共查询到20条相似文献,搜索用时 31 毫秒
1.
Electromagnetic effects are believed to play an important role in ferromagnetic superconductors (FMS). As an, to date, unobserved consequence of the electromagnetic coupling of the superconducting and the magnetic order parameter, we predict the possibility of Lifshitz point critical behaviour in FMS. In particular we present a detailed mean field investigation of the (T, x)-phase diagram of Er1?xHoxRh4B4 in the neighbourhood of the “modified Lifshitz point”, which separates the normal paramagnetic, the superconducting paramagnetic and the normal ferromagnetic phases. 相似文献
2.
A. Zumsteg M. Ziegler Prof. Dr. W. Känzig M. Bösch 《Zeitschrift für Physik B Condensed Matter》1974,17(4):267-291
The phase transitions of Alkali-Hyperoxide crystals (NaO2, KO2, RbO2, and CsO2) grown in liquid ammonia have been investigated by means of the following measurements:
- magnetic susceptibility
- differential magnetic susceptibility as magnetic field
- magnetization curve in static and pulsed fields
- specific heat.
3.
J. L. van Hemmen A. C. D. van Enter J. Canisius 《Zeitschrift für Physik B Condensed Matter》1983,50(4):311-336
A simple, exactly soluble, model of a spin-glass with weakly correlated disorder is presented. It includes both randomness and frustration, but its solution can be obtained without replicas. As the temperatureT is lowered, the spin-glass phase is reached via an equilibrium phase transition atT=T f . The spin-glass magnetization exhibits a distinctS-shape character, which is indicative of a field-induced transition to a state of higher magnetization above a certain threshold field. For suitable probability distributions of the exchange interactions.
- A mixed phase is found where spin-glass and ferromagnetism coexist.
- The zero-field susceptibility has a flat plateau for 0≦T≦T f and a Curie-Weiss behaviour forT>T f .
- At low temperatures the magnetic specific heat is linearly dependent on the temperature.
4.
Theq states Potts model exhibits a first order phase transition at some inverse temperature β t between “ordered” and “disordered” phases forq large as proved in [1]. In space dimension 2 we use theduality transformation as aninternal symmetry of the partition function at β t to derive an estimate on the probability of a contour. This enables us to prove the preceding result and the following new results:
- The discontinuity of the mass gap at β t .
- The existence of astrictly positive surface tension between two ordered phases up to β t .
- The existence of a non-zero surface tension between an “ordered” and the “disordered” phase at β t .
5.
A. Jánosi 《Zeitschrift für Physik B Condensed Matter》1990,80(3):393-400
We study the effects of some of the most important and typical structural changes in two-phase systems on selected structural parameters obtained from small-angle x-ray scattering (SAXS) measurements. To limit the present study, it was assumed that the Phase, 1, embedded in the matrix
- is monodispersed and homogeneous,
- possesses one of the three most extreme shapes (spherical, fibrillar or lamellar) and
- changes its behaviour
- through type change (spinodal or nucleotic or coarsening), without changing the shape,
- through a change of the shape only, or
- through a) (type change) and b) (shape change) simultaneously.
- chord lengthl 1 (and/or radius of gyrationR),
- volume partw 1 of the Phase 1, and
- relative inner surfaceS v of the system.
- spinodal change, all three SAXRS parameters are increasing or decreasing simultaneously and proportional to a power of the intensity of the change,
- nucleotic change,l 1 (and/orR) is unchanged, the other two (w 1 andS v ) are increasing or decreasing simultaneously and directly proportional to the intensity,
- coarsening change,w 1 is unchanged and anincreasing ofl 1 is always accompanied by adecreasing ofS v and vice versa.
6.
The creation and propagation of jump discontinuities in the solutions of semilinear strictly hyperbolic systems is studied in the case where the initial data has a discrete set, {x i } i =1n , of jump discontinuities. LetS be the smallest closed set which satisfies:
- S is a union of forward characteristics.
- S contains all the forward characteristics from the points {x i } i =1n .
- if two forward characteristics inS intersect, then all forward characteristics from the point of intersection lie inS.
7.
《Solid State Communications》1986,57(8):707-709
The spatial anisotropy of critical fluctuations has strong influence on the temperature dependence of the elastic constants of an elastic medium coupled magneto- or electrostrictive to the order parameter. Under pinned boundary conditions we find for uniaxial dipolar systems of hexagonal and trigonal symmetry a second order phase transition, where only c11 and c12 show critical behaviour. For other symmetries a first order transition is expected. At an uniaxial Lifshitz point only c33 becomes critical and the phase transition remains of second order for any symmetry. 相似文献
8.
Notker Rösch 《Zeitschrift für Physik A Hadrons and Nuclei》1968,215(4):368-376
We use the molecular model of low energy fission, which describes the nucleus by two interacting fragments, to calculate the moment of inertia for U236 in the cranking approximation including BCS theory. We show that the moment of inertia at the saddle point:
- depends almost linearly on the fragment distance.
