共查询到20条相似文献,搜索用时 31 毫秒
1.
H. Albrecht H. Meierling E. F. Wassermann H. Zähres F. T. Hedgcock 《Zeitschrift für Physik B Condensed Matter》1982,49(3):213-220
The impurity contribution to the resistivity in zero field (T) of dilute hexagonal single crystals of ZnMn, CdMn and MgMn has been studied in the mK range on samples cut parallel () and perpendicular () to thec-axis, using a SQUID technique for the measurements. Typical spin glass behavior is found in (T) as well as (T) for all alloys, with Kondo like logarithmic increases at higher temperatures and maxima atT
m at lower temperatures, indicating the influence of impurity interactions. The differences in the corresponding isotropic resistivity poly(T) between the three systems can qualitatively be understood within the framework of a theoretical model by Larsen, describing (T) as a function of universal quantitiesT/T
K and RKKY/T
K
, where RKKY is the RKKY-interaction strength andT
K the Kondo temperature. With respect to the two lattice directions studied, the behavior of (T and (T is anisotropic in the Kondo regime as well as in the range where ordering becomes important. While the anisotropy in the Kondo slope can be understood by an anisotropic unitarity limit, the understanding of the anisotropy in region where impurity interactions are important remains problematic.Dedicated to Prof. Dr. S. Methfessel on the occasion of his 60th birthday 相似文献
2.
We review some exact results for the motion of a tagged particle in simple models. Then, we study the density dependence of the self-diffusion coefficientD
N() in lattice systems with simple symmetric exclusion in which the particles can jump, with equal rates, to a set ofN neighboring sites. We obtain positive upper and lower bounds onF
N()=N{(1–)–[DN()/DN(0)]}/[(1–)]x for [0, 1]. Computer simulations for the square, triangular, and one-dimensional lattices suggest thatF
N becomes effectively independent ofN forN20. 相似文献
3.
Let be an action of a compact abelian groupG on aC*-algebraA, and assume that the fixed-point subalgebraA
is an AF-algebra. We show that if is a closed *-derivation onA commuting with , and the restriction of toA
generates a one-parameter group of *-automorphisms, then itself is a generator. In particular, the result applies if is an infinite product action ofG on a UHF algebra. Furthermore, if in this situation 1 and 2 are two derivations both satisfying the hypotheses on , and 1 and 2 have the same restriction toA
, then there exists a one-parameter subgroup of the action with generator 0 such thatD(1)D(2)D(0) is a joint core for the three derivations, and 2=1+0 on this core. 相似文献
4.
Renormalized transport equations for general Fokker-Planck systems are derived and applied to the bistable potential model. The exact equation for the expectation value x
t
can be evaluated in both domains Dx
± and xD
0 outside and between the potential minima, leading to drastic differences of the dynamics prevailing inD
± andD
0, respectively. 相似文献
5.
For one-dimensional expanding mapsT with an invariant measure we consider, in a parameter space, the envelope
n
of the real lines associated to any couple of points of the orbit, connected byn iterations ofT. If the map hass inverses and is piecewise linear, then the sets
n
are just the union ofs
n
points and converge to the invariant Cantor set ofT. A correspondence between all the sets and their measures is established and allows one to associate the atomic measure on 1 to the completly continuous measure on the Cantor set. If the map is nonlinear, hyperbolic, and hass inverses, the sets
n
are homeomorphic to the Cantor set; they converge to the Cantor set ofT and their measures converge to the measure of the Cantor set whenn. The correspondence between the sets
n
allows one to define converging approximation schemes for the map an its measure: one replaces each of thes
n
disjoint sets with a point in a convenient neighborhood and a probability equal to its measure and transforms it back to the original set 1. All the approximations with linear Cantor systems previously proposed are recovered, the converging proprties being straightforward in the present scheme. Moreover, extensions to higher dimensionality and to nondisconnected repellers arte possible and are briefly examined. 相似文献
6.
Alan D. Sokal 《Communications in Mathematical Physics》1982,86(3):327-336
I use Israel's methods to prove new theorems of ubiquitous pathology for classical and quantum lattice systems. The main result is the following: Let be any interaction and be any translation-invariant equilibrium state for (extremal or not). Then there exists a sequence {
k
} of interactions converging to , having extremal (or even unique) translation-invariant equilibrium states
k
, such that {
k
} converges to . In certain situations the perturbations
k
– can be chosen to lie in a cone of antiferromagnetic pair interactions. I discuss the connection with results of Daniëls and van Enter, and point out an application to the one-dimensional ferromagnetic Ising model with 1/r
2 interaction (Thouless effect). 相似文献
7.
Alan D. Sokal 《Journal of statistical physics》1981,25(1):25-50
A variety of rigorous inequalities for critical exponents is proved. Most notable is the low-temperature Josephson inequalitydv +2 2–. Others are 1 1 +v, 1 1
, 1,d 1 + 1/ (for d),dv, 3 + (for d), 4 , and 2m 2m+2 (form 2). The hypotheses vary; all inequalities are true for the spin-1/2 Ising model with nearest-neighbor ferromagnetic pair interactions.NSF Predoctoral Fellow (1976–1979). Research supported in part by NSF Grant PHY 78-23952. 相似文献
8.
