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1.
The paper investigates the modification of the quasiparticle excitation spectrum of type‐II superconductors caused by the
formation of a flux‐line lattice and its effects on the tunnelling rate of light positively charged interstitial particles.
It is shown that near the upper critical field Bc2 the BCS–Gorkov equations predict for the spectral density J(\omega) (giving the probability of an energy exchange \hbar\omega
between particle and the electron system) “superohmic” behaviour \propto \omega3/2 at low frequencies with a prefactor that depends on the position of the tunnelling centre relative to the flux‐line lattice
and on the angle between jump vector and the flux‐lines. As in normal‐conducting metals, at higher frequencies J(\omega)=2Kel\omega, is predicted. At low temperatures T the superohmic J(\omega) leads to hopping rates \nu \propto T-2. At higher temperatures a crossover to the Kondo law (
) is expected.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
R. Orbach 《Hyperfine Interactions》1989,49(1-4):325-333
The excitation dynamics of site diluted magnets can be described at low energies (long length scales) by magnons, and above
a crossover frequency, ωc, (short length scales) by fractons. The density of fracton states is given by
, where
is the fracton dimensionality. Dilution gives rise to a characteristic length ξ∝(p−p
c)ν, wherep
c is the critical concentration for (magnetic) percolation. The crossover frequency ωc is proportional to ξ-1[1+(θ/2)], where θ is the rate at which the diffusion constant decays with distance for diffusion on an equivalent network. A fractal
dimensionD describes the density of magnetic sites on the infinite network, and
. For percolating networks,
for all dimensions ≥2. Neutron scattering structure factor measurements by Uemura and Birgeneau compare well with calculations
using fracton concepts.
Magnons are extended at low energies, while the fracton states are geometrically localized, with a wave function envelope
proportional to exp
. Here,
is the fracton length scale at frequency ω. The exponentd
ϕ lies between 1 andd
min, the chemical length index (of the order of 1.6 in three dimensions). The localization of the magnetic excitations causes
a spread in the NMR relaxation rates. A given nuclear moment will experience only a limited set of fracton excitations, resulting
in an overall non-exponential decay of the NMR relaxation signal. When strong cross-relaxation is present, the relaxation
will be exponential, but the temperature dependence will be strongly altered from the concentrated result. 相似文献
3.
An ellipticaliy polarized field applied to a physical system and related responses are very common in physics. Due to the loss of symmetry, the response problems are very difficult to solve, and are usually described by nonlinear and unseparable equations. By introducing a time transformation=(1/)tan–1(r tant), wherer is the ratio between the two components, one may reset the symmetry of the field. The equation
相似文献
4.
We consider one-dimensional (1D) interacting spinless fermions with a non-linear spectrum in a clean quantum wire (non-linear
bosonization). We compute diagrammatically the 1D dynamical structure factor, S(ω,q), beyond the Tomonaga approximation focusing
on it's tails, |ω| ≫vq,
i.e. the 2-pair excitation continuum due to forward scattering. Our methodology reveals three classes of diagrams: two “chiral”
classes which bring divergent contributions in the limits ω→±vq, i.e. near the single-pair excitation continuum, and a “mixed”
class (so-called Aslamasov-Larkin or Altshuler-Shklovskii type diagrams) which is crucial for the f-sum rule to be satisfied.
We relate our approach to the T=0 ones present in the literature. We also consider the
case and show that the 2-pair excitation continuum dominates the single-pair one in the range: |q|T/kF ≪ω±vq ≪T (substantial for q ≪kF). As applications we first derive the small-momentum optical conductivity due to forward scattering: σ∼1/ω for T ≪ω and σ∼T/ω2 for T ≫ω. Next, within the 2-pair excitation continuum, we show that the attenuation rate of a coherent mode of dispersion
Ωq crosses over from
, e.g. γq ∼|q|3 for an acoustic mode, to
, independent of Ωq, as temperature increases. Finally, we show that the 2-pair excitation continuum yields subleading curvature corrections
to the electron-electron scattering rate:
, where V is the dimensionless strength of the interaction. 相似文献
5.
Dalitz decays of ω and ρ mesons,
and
, produced in pp collisions are calculated within a covariant effective meson-nucleon theory. We argue that the ω transition form factor
is experimentally accessible in a fairly model-independent way in the reaction pp → ppπ0
e
+
e
- for invariant masses of the π0
e
+
e
- subsystem near the ω pole. Numerical results are presented for the intermediate-energy kinematics of envisaged HADES experiments. 相似文献
6.
William Arveson 《Communications in Mathematical Physics》2009,286(1):283-312
We show that states on tensor products of matrix algebras whose ranks are relatively small are almost surely entangled, but that states of maximum rank are not. More precisely, let and be full matrix algebras with m ≥ n, fix an arbitrary state ω of N, and let E(ω) be the set of all states of that extend ω. The space E(ω) contains states of rank r for every r = 1, 2, . . . , m · rank ω, and it has a filtration into compact subspaces
7.
8.