- is influenced only very weakly by the pairing constant and by the fragment deformations.
- shows, as a function of the distribution of mass between the two fragments (A 1 ,A 2 ), a minimum near the magic configurationA 1=132,Z 1=50 and depends in this mass region strongly on the term structure near the Fermi energy.
- is approximately that of a rigid body.
9.
The critical properties of an XY helimagnet on a square lattice with two chiral order parameters are studied by Monte Carlo simulations. This model is a modification of the J 1-J 2-J 3 model with J 2 = 0. The case of different third range order interactions J 3 are considered, J 3 a ?? J 3 b . A first order transition is found away from the Lifshitz points 4J 3 a = J 1 and 4 J 3 b = J 1. It is pointed out that a chiral spin liquid phase possibly exists near the Lifshitz points. 相似文献
10.
G. Müller 《Zeitschrift für Physik B Condensed Matter》1987,68(2-3):149-159
The present study highlights some of the complexities observed in the dynamical properties of one-dimensional quantum spin systems. Exact results for zero-temperature dynamic correlation functions are presented for two contrasting situations:
- a system with a fully ordered ferromagnetic ground state;
- a system at aT c=0 critical point.
11.
The frequency behaviour of axial modes was investigated during the initial phase of mode competition in case of a helical TEA-CO2 laser. With the help of a homodyne technique single-shot and multi-shot beat spectra were measured. Analysing these under various aspects and combining the results of an earlier investigation it was found that
- inferior modes exist only for 100–200 ns.
- their spectral width is less than 1 MHz and is determined by lifetime broadening, with the dominant mode narrower than 0.77 MHz,
- in the average over many shots the spectral envelope of modes does not follow a Lorentzian shape as expected for the Lorentzian gain curve,
- the beat powers change widely from shot to shot, whereas the total laser power remains constant,
- no specific phase structures are likely to govern the laser emission, although the maximum emission principle appears to be obeyed with every individual shot. In an appendix relations are derived and summarized which are required for the evaluation of beat mode spectra and for the determination of line width as they apply to the actual time dependence of the laser emission.
12.
E. Mourre 《Communications in Mathematical Physics》1981,78(3):391-408
We give a sufficient condition for a self-adjoint operator to have the following properties in a neighborhood of a pointE of its spectrum:
- its point spectrum is finite;
- its singular continuous spectrum is empty;
- its resolvent satisfies a class of a priori estimates.
13.
J. C. M. Henning J. H. den Boef 《Applied Physics A: Materials Science & Processing》1978,16(4):353-357
A novel method for measuring magnetostriction constants is presented. A strain, periodic in time, applied to the sample, causes a modulation of the ferromagnetic resonance line position. The height of the signal obtained after phase-sensitive detection is proportional to the strain modulation depth. The appropriate magnetostriction constant λ is obtained by comparing the height of the SMFMR signal with that of the FMR line, as recorded by means of magnetic field modulation. Features of the new technique are:
- high sensitivity: λmin? 10?9 forM=100 Oe and linewidth ΔH d=1 Oe;
- λ's belonging to distinct precession modes are separately determined;
- applicable to thin layers for which strain gauge techniques cannot be used;
- wide temperature range: 1.2 K<T<300 K;
- uniform stress.
14.
Inequalities on eigenvalues of the Schrödinger operator are re-examined in the case of spherically symmetric potentials. In particular, we obtain:
- A connection between the moments of order (n ? 1)/2 of the eigenvalues of a one-dimensional problem and the total number of bound statesN n, inn space dimensions;
- optimal bounds on the total number of bound states below a given energy in one dimension;
- alower bound onN 2;
- a self-contained proof of the inequality for α ≧ 0,n ≧ 3, leading to the optimalC 04,C 3;
- solutions of non-linear variation equations which lead, forn ≧ 7, to counter examples to the conjecture thatC 0n is given either by the one-bound state case or by the classic limit; at the same time a conjecture on the nodal structure of the wave functions is disproved.
15.
Francesco Pegoraro 《Communications in Mathematical Physics》1975,42(1):41-63
We consider a theorem due to Michel [1] which relates the invariance properties in peculiar directions in a linear space on which we represent a Lie groupG to the extremal points of an arbitrary smoothG-invariant function. The group we are interested in isSO(4) and we apply the mathematical results to the following problems:
- mixed linear Stark Zeeman effect in a hydrogen atom,
- perturbation of a finite Robertson-Walker metric,
- gas evolutions preserving angular momentum and vorticity.
16.
