Nonlinear electrodynamics near a superconducting string

We calculate the effective action for photons in an arbitrary external field using the expansion in the inverse of the mass of the electron. The resulting effective lagrangian is used to calculate magnetization of the vacuum in the vicinity of a superconducting string. The magnetization current partially screens the current in the string and slows down the rate of growth of the current there. We also discuss the scattering of electromagnetic waves on a superconducting string with the nonlinear effects taken into account.     

Dendritic flux avalanches and nonlocal electrodynamics in thin superconducting films

We report a mechanism of nonisothermal dendritic flux penetration in superconducting films. Our numerical and analytical analysis of coupled nonlinear Maxwell and thermal diffusion equations shows that dendritic flux pattern formation results from spontaneous branching of propagating flux filaments due to nonlocal magnetic flux diffusion and positive feedback between flux motion and Joule heating. The branching is triggered by a thermomagnetic edge instability, which causes stratification of the critical state. The resulting distribution of thermomagnetic microavalanches is not universal, because it depends on a spatial distribution of defects. Our results are in good agreement with experiments on Nb films.     

Low-energy electrodynamics of superconducting diamond

Heavily boron-doped, diamond films can become superconducting with critical temperatures Tc well above 4 K. Here we first measure the reflectivity of such a film down to 5 cm(-1), by also using coherent synchrotron radiation. We thus determine the optical gap 2Delta, the field penetration depth lambda, the range of action of the Ferrell-Glover-Tinkham sum rule, and the electron-phonon spectral function alpha2F(omega). We conclude that diamond behaves as a dirty BCS superconductor.     

Nonlinear acoustoelectronic interaction in thin superconducting lead films

The effect of high-power surface acoustic waves (SAW) on the superconducting state of Pb films has been studied in different transverse magnetic fields. It was established that a high-intensity sound wave affects the T _c of the film and the character of the superconducting transition, and that the observed changes are the larger, the higher is the SAW intensity. It was found that high-power SAW are capable of inducing vortex depinning in the film and reducing the critical current. Various mechanisms which are responsible for the nature of these effects are discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1753–1760 (October 1997)     

Modulation instability of electromagnetic excitations in the nonlocal Josephson electrodynamics of thin magnetic superconducting films

The modulation instability of plane finite-amplitude nonlinear waves with the Josephson frequency is studied for a Josephson contact in thin nonmagnetic and magnetic (two-dimensional) superconducting films. Dispersion relations for the increments of small-amplitude perturbations are derived. Modulation instability is shown to develop in the finite range 0<Q<Q _b of the wavevectors of amplitude perturbations for the nonmagnetic films and for any perturbation wavevector 0<Q<∞ for the magnetic films.     

Nonlinear approach to electrodynamics

A nonlinear approach to electrodynamics is reviewed. On imposing a nonlinear constraintA A = – ², together with the usual gauge-invariant electromagnetic field Lagrangian, it is found that the resulting equations of motion have, besides the photon, a static spherically symmetric extended solution which may be regarded as a charged particle. A magnetic dipole moment (spin) can also arise as a solution of the equations of motion if, as expected, it is treated as a first-order quantum effect. In the limit for small quantum fields and pointlike charged particles, the quantum mechanical equivalence of the approach with the usual Lagrangian formulation of the electromagnetic interaction of a charged scalar field is heuristically shown. Moreover the possibility of constructing charged fermion fields from the solution having both a charge and a magnetic moment is illustrated. In such an approach the photon is associated with the spontaneous breaking of Lorentz symmetry, and the emission of soft photons does not exhibit any infrared divergences.     

Nonlinear arcsin‐electrodynamics

A new model of nonlinear electrodynamics with three parameters is suggested and investigated. It is shown that if the external constant magnetic field is present the phenomenon of vacuum birefringence takes place. The indices of refraction for two polarizations of electromagnetic waves, parallel and perpendicular to the magnetic induction field are calculated. The electric field of a point‐like charge is not singular at the origin and the static electric energy is finite. We have calculated the static electric energy of point‐like particles for different parameters of the model. The canonical and symmetrical Belinfante energy‐momentum tensors and dilatation current are obtained. We demonstrate that the dilatation symmetry and dual symmetry are broken in the model suggested.

     

Nonlinear electrodynamics and anisotropic space-time

The metrical properties of four-space in the presence of a nonlinear electromagnetic field in vacuum are investigated. It is shown that the metric induced by the nonlinear electromagnetic field has a complicated nature and corresponds to an anisotropic space-time, i.e., to a four-space in which birefringence is observed. A special case of such a space is ordinary Riemann-Euclid space. As an example, the influence on the metric of the radiative corrections that follow from quantum electrodynamics is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 52–55, April, 1980.     

