Spin structure of the quark-quark confining interaction and the mass spectra of bound quark-antiquark systems in the framework of the Salpeter equation

The mass spectrum of bound quark-antiquark systems is calculated in the framework of the Salpeter equation with the spin structurex ₁ ⁰ ₂ ⁰ of the confinement part of the quark-quark interaction potential. It is shownthat for the case of heavy quarks the results practically do not depend on the value of the mixing parameterx. As to the case of light quarks, the solutions of the Salpeter equation exist only if 0.5x1, but the mass spectrum does not depend very much on the values ofx out of this interval.     

Phase diagrams and magnetic properties of diluted Ising and Heisenberg magnets with competing interactions

Ising and Heisenberg magnets with nearest-neighbor ferromagnetic exchangeJ ₁ and next-nearest antiferromagnetic exchangeJ ₂ and randomly distributed frozen-in nonmagnetic impurities of arbitrary concentration 1–x are studied by several methods: systematic series expansions inx, 1–x and inverse temperature (1/T) as well as Monte Carlo simulation. Depending onRJ ₂/J ₁,T andx the model is in paramagnetic, ferromagnetic, antiferromagnetic or spin glass phases. The microscopic magnetic structures of all these phases are investigated and found to be more complicated than usually (e.g., the ferromagnetic state contains spins and clusters either aligned antiparallel or not aligned at all, when frustration effects make bonds ineffective). We suggest that the concentrationx _c of magnetic ions below which no (anti-)ferromagnetic long range order occurs depends onR continuously, andx _c 1 at the multicritical point (R _m ,T=0) where the order changes from ferromagnetic to antiferromagnetic. Our results for phase diagram, susceptibility etc. are compared to recent data on the Eu _x Sr_1–x S system and very good agreement is found.     

Electronic structure of amorphous Nb1-x Si x films studied by X-ray emission and X-ray photoelectron spectroscopy

We present valence band spectra of the amorphous system Nb_1–x Si _x (0.2x0.8), of bcc-Nb and of a-Si obtained by X-ray photoelectron spectroscopy (XPS, Al K) and X-ray emission spectroscopy (XES, Si K-emission bands). The samples were prepared as thin films by sputtering. The origin of all prominent spectral features was identified and consistently correlated to Si 3s-, Si 3p-and Nb 4d-derived states. The Nb4d-Si3p coupling is stable in binding energy over a wide concentration range. There is strong experimental evidence that the short range order changes considerably within the concentration interval 0.4x0.7, whereas the partial density of states of the Si 3p-electrons is clearly altered in the small concentration range 0.50x0.57.     

Unexpected magnetic behaviour in a singlet crystal field ground state induced by Tb 4f-instability

The magnetic susceptibility () of Th_1-x Tb _x alloys (with 5<x<55a/o Tb) in the range of 1 K<T<350K and the specific heat (forx=1.5a/o Tb) for 0.5<T<10 K were measured. A maximum in (T) was observed at a temperature which depends on concentration. The crystal field level scheme that fits the specific heat measurements shows two non-magnetic singlets as lowest levels. Such ambiguity is discussed within the framework of the 4f-Tb instability. The results are in agreement with the matrix superconductiveT _c decrease. The contribution of the interconfigurational mixing on and the specific heat is also discussed.This work was partially supported by the KfA-CNEA cooperation program and by the Deutsche Farschungsgemeinschaft through SFB125     

Characterization of laser-nitrided iron and sputtered iron nitride films

Laser-nitriding may be a promising technique for substituting conventional nitriding processes. We have irradiated pure iron with pulses of an excimer laser and achieved high nitrogen contents in a thin surface layer. We found that the nitrogen is dissolved into -Fe, leading to a large amount of retained austenite. This was also verified by X-ray diffraction (XRD) measurements. Three subspectra can be resolved in the Mössbauer spectra (CEMS) for this nitrogen austenite. The nitrogen concentration can be calculated in terms of site occupation, indicating a content as high as 16(1) at%, which is consistent with the results of Rutherford backscattering spectroscopy (RBS), resonant nuclear reaction analysis (RNRA) and Auger electron spectroscopy (AES) measurements. This is more than the solubility limit for -Fe(N). By reactive magnetron-sputtering it is possible to produce thin iron nitride films of various stoichiometries. We report on the production of-Fe _x N and FeN _y films. These films were again characterized by CEMS, RBS, RNRA (¹⁵N(p, )) and XRD. For-Fe _x N, produced in the range 2x3 with medium nitrogen flows during reactive sputtering, the Mössbauer spectra can be well resolved in terms of different iron sites, enabling an accurate calculation of the nitrogen content. For high nitrogen flows during sputtering a phase FeN _y withy>0.5 is produced. This phase is not reported in the Fe-N phase diagram.     

