Third order wave equation in Duffin-Kemmer-Petiau theory. Massive case

Within the framework of the Duffin-Kemmer-Petiau (DKP) formalism a more consistent approach to the derivation of the third order wave equation obtained earlier by M. Nowakowski [Phys.Lett.A {\bf 244} (1998) 329] on the basis of heuristic considerations is suggested. For this purpose an additional algebraic object, the so-called $q$ - commutator ($q$ is a primitive cubic root of unity) and a new set of matrices $\eta_{\mu}$ instead of the original matrices $\beta_{\mu}$ of the DKP algebra are introduced. It is shown that in terms of these $\eta_{\mu}$ matrices we have succeeded in reducing a procedure of the construction of cubic root of the third order wave operator to a few simple algebraic transformations and to a certain operation of the passage to the limit $z \rightarrow q$, where $z$ is some complex deformation parameter entering into the definition of the $\eta$ - matrices. A corresponding generalization of the result obtained to the case of the interaction with an external electromagnetic field introduced through the minimal coupling scheme is carried out and a comparison with M. Nowakowski's result is performed. A detailed analysis of the general structure for a solution of the first order differential equation for the wave function $\psi(x; z)$ is performed and it is shown that the solution is singular in the $z \rightarrow q$ limit. The application to the problem of construction within the DKP approach of the path integral representation in parasuperspace for the propagator of a massive vector particle in a background gauge field is discussed.Comment: 39 page

The effect of alternating current on the current states of a quantum interferometer shunted by a superconducting inductance

The patterns of reversible changes in the critical current and discrete current states of a structure in the form of a superconducting quantum interferometer shunted by superconducting inductance, as a result of passing an alternating transport current through the structure and applying an external alternating magnetic field simultaneously with a direct transport current, was established. A new type of discrete stationary state was discovered during the transition of the interferometer to the resistive state caused by the combined action of direct and alternating transport currents.Comment: 6 pages, 9 figure

Locally frozen magnetic field in HTSC ceramics

The value of a locally frozen magnetic field in a region with a diameter of 0.5 mm in a 0.5-mm-thick YBa2Cu3O7-x plate was investigated as a function of the excitation field (to 2x10^4 A/m), plate cooling mode (in the absence or presence of a field; i.e., zero-field cooling (ZFC) or field coupling (FC)), and local demagnetizing field. Analysis of the measurement results in the noted range of excitation fields showed the following: (i) the dependence on the excitation field for the ZFC mode is explained by the local inhomogeneity of critical currents of weak links in the ceramic Josephson medium and is limited by their maximum value at the temperature of the experiment (77 K); (ii) the dependence on the excitation field for the FC mode contains a portion of the magnetic phase transition from the frozen current structure, typical of the initial portion of the dependence, to the current structure characteristic of the ZFC freezing mode, and is limited by this transition; and (iii) the dependence on the demagnetizing field for the ZFC mode can be explained by the stable coexistence (without annihilation) of microscopic current loops with opposite current directions in the ceramics.Comment: 6 pages, 5 figure

Parameters of the 125Te compound state cascade gamma-decay

Reliable information on level density and radiative strength functions for the excitation energy region with density of excited states more than 100 levels per 1 MeV and higher can be obtained now only by its model-free extraction from intensities of two-step cascades proceeding between compound states and few low-lying levels. Full model-free determination of these parameters in any method is possible only if one can extract from additional experimental information about general trend in dependence of ratio of strength functions of emitted reaction products of a given type on excitation energy of the nucleus under study. Analysis of the available experimental data for 125Te shows that the peculiarities observed earlier in other nuclei are also inherent to this nucleus.Comment: 24 pages, 5 figures, 1 tabl

Order-disorder transition induced by deformation of vortex lines at the twin boundaries in YBa2_2Cu3_3O7−δ_{7-\delta}-crystals: test of the Lindemann criteria