P. Steiner V. Kinsinger I. Sander B. Siegwart S. Hüfner C. Politis 《Zeitschrift für Physik B Condensed Matter》1987,67(1):19-23
XPS and UPS photoemission experiments on the highT c superconductors (T c ≈90 K) with nominal composition YBa2Cu3O9-y (y≈2) show the following:
- The density of electronic states at the Fermi energy is very small, much smaller than in pure Cu.
- The Cu 2p spectra show only a Cu2+ contribution.
- The Ba core levels show a structure with two components of nearly equal magnitude, which leads to the suggestion that these compounds have large O2? vacancies coordinated to Ba2+ sites.
- Annealing at 400°C under UHV conditions leads possibly to a partial reduction of Cu2+ to lower Cu valence states and to a small increase of the O2? vacancy component of the Ba2+ line.
17.
The formalism developed in a previous paper is applied to yield a phase cell cluster expansion for a hierarchical ø 3 4 model. The field is expanded into modes with specific renormalization group scaling properties. The present cluster expansion for a vacuum expectation value is formally the natural factorization of each term in the perturbation expansion into the contribution of modes connected to the variables in the expectation via interactions, and that of the complementary set. The expectation value is thus realized as a sum of contributions due tofinite subsets of the modes. We emphasize the following additional features:
- Partitions of unity are not used.
- There areessentially no cut-offs.
- The expansion is developed directly, without an initial need to prove an ultraviolet stability bound, the most difficult part of the traditional approach.
18.
M. Yu. Kagan V. V. Val’kov V. A. Mitskan M. M. Korovuskin 《Journal of Experimental and Theoretical Physics》2013,117(4):728-741
Using the Shubin-Vonsovsky model in the weak-coupling regime W > U > V (W is the bandwidth, U is the Hubbard onsite repulsion, and V is the Coulomb interaction at neighboring sites) based on the Kohn-Luttinger mechanism, we determined the regions of the existence of the superconducting phases with the d xy , p, s, and $d_{x^2 - y^2 } $ symmetry types of the order parameter. It is shown that the effective interaction in the Cooper channel considerably depends not only on single-site but also on intersite Coulomb correlations. This is demonstrated by the example of the qualitative change and complication of the phase diagram of the superconducting state. The superconducting (SC) phase induction mechanism is determined taking into account polarization contributions in the second-order perturbation theory in the Coulomb interaction. The results obtained for the angular dependence of the superconducting gap in different channels are compared with angule-resolved photoemission spectroscopy (ARPES) results. The influence of long-range hops in the phase diagram and critical superconducting transition temperature in different channels is analyzed. The conditions for the appearance of the Kohn-Luttinger superconductivity with the $d_{x^2 - y^2 } $ symmetry and high critical temperatures T c ~ 100 K near the half-filling are determined. 相似文献
19.
Using the formfactors which are entire analytic functions in a momentum space, nonlocality is introduced for a wide class of interaction Lagrangians in the quantum theory of one-component scalar field φ(x). We point out a regularization procedure which possesses the following features:
- The regularizedS δ matrix is defined and there exists the limit $$\mathop {\lim }\limits_{\delta \to 0} S^\delta = S.$$
- The Green positive-frequency functions which determine the operation of multiplication in \(S \cdot S^ + \mathop = \limits_{Df} S \circledast S^ + \) can be also regularized ?δ and there exists the limit $$\mathop {\lim }\limits_{\delta \to 0} \circledast ^\delta = \circledast \equiv .$$
- The operator \(J(\delta _1 ,\delta _2 ,\delta _3 ) = S^{\delta _1 } \circledast ^{\delta _2 } S^{\delta _3 + } \) is continuous at the point δ1=δ2=δ3=0.
- $$S^\delta \circledast ^\delta S^{\delta + } \equiv 1at\delta > 0.$$ Consequently, theS-matrix is unitary, i.e. $$S \circledast S^ + = S \cdot S^ + = 1.$$
20.
J. Halbritter 《Applied Physics A: Materials Science & Processing》1986,39(1):49-57
Broad-area electrodes show electron emission already at electric field strengthsF≈107 V/m. This enhanced field emission (EFE) occurs only for contaminated surfaces. EFE is accompanied by photon emission and gas desorption yielding finally discharges. EFE is caused by dust and contaminants initiating the following effects: an electron is stochastically emitted in a trigger zone the electron gains energyΔE?eΔxF * which excites electronic states which relax by the emission of electrons, photons, and atoms where the positive charges left behind enhanceF *=βF (β?1) initiating so an electron avalanche, i.e., a high conductivity channel. Because of charge migration and neutralization, this avalanche has a life time. This pulsating EFE is accompanied by light emission and gas desorption yielding finally a gas cloud and a discharge. The pulsating, self-sustained EFE has the same root as: the enhanced secondary emission found first by Malter the conductivity switching exhibited by thin (≈ 1 μm) layers of semiconductors or insulators the normal cathode fall and the firing-wave instability in neurodynamics. 相似文献