NMR in Laves phase alloy system GdPt x —analysis of nonstoichiometry in intermetallic compounds

NMR is applied to ferromagnetic Laves phase compounds Gd_1–x A _x Pt₂ (A=Sc, La) and GdPt _x (2x3). The different hyperfine field contributions are analyzed. Neighbour contributions to the Gd hyperfine field and strength of ferromagnetic coupling are compared. It is found that there is a strong predominance of the nearest neighbour contribution (92%) to the Pt hyperfine field. We show that the Pt NMR allows to derive the deviation in occupation number of Gd atoms on Gd sites in nonstoichiometric compounds with about 4% accuracy.Now with Dürrwächter K. G., Pforzheim     

Symmetry conservation and integrals over local charge densities in quantum field theory

For conserved local currents ^µ j ^µ (x)=0 in quantum field theory it is shown that anR-dependence of _R (x ₀) inj ₀(f _R(x)· _R (x ₀)) leads to nicer properties than a fixed (x ₀). The behaviour of j ₀(f _R(x)·_R(x ₀) is discussed under this aspect.     

Contribution of quantum corrections and superconducting fluctuations to the magnetic field and temperature dependence of the conductivity in amorphous CuTi and CuZr alloys

We report conductivity measurements on Cu _x Ti_100–x and Cu _x Zr_100–x glasses as a function of magnetic field (0B6T) and temperature (1.5–5. At low temperatures the measured conductivity(T,B)= ₀+(T)+(B,T) is compared quantitatively with the predictions of diagrammatic perturbation theories including quantum interference effects, spin-orbit scattering and electron-electron interaction. We obtain a set of characteristic fields for inelastic and spin orbit scattering from both the magnetic field and the temperature dependence of the measured (T, B). Below about 4K the Coulomb interaction determines (T) in consistence with the Hall effect, whereas quantum interference processes and spin-orbit scattering dominate the magnetic field dependence. In case of Cu _x Zr_100–x , (B, T) can be explained by taking into account superconducting fluctuations (Maki-Thompson and Aslamasov-Larkin parts) in addition. Superconducting fluctuations dominate the temperature dependence as well. For high magnetic fields and lower temperatures (B/T>1T/K) we find discrepancies between experiment and calculations from perturbation theory.     

On the theory of layered high-temperature superconductors

Assuming that charge carriers form a Fermi liquid state, we study a model for layered high-temperature superconductors with unretarded intralayer and interlayer pairing. Guided by band structure calculations and inverse photoemission experiments, we adopt a tight binding band with nearest and next-nearest neighbors hopping within the sheets and weak interlayer hopping. The gap equations are solved numerically, without imposing a cutoff energy, characteristic to phonon mediated superconductivity. On this basis we calculate the gap parameters,T _c , the tunneling conductance, infrared absorption and the coherence length for various band fillings =1/2–x by introducing excess holes of concentrationx. Assuming the interlayer coupling strength to be smaller than the intralayer one, our main results are as follows:T _c is dominated by the intralayer properties, reaching a maximum atx0.3, where strong coupling features appear. In the presence of interlayer pairing, the gap becomes anisotropic perpendicular to the layers, and standard BCS-behavior is modified. In particular the BCS-square root singularity in the density of states and in the tunneling conductance is replaced by van Hove singularities characterizing the anisotropic gap. In particular, we investigate the anisotropy of the tunneling conductance for specular and diffuse tunneling for a junction parallel or perpendicular to the layers, infrared absorption, as well as the coherence length, parallel and perpendicular to the layers.     