D. M. Kagan M. V. Feigel’man L. B. Ioffe 《Journal of Experimental and Theoretical Physics》1999,89(4):781-787
We show that the ground state of a periodic long-range Josephson array frustrated by a magnetic field is a glass for sufficiently
large Josephson energies despite the absence of quenched disorder. Like superconductors, this glass state has non-zero phase
stiffness and Meissner response; for lower Josephson energies the glass “melts” and the ground state loses its phase stiffness
and becomes insulating. We find the critical scaling behavior near this quantum phase transition: the excitation gap vanishes
as (J−J
c
)2, and the frequency-dependent magnetic susceptibility behaves as
.
Zh. éksp. Teor. Fiz. 116, 1450–1461 (October 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
9.
Guido A. Raggio 《Letters in Mathematical Physics》1982,6(3):233-236
It is shown that for normal states ρ and φ of a W
*-algebra
, where P(.,.) is the transition probability considered by Uhlmann [1], and ζ(ω) is the vector in the natural positive cone of some
standard faithful representation of A, associated with the normal state ω. The above inequality is equivalent to:
, where d(.,.) is the Bures distance function [5]. 相似文献
10.
We examine the thermal conductivity and bulk viscosity of a one-dimensional (1D) chain of particles with cubic-plus-quartic
interparticle potentials and no on-site potentials. This system is equivalent to the FPU-α
β system in a subset of its parameter space. We identify three distinct frequency regimes which we call the hydrodynamic regime, the perturbative regime and the collisionless regime. In the lowest frequency regime (the hydrodynamic regime) heat is transported ballistically by long wavelength sound modes.
The model that we use to describe this behaviour predicts that as ω→0 the frequency dependent bulk viscosity,
, and the frequency dependent thermal conductivity,
, should diverge with the same power law dependence on ω. Thus, we can define the bulk Prandtl number,
, where m is the particle mass and k
B
is Boltzmann’s constant. This dimensionless ratio should approach a constant value as ω→0. We use mode-coupling theory to predict the ω→0 limit of Pr
ζ
. Values of Pr
ζ
obtained from simulations are in agreement with these predictions over a wide range of system parameters. In the middle frequency
regime, which we call the perturbative regime, heat is transported by sound modes which are damped by four-phonon processes. This regime is characterized by an intermediate-frequency
plateau in the value of
. We find that the value of
in this plateau region is proportional to T
−2 where T is the temperature; this is in agreement with the expected result of a four-phonon Boltzmann-Peierls equation calculation.
The Boltzmann-Peierls approach fails, however, to give a nonvanishing bulk viscosity for all FPU-α
β chains. We call the highest frequency regime the collisionless regime since at these frequencies the observing times are much shorter than the characteristic relaxation times of phonons. 相似文献
11.
Using 160GeV muon scattering data collected with the COMPASS experiment at CERN, the exclusive production of ωπ0 via virtual photons was studied. Selective population of a peak around 1250MeV is observed. Possible contributions from spin-parity
1- are searched for, inspecting decay angular correlations. In particular, the orientation of the ω decay plane may allow a
distinction from the 1+
b
1(1235) state. Our observation is compared with indications of a (1250) in annihilation and in γp .
Original article based on material presented at HADRON 2007. 相似文献
12.
For the 2D Navier--Stokes equation perturbed by a random force of a suitable kind we show that, if g(F) is an arbitrary real continuous function with (at most) polynomial growth, then the stationary in time vorticity field (t,x) satisfies
where M_1 is a number, independent of g, which measures the strength of the random forcing. Another way of stating this result is that, in the unique stationary measure of this system, the random variables g((t,x) and |(t,x)|2 are uncorrelated for each t and each x.This revised version was published online in March 2005 with corrections to the page numbers. 相似文献
13.
14.
Avinash Khare 《Letters in Mathematical Physics》1979,3(6):475-480
Static finite energy solutions of the field theory described by
are obtained. Some of the interesting features of this model are (1) the mass-square here is positive unlike in the λφ4 Higg's model, (2) the potential has three global minimas, (3) the spectrum is bounded from below unlike in the λφ4 theory with λ<0, (4) there are two kink and two antikink solutions, (5) unlike sine-Gordon and λφ4 models here there are two particles with masses m and 2m. Nontopological finite energy solutions have also been obtained for gφ
6 field theory with g < 3λ
2 / 16m
2. 相似文献
15.
F. P. Heßberger S. Hofmann D. Ackermann S. Antalic B. Kindler I. Kojouharov P. Kuusiniemi M. Leino B. Lommel R. Mann K. Nishio A. G. Popeko B. Sulignano S. Saro B. Streicher M. Venhart A. V. Yeremin 《The European Physical Journal A - Hadrons and Nuclei》2006,30(3):561-569
The decay of the isotopes 255Rf, 251No and 247Fm produced in the reactions
, and
was investigated by means of α-γ spectroscopy. Previously observed γ transitions in coincidence with α decays of 255Rf were confirmed, their energies and line intensities were measured more precisely, and their multipolarities were determined
as E1. In 251No a new isomeric state at E
* > 1700keV with a half-life of ≈ 2μs was identified. The decay of 247Fm was measured more precisely. A partial level scheme of the daughter nucleus 243Cf could be established. 相似文献
16.
