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1.
The change of the sound velocity v(,T) and the damping of sound waves (,T) in spin glasses are calculated in the frame-work of an Ising model with a random distribution of exchange interactions. The calculation is based on linearized equations of motion for the spins and on an improved mean field approximation which includes the Onsager reaction field. Near to the freezing temperatureT f and at high temperatures v(,T) and (,T) turn out to be approximately proportional to the real and the imaginary parts of the dynamical susceptibility. For the special case of infinite range interactions atT=T f one has v(, Tf) ( )1/2 and (, Tf) (/)1/2 where is the relaxation time of independent spins. However, already slightly aboveT f the frequency dependence of both quantities becomes rather small for RKKY spin glasses. At high temperatures both, v(,T) and (,T) vary asT –1.SFB 125 Aachen-Jülich-Köln  相似文献   

2.
We present a modified London model suggested by Brandt [1–3] which introduces a finite vortex core size appropriate for isotropic superconductors in which the average internal field is less than approximately (1/4)H c2. TheSR lineshape resulting from this model possesses a distinctive shape due to the magnetic penetration depth and the vortex core diameter (approximately equal to twice the coherence length ). However, for a given lineshape, there is a large range of values of and which produce nearly the same lineshape. Lineshape smearing caused by disorder in the vortex lattice increases uncertainty in values for and . If well-determined values of either (T) or (T) are not available from another technique, both of them can be determined bySR measurements alone if runs in more than one applied field at the same temperature are fit with and as shared parameters. We also present our method of estimating the degree of disorder in the vortex lattice.  相似文献   

3.
We show that ifb andb are two boundary conditions (b.c.) for general spin systems on d such that the difference in the energies of a spin configuration in d is uniformly bounded, |H ,b ()–H ,b()|C < , then any infinite-volume Gibbs states and obtained with these b.c. have the same measure-zero sets. This implies that the decompositions of and into extremal Gibbs states are equivalent (mutually absolutely continuous). In particular, if is extremal,=. Application of this observation yields in an easy way (among other things) (a) the uniqueness of the Gibbs states for one-dimensional systems with forces that are not too long-range; (b) the fact that various b.c. that are natural candidates for producing non-translation-invariant Gibbs states cannot lead to such an extremal Gibbs state in two dimensions.Supported in part by NSF Grant PHY 78–15920 and by the Swiss National Foundation For Scientific Research.  相似文献   

4.
We present a zero magnetic field muon spin rotation study of-O2 (antiferromagnetic phase of solid oxygen) in the temperature range of 10–24 K. Static magnetic order has been observed below the- transition temperatureB =23.8 K. The temperature dependence of the muon precession frequency exhibits behavior characteristic of a two-dimensional Heisenberg spin-1 system with the anisotropy parameter 10–2 quite similar to that of antiferromagnetic phase of the high-temperature superconductor parent compounds. A unique local field at the muon site has been determined to beB 0=1.27(5) kG at low temperatures.  相似文献   

5.
In terms of the Dirac operator P, we introduce on any field a first-order operator D and show that the operator (–) on the spinors (=(n/4(n–1))R; dim W=n) is positive. By means of a universal formula, we show that, on a compact spin manifold of dimension 3, the Hijazi inequality [8] holds for every spinor field such that (P, P) = 2(, ) (=const.). In the limiting case, the manifold admits a Killing spinor which can be evaluated in terms of . Different properties of spin manifolds admitting Killing spinors are proved. D is nothing but the twistor operator.  相似文献   

6.
LetH p =–1/2+V denote a Schrödinger operator, acting inL p v , 1p. We show that (H p )=(H 2) for allp[1, ], for rather general potentialsV.  相似文献   

7.
The energy shift due to the inelastic interaction of the neutron with the time dependent magnetic fields of a gradient radio-frequency spin flipper was studied. A nondispersive perfect crystal spectrometer was used to measure extremly small energy changes of E0.2 eV. The gradient of the magnetic field causes a broadband action of the spin flipper which facilitates its use for new active neutron optical components.  相似文献   

8.
We consider scattering for the equation (+m 2)+3=0 on four-dimensional Minkowski space. Form>0, one-to-one and onto wave operatorsW ± :HH are known to exist for all 0, whereH denotes the Hilbert space of finite-energy Cauchy data. We prove that the maps (,u)W ± (u) and (,u)(W ± )–1 (u) are continuous from [0, )×H toH, and extend to real-analytic functions from an open neighborhood of {0}×H×{0}×H to the Hilbert spaceH –1 of Cauchy data with Poincaré-invariant norm. Form=0, wave operatorsW ± are known to exist as diffeomorphisms ofH for all 0, where hereH denotes the Hilbert space of finite Einstein energy Cauchy data. In this case we prove that the maps (,u)(W ± ) (u) and (,u)(W ± )–1 (u) extend to real-analytic functions from a neighborhood of [0, )×H×H toH.  相似文献   

9.
For a Minkowski spacetime of dimension three, particles of arbitrary, real spin and intermediate (-) statistics, called anyons, are studied within the framework of relativistic quantum field theory. The localization properties of interpolating fields for anyons and the relation between the spin of anyons and their statistics are discussed on general grounds. A model of a quantum field theory exhibiting anyons is described. Our results might be relevant in connection with the fractional quantum Hall effect and two-dimensional models of high-T c superconductors.  相似文献   

10.
The object of the present paper is to study the MHD effects on the laminar flow of a viscous, incompressible and conducting fluid in an annulus with arbitrary time-varying pressure gradient and arbitrary initial velocity in presence of a radial magnetic field. Using finite Hankel transform, solutions for both the unsteady and steady flows under different prescribed pressure gradients have been found out.Notation H a constant characterising the intensity of the magnetic field - p hydrostatic pressure - e magnetic permeability - coefficient of viscosity - kinematic coefficient of voscosity - conductivity of the medium - density - a radius of the inner cylinder - b radius of the outer cylinder - parameter - s positive root - J (sr) Bessel's function of first kind of ordergl - Y (sr) Bessel's function of second kind of order  相似文献   

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