neighbour R-R distance and d the diameter of the 4f orbital, is used to reflect the non-δ-function character of the sf-coupling parameter Г. The experimental values of Г2D2 and Tp/G are found to decrease linearly with increasing D/d. This is in keeping with the RKKY proportionality of Tc?Tp to Γ2E?1FG. For GdAl2, TbAl2 and DyAl2 the quantity ? (dTcdp)kl(Dd)G coincides within the error limits with the slope of the Tp/G vs D/d plot.  相似文献   

20.
We present approximate analytic calculation of the functional derivative δTcδα2 (Ω)F(Ω), where Tc is the superconducting critical temperature and α2(Ω)F(Ω) is the electron-phonon spectral function, within the “square-well model” for the phonon mediated electron-electron interaction and weak coupling limit ωD(2πTc)? 1 (ωD is the Debye energy). It is found that δTcδα2(Ω)F(Ω) = (1 + λ)-1G(Ω) where λ is the familiar electron-phonon coupling parameter and G(Ω) is a universal function of the reduced frequency Ω = ΩTc. We compare this formula with accurate numerical results for several weak coupling superconductors. The overall agreement is good  相似文献   

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