17.
R. Meier D. Kruk A. Bourdick E. Schneider E. A. Rössler 《Applied magnetic resonance》2013,44(1-2):153-168
Field cycling 1H nuclear magnetic resonance (NMR) relaxometry is applied to study rotational as well as translational dynamics in molecular liquids. The measured relaxation rates, $ T_{1}^{ - 1} \left( \omega \right) \equiv R_{1} \left( \omega \right) $ , contain intra- and intermolecular contributions, $ R_{{1,{\text{intra}}}}^{{}} \left( \omega \right) $ and $ R_{{ 1 , {\text{inter}}}}^{{}} \left( \omega \right) $ . The intramolecular part is mediated by rotational dynamics, the intermolecular part by translation as well as rotation. The rotational impact on the intermolecular relaxation (eccentricity effect) is due to the spins not located in the molecule’s center. The overall relaxation rate is decomposed into $ R_{{1,{\text{intra}}}}^{{}} \left( \omega \right) $ and $ R_{{ 1 , {\text{inter}}}}^{{}} \left( \omega \right) $ by isotope dilution experiments. It is shown that the eccentricity model (Ayant et al. in J. Phys. (Paris) 38:325, 1977) reproduces fairly well the bimodal shape of $ R_{{ 1 , {\text{inter}}}}^{{}} \left( \omega \right) $ for o-terphenyl and glycerol. As the relaxation contribution associated with translational dynamics dominates at lower frequencies, the overall relaxation rate shows a universal linear behavior when plotted versus square root of frequency. This allows determining the self-diffusion coefficient, D, in a model-independent way. It is demonstrated that the shape of NMR master curves comprising relaxation data for different temperatures, linked by frequency–temperature superposition, reflects the relative strength of translational and rotational contributions. 相似文献
18.
Recently performed high resolution incoherent neutron scattering experiments on liquid sodium at smallA and low make the precise evaluation of the frequency distribution of the liquid feasible. An appropriate extension of the well known Egelstaff formula
for the evaluation of the frequency distribution in a liquid is deduced. The new analysis is shown to be exact in the smallQ low region, removing the singularity of the above formula at 0 andQ0. The easy applicability of the evaluation is demonstrated on neutron scattering data of liquid sodium, where the long discussed low frequency cusp ofz() could be revealed. 相似文献
19.
N. M. Agababyan V. V. Ammosov M. Atayan N. Grigoryan H. Gulkanyan A. A. Ivanilov Zh. Karamyan V. A. Korotkov 《Physics of Atomic Nuclei》2006,69(1):35-38
The influence of nuclear effects on the production of neutral strange particles (V
0) is investigated using the data obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam (with E
v
=3−30 GeV) at the Serpukhov accelerator. The mean multiplicity of V
0 particles in nuclear interactions,
, is found to exceed significantly that in “quasideuteron” interactions,
. The ratio of
is larger than that for π− mesons,
. It is shown that the multiplicity gain of V
0 particles can be explained by intranuclear interactions of produced pions.
The text was submitted by the authors in English. 相似文献
20.
Infrared asymptotic behavior of a scalar field, passively advected by a random shear flow, is studied by means of the field
theoretic renormalization group and the operator product expansion. The advecting velocity is Gaussian, white in time, with
correlation function of the form μ d(t-t¢) / k^d-1+x\propto\delta(t-t') / k_{\bot}^{d-1+\xi}, where k
⊥=|k
⊥| and k
⊥ is the component of the wave vector, perpendicular to the distinguished direction (‘direction of the flow’)—the d-dimensional generalization of the ensemble introduced by Avellaneda and Majda (Commun. Math. Phys. 131:381, 1990). The structure functions of the scalar field in the infrared range exhibit scaling behavior with exactly known critical
dimensions. It is strongly anisotropic in the sense that the dimensions related to the directions parallel and perpendicular
to the flow are essentially different. In contrast to the isotropic Kraichnan’s rapid-change model, the structure functions
show no anomalous (multi)scaling and have finite limits when the integral turbulence scale tends to infinity. On the contrary,
the dependence of the internal scale (or diffusivity coefficient) persists in the infrared range. Generalization to the velocity
field with a finite correlation time is also obtained. Depending on the relation between the exponents in the energy spectrum
E μ k^1-e\mathcal{E} \propto k_{\bot}^{1-\varepsilon} and in the dispersion law w μ k^2-h\omega\propto k_{\bot}^{2-\eta}, the infrared behavior of the model is given by the limits of vanishing or infinite correlation time, with the crossover
at the ray η=0, ε>0 in the ε–η plane. The physical (Kolmogorov) point ε=8/3, η=4/3 lies inside the domain of stability of the rapid-change regime; there is no crossover line going through this point. 相似文献
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