Structural and magnetic properties of rapidly solidified (Ce0.2Fe0.8)1-x Al x ribbons determined by X-ray diffraction and Mössbauer spectrometry

(Ce_0.2Fe_0.8)_1-x Al _x (0 x 0.9) ribbons have been prepared by planar flow casting under an He atmosphere with a linear velocity of 29 m s^-1. Analyses of the ribbons by X-ray diffraction and⁵⁷Fe Mössbauer spectrometry in the temperature range 4–300 K show that all the ribbons are crystalline. With increasingx, the observed phases are Ce(Fe, Al)₂, Ce₂(Fe, Al)₁₇, CeFe_4+y,Al_8-y and the single fcc aluminium phase. For the different phases, the line intensities of the Mössbauer spectra agree with previous results on the preferential substitution sites for aluminium. A coherent hyperfine parameters set was deduced from fitting spectra in the temperature range 4–300 K.     

Diamagnetism and muon Knight shift in semiconducting Bi1−x Sb x single crystals

The Knight shift of positive muons (⁺) implanted in semiconducting single crystals of Bi_1–x Sb _x (x=0.085, 0.14, 0.19) has been measured as a function of temperature and sample orientation. The Knight shift (KS) is generally negative and is found to scale with the negative total macroscopic susceptibility; the scaling is independent ofx but dependent on the orientation. One concludes that only the valence and conduction bands near theL-symmetry point in the Brillouin zone contribute to the ⁺ Knight shift, most likely by the contact hyperfine interaction. Furthermore the valence bands and the conduction bands seem to be associated with the same hyperfine coupling constants. These conclusions are quite unexpected and call for a new theoretical approach.     

On the three-body long-range scattering problems

In this Letter, we give results on precise microlocalized time-decay estimates in three-body long-range scattering problems. We prove the asymptotic completeness of wave operators in three-body long-range scattering for a class of long-range interactions of the form V ₁(x)+V ₂(x), where V ₁ is nonnegative and decays like O(|x|^–0), for some ₀ > 1/2 and V ₂ decays like O(|x|^-y) for some > 2(1–₀)/₀.     

Structural and optical properties of ZnSe x Te1−-x solid solutions in thin-film form

Solid solutions of ZnSe _x Te_1–x (0. 1 x 1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc-blende structure. The calculated unit cell lattice constant (a) for the different compositions in powder form vary linearly, with molecular fractionx following Vegard's law:a(x) = 6.165 – 0.485x. Thin films of ZnSe _x Te_1–x (0.1 x 1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10^–4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe _x Te_1–x polycrystalline films of different compositions have two direct transitions with corresponding energy gapsE _g andE _g + _so The variations in bothE _g andE _g + _so, withx indicate that ZnSe _x Te_1–x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.     

Matter and light wave interferometry in gravitational fields

We consider the problem of finding the quantum mechanical phase associated with the propagation of a particle in a given external gravitational field, and conclude that it ism ds. In weak fieldsh this allows us to calculate the gravitationally induced phase on a freely traveling particle as 1/2 h P dx whereP is the ordinary momentum. This formula has the expected Newtonian limit and is then used to calculate effects in matter wave interferometry such as those due to gravity waves and the dragging of the ether frame by rotating bodies. Light wave interferometry is then considered and is shown to be also described by 1/2 h K dx , whereK is the wave vector of the light, and the integral is along the path of the ray. Matter and light wave interferometry are compared in various cases.A preliminary version of this work was presented at the Grenoble Workshop on Neutron Interferometry, June 1978.     

Heavy-fermion behavior and spin-glass freezing in Si-stabilized amorphous alloys based on UPt3

U-Pt-Si and U-(Pt, Pd)-Si alloys have been prepared in the amorphous state by splat-cooling. The average nearest-neighbor distance is the same as the U-Pt distance in UPt₃. The low-temperature behavior of these alloys (with composition (U_0.25Pt_0.75)_1–xSi_x, x=0.18, 0.20, 0.25; and (U_0.25(Pt_1–yPd_y)_{0.75 0.8}Si_0.2,y=0.05 and 0.1) has been studied by specific heatC, magnetization and resistivity measurements in the temperature range 1.5 K to 20 K and for magnetic fields up to 6 T. Some samples were investigated down to 0.1 K and the specific heat for one sample was measured in fields up to 22 T. With ₀ =C/T| _T0 between 0.25 and 0.35 J/moleUK², the alloys can be classified as heavy-fermion materials. As opposed to UPt₃, the alloys exhibit spin-glass behavior with a concomitant decrease of ₀. The magnetization exhibits typical spin-glass features (e.g., an irreversibility line). An inverse relationship between ₀ andT _max (temperature ofC/T maximum which is proportional to the spin-glass freezing temperature), irrespective of the Pd content, is observed. The behavior can be qualitatively described by a coexistence of heavy-fermion behavior and spin-glass freezing.     