G. Rideau 《Letters in Mathematical Physics》1984,8(5):421-433
Let U(a, ) be a representation of the Poincaré group with mass and helicity zero, realized in the space of C
-functions with compact support on 3, without the origin. Let U
(2)(a, ) denote the tensorial product of U(a, ) by itself. We explicitly determine the cocycles of extension of U(a, ) by U
(2)(a, ) and we prove that the nontrivial cohomology is indexed by (u(),),u()D
1
]0,3\,. 相似文献
9.
Multiparticle fractal aggregation 总被引:1,自引:0,他引:1
Richard F. Voss 《Journal of statistical physics》1984,36(5-6):861-872
Kinetic fractal aggregation in a particle bath where a fractionf of the sites are initially occupied is studied withd=2 computer simulations. Independent particles diffusing to a fixed cluster produce an aggregate with fractal dimensionD 1.7 up to a correlation length(f). At larger lengthsD2.(f) asf 0. When the particles remain fixed but the cluster undergoes a rigid random walkD appears constant at larger scales but varies withf. D 1.95 at largef andD 1.7 asf 0. In both cases, the aggregate sizeN(t) grows with timet
(f)
. Aggregation on a surface by independently diffusing particles produces shapes reminiscent of electrochemical dendritic growth. The dependence of growth rate and geometry is studied as a function of particle concentration and sticking probability. 相似文献
10.
We consider the grand canonical partition function for the ordered one-dimensional, two-component plasma at fugacity in an applied electric fieldE with Dirichlet boundary conditions. The system has a phase transition from a low-coupling phase with equally spaced particles to a high-coupling phase with particles clustered into dipolar pairs. An exact expression for the partition function is developed. In zero applied field the zeros in the plane occupy the imaginary axis from –i to –ic and ic to i for some c. They also occupy the diamond shape of four straight lines from ±ic to c and from ±ic to –c. The fugacity acts like a temperature or coupling variable. The symmetry-breaking field is the applied electric fieldE. A finite-size scaling representation for the partition in scaled coupling and scaled electric field is developed. It has standard mean field form. When the scaled coupling is real, the zeros in the scaled field lie on the imaginary axis and pinch the real scaled field axis as the scaled coupling increases. The scaled partition function considered as a function of two complex variables, scaled coupling and scaled field, has zeros on a two-dimensional surface in a domain of four real variables. A numerical discussion of some of the properties of this surface is presented. 相似文献
11.
K. H. Fischer 《Zeitschrift für Physik B Condensed Matter》1984,55(4):317-324
The dynamics of ann-component vector spin glass with infinite range interactions are investigated near and above the Gabay-Toulouse (GT) line. The local transverse susceptibility
T
for 0 varies along the whole GT lineT
c1
(H) as
v
, with a field and temperature independent critical exponentv=1/2. The longitudinal susceptibility
L
() remains analytic for all (T, H)T
c1
(H), except for a cross-over fromv=1 tov=1/2 forH0 at the freezing temperatureT=T
f
. The dynamic susceptibilities
T
() and
L
() are already coupled above the GT line via self-energy terms. BelowT
c1
(H), this coupling is strongly enhanced by other mechanisms. 相似文献
12.
K. Kriŝtiaková O. Ŝauŝa J. Kriŝtiak Ŝ. Jánoŝ 《Zeitschrift für Physik B Condensed Matter》1989,75(2):197-199
We have measured the ac susceptibility of a wire with a Nb core (1.27 mm diam.) and a Cu cladding (0.37 mm thickness) atT50 K andB0.1 mG. Due to its proximity to Nb, the Cu becomes fully superconducting. From the data we find a breakdown fieldH
b
=1.2 (mG) and a coherence length =2.2T
–1/2 (m) for the Cu, as well as a field penetration depth -34T
1/2 (m) at the Cu/Nb interface. 相似文献
13.
Joel L. Lebowitz 《Journal of statistical physics》1977,16(1):3-9
In a recent note Barber showed, for a spin-1/2 Ising system with ferromagnetic pair interactions, that some critical exponents of the triplet order parameter
i
j
k
are the same as those of the magnetization
i
. Here we prove such results for all odd correlations and dispense with the requirement of pair interactions. We also prove that the critical temperatureT
c
, defined as the temperature below which there is a spontaneous magnetization, is for fixed even spin interactionsJ
e
independent of the way in which the odd interactionsJ
o
approach zero from above. This is achieved by using only the simplest, Griffiths-Kelley-Sherman (GKS), inequalities, which apply to the most general many-spin, ferromagnetic interactions.Research supported in part by NSF Grant #MPS 75-20638. 相似文献
14.