We show that rotation of the magnetic field off the plane of twin boundaries (TB's) induces transition of an ordered vortex solid phase to a disordered one. This transition arises due to appearance of transverse deformations of vortex lines near the TB's, $u_{t,TB}$, the amplitude of which satisfies the Lindemann criteria, $u_{t,rp}=c_La_0$. This order-disorder transition is accompanied by an increase in the depinning current, by crossover from an elastic creep to plastic one, and by appearance of the $S$-shaped voltage-current characteristics.Comment: 4 pages, 4 figure

Quantization of diamagnetic current in a superconducting ring with the Josephson point contact

It was established experimentally that a critical value of the diamagnetic current, excited by an external magnetic field in a superconducting ring (with an inductance of about ~ 10^-6 H) with a Nb-Nb clamping point contact having the Josephson contact properties is a strictly periodic function of field strength, despite the complex microstructure of the clamping contact. The reasons of the periodic dependence are discussed on a basis of the interference model of diamagnetic current and quantized values of the circulating current in the microinterferometer formed by the clamping contact.Comment: 4 pages, 3 figure

Measurement of energy gaps in superconductors by means of quantum interference devices

The effect of temperature on the form of discrete changes in the current in highly inductive (~10-6 H) doubly-connected superconductors with niobium-niobium clamped point contacts is determined experimentally. The magnitude and duration of the voltage pulse on a doubly-connected superconductor is measured at the time of the discrete change in its current state. The pulse magnitude is close to the energy gap 2D/e of the superconductor and its duration (~10-6 s) corresponds to the minimum possible time (~10-12 s) for a change in the state of the contact when the depairing current through it is reached. The measurement data are discussed in terms of models of the quantum interference of currents in a doubly-connected superconductor with clamped point contacts in the form of a quantum interferometer.Comment: 7 pages, 5 figure

Detection of self-oscillations of the transport current in a doubly connected superconductor

It has been found experimentally that when dc current is passed through a circuit consisting of two superconductors connected in parallel and reaches its critical value in one of the circuit branches the current in the branches undergoes quasi-harmonic undamped oscillations. The mechanism resulting in the appearance of the self-oscillations is discussed. The characteristics of magnetic field freezing in a circuit with self-oscillating current are examined.Comment: 3 pages, 3 figure

Bethe-Salpeter approach with the separable interaction for the deuteron

Recent developments of the covariant Bethe-Salpeter (BS) approach with the use of the separable interaction for the deuteron are reviewed. It is shown that the BS formalism allows a covariant description of various electromagnetic reactions like the lepton-deuteron scattering, deuteron electro-disintegration, deep inelastic scattering (DIS) of leptons on light nuclei. The procedure of the construction of the separable nucleon-nucleon (NN) interaction is discussed. The BS formalism facilitates analysis of the role of the P-waves (negative energy components) in the electromagnetic properties of the deuteron and its comparison with the nonrelativistic results. Furthermore the covariant BS approach makes it possible to analyze DIS of leptons from the deuteron in a model independent way and to extend the formalism to DIS reactions on the light nuclei.Comment: 87 pages, 20 figures, to be published in Prog.Part.Nucl.Phys. v.48, no.

Freezing and quantization of current passing through a doubly connected superconductor with a point contact

The particulars of dc current passage through a structure consisting of a doubly connected superconductor (DCS) with branches that are asymmetric with respect to length and critical current have been investigated experimentally. The short branch, which has the lowest critical current, was a clamping niobium-niobium point contact with length comparable to the coherence length of the superconductor. In contrast to a previously studied DCS with a short branch much longer than the coherence length, it was found that when the short-branch current reaches the critical value the currents in the branches of the DCS do not undergo self-excited oscillations; a current exceeding the critical value enters the long branch when this current is increased in portions (is quantized), and when it is subsequently decreased it freezes partially or completely in the DCS circuit.Comment: 6 pages, 4 figure