Mössbauer investigation of In and Sc substituted barium hexaferrite

A detail Mössbauer analysis has been performed on polycrystalline samples of hexagonal ferrites with composition BaFe_12-x In _x O₁₉ (0x4) and BaFe_12-x ScxO₁₉ (0x3). The dependence on composition of the distribution of metallic cations among the five sublattices of the structure has been determined: these data confirm the strong preference of Sc and In ions for the sites belonging to the R block.As a consequence iron ions located in the main spin up sublattice (12k) with different number of neighbouring Fe³⁺ ions display different temperature dependences of the magnetization. The occurrence of non-collinear spin configurations, even for very low degrees of substitution of iron, has also been evidenced.     

Inertial effects on the escape rate of a particle driven by colored noise: An instanton approach

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.     

Logically independent von Neumann lattices

Three definitions of logical independence of two von Neumann latticesP₁,P₂ of two sub-von Neumann algebras ₁, ₂ of a von Neumann algebra are given and the relations of the definitions clarified. It is shown that under weak assumptions the following notion, called logical independence is the strongest:A B 0 for any 0 A P₁, 0 B P₂. Propositions relating logical independence ofP₁,P₂ toC ^*-independence,W ^* independence, and strict locality of ₁, ₂ are presented.     

Ballistic annihilation and deterministic surface growth

A model of deterministic surface growth studied by Krug and Spohn, a model of the annihilating reactionA+Binert studied by Elskens and Frisch, a one-dimensional three-color cyclic cellular automaton studied by Fisch, and a particular automaton that has the number 184 in the classification of Wolfram can be studied via a cellular automaton with stochastic initial data called ballistic annihilation. This automaton is defined by the following rules: At timet=0, one particle is put at each integer point of . To each particle, a velocity is assigned in such a way that it may be either +1 or –1 with probabilities 1/2, independent of the velocities of the other particles. As time goes on, each particle moves along at the velocity assigned to it and annihilates when it collides with another particle. In the present paper we compute the distribution of this automaton for each timet . We then use this result to obtain the hydrodynamic limit for the surface profile from the model of deterministic surface growth mentioned above. We also show the relation of this limit process to the process which we call moving local minimum of Brownian motion. The latter is the processB _x ^min ,x , defined byB _x ^min min{B _y ;x–1yx+1} for everyx , whereB _x ,x , is the standard Brownian motion withB ₀=0.     

Ion irradiation—a technique providing a criterion to distinguish between amorphous and nanocrystalline In1−x Pd x films

In_1–x Pd _x films with 0.2x0.75 have been prepared by vapour quenching at 4.2 K or 77 K, respectively. To test whether amorphous (a-) phases can be obtained in this way, the resistance behavior and the electron diffraction patterns of the as-prepared and annealed films were studied insitu. For films withx=0.25 additional information could be acquired from their superconducting behavior. Combining these results one concludes that a-phases exist for the compositional range 0.2x0.6, which are stable up to crystallization temperaturesT _x within the range 250 KT _x 420 K. Irradiation of the crystallized films at low temperatures (4.2 K or 77 K) with heavy ions (350 keV Ar⁺ or Kr⁺) leads to complete re-amorphization. Forx=0.67 corresponding to InPd₂ a nanocrystalline (n-) phase is obtained by vapour quenching at 77 K as inferred from x-ray diffraction. AtT _x =700 K, thesen-films exhibit a drop of the electrical resistance indicating the beginning of significant grain growth. After recooling, Kr⁺ bombardment at 77 K does not restore the high electrical resistance of the as-quenchedn-film. This result can be used as a criterion when studying quenched films withx=0.625 corresponding to In₃Pd₅. In this case, a resistance drop is found atT _x =600 K, but the diffraction techniques do not allow an uniquevocal distinction between amorphous and nanocrystalline. This becomes possible by low temperature ion irradiation after annealing atT>T _x . The bombardment results in resistance changes, which saturate well-below the value of the as-quenched sample implying nanocrystallinity for the latter. Based on this criterion, a phase-diagram for quenched In_1–x Pd _x is provided with 0x1 containing the newly detecteda- andn-phases.