R. M. Nugayev 《International Journal of Theoretical Physics》1987,26(5):407-428
Particle creation by a black hole is described in terms of temperature corrections to the Casimir effect. The results of Levin, Polevoy, and Ritov for spectral and total Poynting vector for a fluctuating electromagnetic field in a plane vacuum gap between two arbitrary media with different temperatures in flat spacetime are applied to clarify the situation that exists between the horizon of a nonrotating black hole and spatial infinity. This helps to reveal the mechanism of particle creation. The Hawking radiation is born inside the bell formed by a potential barrier of a black hole in all the region [2M, ]. Its blackbody spectrum is due to the interaction of field fluctuations with the surface of the bell. The particles between the walls are virtual ones. They can become real after passing through the [3M, ] tail, appearing to an observer at future infinityJ
+ as real ones. The arguments for and against the present standpoint are discussed. 相似文献
15.
A cluster of two atoms described by thes-f model with Coulomb repulsion has been considered. The interaction between localized 4f electrons (S=1/2) is taken in the molecular field approximation. The thermodynamic quantities like magnetization, specific heat and correlation functions n
, n
, S
z
n
, S
z
n
, S
z (n
–n
), n
n
and S
+
a
+
a
as functions of temperature are presented for different band fillingN=0, 0.5, 1, 1.5, 2. The dependence of Curie temperature onN is calculated. The phase diagram forN=1 (T=0K) shows the possibility of existence of two phases: paramagnetic and ferromagnetic.The Curie temperature and the specific heat as functions ofN exhibit similar trends as found in experiments on doped magnetic semiconductors. 相似文献
16.
We have proposed that the cosmic ray spectrum knee, the steepening of the cosmic ray spectrum at energy E 1015.5 eV, is due to new physics, namely new interactions at TeV cm energies which produce particles undetected by the experimental apparatus. In this letter we examine specifically the possibility that this interaction is low scale gravity. We consider that the graviton propagates, besides the usual four dimensions, into an additional , compactified, large dimensions and we estimate the graviton production in pp collisions in the high energy approximation where graviton emission is factorized. We find that the cross section for graviton production rises as fast as (
/M
f)2+, where M
f is the fundamental scale of gravity in 4 + dimensions, and that the distribution of radiating a fraction y of the initial particle's energy into gravitational energy (which goes undetected) behaves as y
– 1. The missing energy leads to an underestimate of the true energy and generates a break in the inferred cosmic ray spectrum (the knee). By fitting the cosmic ray spectrum data we deduce that the favorite values for the parameters of the theory are M
f
8 TeV and = 4. 相似文献
17.
A recent calculation, in the weak-noise limit, of the rate of escape of a particle over a one-dimensional potential barrier is extended by including an inertial term in the Langevin equation. Specifically, we consider a system described by the Langevin equation
, where is a Gaussian colored noise with mean zero and correlator (t)(t')=(D/)exp(–|t–t'|/). A pathintegral formulation is augmented by a steepest descent calculation valid in the weak-noise (D0) limit. This yields an escape rateexp(–S/D), where the actionS is the minimum, over paths characterizing escape over the barrier, of a generalized Onsager-Machlup functional, the extremal path being an instanton of the theory. The extremal actionS is calculated analytically for smallm and for general potentials, and numerical results forS are displayed for various ranges ofm and for the typical case of the quartic potentialV(x)=–x
2/2+x
4/4. 相似文献
18.
Z. Haba 《Letters in Mathematical Physics》1996,37(2):223-231
Let
t
be an analytic solution of the Schrödinger equation with the initial condition . Let
t
be the solution of the Schrödinger equation with the initial condition =, where is an analytic function. When 0, then
t
(x)
t
(x)1 (
t
(x)), where
t
(x) trajectory starting from x. We relate this result to Feynman's sum over trajectories and complex stochastic differential equations. 相似文献
19.
Let {X
t:0} denote random walk in the random waiting time model, i.e., simple random walk with jump ratew
–1(X
t), where {w(x):xd} is an i.i.d. random field. We show that (under some mild conditions) theintermediate scattering function
F(q,t)=E
0
(qd) is completely monotonic int (E
0 denotes double expectation w.r.t. walk and field). We also show that thedynamic structure factor
S(q, w)=2
0
cos(t)F(q, t) exists for 0 and is strictly positive. Ind=1, 2 it diverges as 1/||1/2, resp. –ln(||), in the limit 0; ind3 its limit value is strictly larger than expected from hydrodynamics. This and further results support the conclusion that the hydrodynamic region is limited to smallq and small such that ||D |q|2, whereD is the diffusion constant. 相似文献
20.
We extend the bichromatic majority model by including (one-dimensional isotropic) correlations and numerically discuss, through Monte Carlo simulations, the simple, 1/3, and 2/3 majority rules. We calculate, as functions of the concentration and correlation degree, the mean finite cluster size, and the order parameterm as well as their respective critical exponents and. We find1 regardless of the correlation degree or the type of majority. Also, a supplementary divergence of is observed at the>0 borderline. 相似文献