Nonlinear electrodynamics in space-times with torsion

A nonminimal and nongauge invariant descirption of nonlinear electrodynamics in space-times with torsion is given. It is shown that in the case of the Weitzenböck teleparallel space-time, massive photons are produced by a mechanism which involves the nonminimal coupling constant and the divergence of the torsion vector.On leave of absence from: Grupo de Relatividade e Teoria de Campo, Instituto de Fisica — UERJ, Departamento de Fisica Teorica, 20550 Maracan, Rio de Janeiro, Brazil     

Nonlinear electrodynamics in a superstrong magnetic field

Using a Feynman technique in a two-dimensional space we have calculated an electron propagator and a photon polarization tensor in a superstrong magnetic field $\text{B ? B}{}_{\mathrm{<mtext>0</mtext>}}\text{=}\text{m}{}^{\mathrm{<mtext>2</mtext>}}\text{e}\text{=}\text{4.41 × 10}{}^{13}$ G. Some applications are briefly discussed.     

Far-infrared electrodynamics of superconducting Nb: comparison of theory and experiment

Complex conductivity spectra of superconducting Nb are calculated from the first principles in the frequency region around the energy gap and compared with the experimental results. The raw experimental data obtained on thin films can be precisely described by these calculations.     

Nonlinear electrodynamics coupled to teleparallel theory of gravity

Using nonlinear electrodynamics coupled to teleparallel theory of gravity, regular charged spherically symmetric solutions are obtained. The nonlinear theory is reduced to the Maxwell one in the weak limit and the solutions correspond to charged spacetimes. One of the obtained solutions contains an arbitrary function which we call general solution since we can generate from it the other solutions. The metric associated with these spacetimes is the same, i.e., regular charged static spherically symmetric black hole. In calculating the energy content of the general solution using the gravitational energy--momentum within the framework of the teleparallel geometry, we find that the resulting form depends on the arbitrary function. Using the regularized expression of the gravitational energy--momentum we obtain the value of energy.     

Paraconductivity of superconducting tin films

Experimental results on paraconductivity of superconducting thin tin films are compared with theoretical predictions of the Maki-Thompson theory which includes a small correction term proposed by Imamura et al. It is found that the corrected Maki-Thompson expression for paraconductivity of thin superconducting films improves the fit between theory and experimental data at relatively higher temperatures. It also gives a smaller value of δ, a fitting variable in the M-T theory which is known as the pair- breaking interaction parameter, than the value obtained in the unmodified M-T expression for the paraconductivity.     

Long-range nonlocal flow of vortices in narrow superconducting channels

We report a new nonlocal effect in vortex matter, where an electric current confined to a small region of a long and sufficiently narrow superconducting wire causes vortex flow at distances hundreds of intervortex separations away. The observed remote traffic of vortices is attributed to a very efficient transfer of a local strain through the one-dimensional vortex lattice (VL), even in the presence of disorder. We also observe mesoscopic fluctuations in the nonlocal vortex flow, which arise due to "traffic jams" when vortex arrangements do not match a local geometry of a superconducting channel.     

MMW detection by superconducting films-applications of high temperature superconducting films

Conclusions Superconductors exhibit two basic modes of radiation detection —a thermal or bolometer mode and a rectification mode which depends on a nonlinear voltage-current characteristic. The SIS detector has been shown to have a quantum limited current responsivity of e/hf. By analogy, weak link detectors may have a quantum limited voltage responsivity of about 2eR/hf. Granular films behave like arrays of weak links.Both thermal and rectification modes have been observed in HTOS films. They can be characterized by the dependence of film resistance on temperature and current. Analysis of the temperature dependence of film resistance indicates that bolometer responsivities are limited by the broader resistive transition observed in HTOS films. HTOS films show a strong nonlinear dependence of resistance on current at lower temperatures. In this region, we expect voltage responsivities greater than 1 KV/W. This is a very promising mode for detection and mixing of far infrared and millimeter waves.     

Superimposed normal and superconducting films

Tunneling characteristicsdI/dV have been taken on both sides of “dirty”In - Bi/Zn superimposed films, the temperatureT being such thatIn - Bi was superconducting and Zn normal. Most of the attention has been devoted to the regionT～T _c where the experimental curves can be compared with a reasonably accurate microscopic theory. We find reasonable agreement for the voltage scale and, more important, for theamplitude of the effects in the superconducting phase.