Calculation of intrinsic magnetic fields in thin films

The calculation of intrinsic fields on the basis of a simple film model is proposed. It reveals the dependence of stray field interaction on the film structure.     

Resistive transitions of superconducting thin films in strong electric fields

We report discontinuous current-induced transitions to the normal state of superconducting thin films in the mixed state. The results obtained are in qualitative agreement with the recent theory of Thompson and Hu of dynamic instabilities of vortices.     

Non-equilibrium superconductivity in homogeneous thin films

A review is given of non-equilibrium phenomena in thin homogeneous superconducting films. The basic theoretical concepts necessary for understanding the experiments are discussed. Experiments on non-equilibrium states created by microwave, laser or phonon irradiation, quasiparticle injection through tunnel barriers, time-dependent externally supplied currents and thermal gradients are described. The emphasis of the paper is on the resulting physical phenomena such as the enhancement of superconductivity, charge imbalance, order parameter relaxation and changes in the superconducting energy gap.     

High field superconductivity in thin films

Thin films provide an ideal means for studying the role of spin paramagnetism in the theory of superconductivity. A review is given of the theoretical and experimental work available until now with respect to this problem. It includes a study of the excitation spectrum of thin films in a parallel magnetic field and the experimental evidence of Zeeman splitting of superconducting quasiparticles. The role of spin-orbit interaction is discussed in detail. The application of spin selective tunnelling is shown. Furthermore, it includes a study of the order of phase transition between the normal state and the paramagnetically limited superconducting state. A detailed discussion is given of the generalized Ginzburg-Landau equation including numerical evaluations. The applicability of Tinkham's formula is discussed, which is relevant for the determination of critical fields of arbitrary orientations to the film. Finally, account is given of the work which deals with the influence of spin paramagnetism on superconducting fluctuations. Recent experimental and theoretical work is described and discussed.     

Disorder and quantum fluctuations in superconducting films in strong magnetic fields

We find that the upper critical field in a two-dimensional disordered superconductor can increase essentially at low temperatures. This happens due to the formation of local superconducting islands weakly coupled via the Josephson effect. The distribution of the superconducting islands is derived. It is shown that the value of the critical field is determined by the interplay of the proximity effect and quantum phase fluctuations. The shift of the upper critical field is connected with the pinning properties of a superconductor.     

Domain-wall dynamics in ferrite garnet films in strong in-plane magnetic fields

The domain-wall dynamics in the ferrite garnet films with the (111) orientation has been investigated by twofold high-speed digital photography in the presence of a magnetic field close in strength to the anisotropy field.     

Certain aspects of domain-wall dynamics in thin magnetic films in pulsed fields

An analysis is made of experimental information on the domain-wall mobility in permalloy films in pulsed external fields. Both single pulses and pulse trains, with various temporal parameters, are considered. The experimental results are compared with a solution of the equation of motion for the domain walls.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 2, pp. 64–67, February, 1971.     

Third-order phase transition and superconductivity in thin films

We have found a new mean field solution in the BCS theory of superconductivity. This unconventional solution indicates the existence of superconducting phase transitions of third order in thin films, or in bulk matter with a layered structure. The critical temperature increases with decreasing thickness of the layer, and does not exhibit the isotope effect. The electronic specific heat is a continuous function of temperature with a discontinuity in its derivative.     

Grantmakher-Kaner effect in strong magnetic fields

Gantmakher-Kaner (GK) effect in a compensated metal is studied theoretically. The dependence of the amplitude of GK oscillations from the polarization of exciting radio-frequency field is found. Effect results from the excitation of doppleron in the plate. In polarization, in which the doppleron exists, the part of skin-layer field energy, contained in harmonics with the length close to cyclotron displacement of resonant carriers, is carried into the slab by doppleron. This results in decreasing of GK oscillations in this polarization in comparison with an opposite one.     

Exciton condensation in strong magnetic fields

The density correction to the chemical potential of excitons in a strong magnetic field was calculated. The possibilities of Bose-Einstein condensation of excitons and their condensation into electron-hole liquid (EHL) were studied. Magnetic field ranges in which these processes can be observed were determined.     

Coulomb collisions in strong magnetic fields

Summary Scattering cross-sections, reflection and transmission coefficients are derived for charged-particle potential scattering in the presence of a quantizing constant magnetic field within the Green's function approach. The optical theorem and the limit of the cross-section for vanishing values of the magnetic field have also been obtained. A numerical analysis of the total cross-section for different magnetic-field intensities and values of the screening constant has been performed. The total cross-sections are found to differ significantly from the field-free ones only for magnetic-field intensities and incident particle energies such that only few Landau channels are open. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Radiative process in strong magnetic fields

Abstract

The behavior of electromagnetic processes in strong magnetic fields is currently of great interest in high-energy astrophysics. Observations of neutron stars indicate that magnetic fields larger than 10¹² Gauss exist in nature. In fields this strong, where electrons behave much as if they were in bound atomic states, familiar processes undergo profound changes and exotic processes become important. Strong magnetic fields affect the physics in several fundamental ways: energies prependicular to the field are quantized, transverse momentum is not conserved and electron/positron spin is important. The relaxation of transverse mometum conservation allows first order processes and their inverses: one-photon pair production and annihilation, synchrotron/cyclotron radiation and absorption, which are kinematically forbidden under field-free conditions. The first two are essentially quantum-mechanical and hence significant only in fields whose strength approaches the critical field, B _cr = 4.414 × 10¹³ Gauss. One-photon pair production is likely to be the dominant source of e ⁺ -e ^? pairs in fields exceeding 10¹² Gauss. While synchrotron radiation and absorption are observable as classical electromagnetic processes in weak fields, they are considerably different in high fields, where the classical synchrotron radiation formulae can violate conservation of energy, and predict too large an emissivity and electron energy loss rate. The second-order processes: two-photon pair production and annihilation and Compton Scattering, are also modified in strong fields. The discreteness of e ⁺ - e^? pair states causes resonant behavior in the cross sections and decreases the second-order rates from their free-space values. These processes play an important role in modelling high energy emission from pulsars and gamma-ray bursts.     

Andreev reflection in strong magnetic fields

We have studied the interplay of Andreev reflection and cyclotron motion of quasiparticles at a superconductor-normal-metal interface with a strong magnetic field applied parallel to the interface. Bound states are formed due to the confinement introduced by both the external magnetic field and the superconducting gap. These bound states are a coherent superposition of electron and hole edge excitations similar to those realized in finite quantum-Hall samples. We find the energy spectrum for these Andreev edge states and calculate transport properties.     

Anisotropy of atoms in strong magnetic fields

The anisotropy of the atomic electronic density caused by strong magnetic fields is discussed here in the context of the statistical theory. In the framework of the current-density functional theory, a derivation is given of the gradient terms, necessary for anisotropy, based on the polarizability of free electrons in a magnetic field. Numerical results for the electronic density show a strong elongation of the electronic density along the field direction. In very high magnetic fields the electronic density is localized in thin columns along the field.     

Screening of impurities in strong magnetic fields

Charged impurities inserted in an electron gas in strong magnetic fields and at low temperatures are considered. Using the random phase and the generalized Born approximations, a self-consistent calculation of the screening of the impurities and the broadening of the electronic energy levels due to the scattering by these impurities is presented. Concrete results obtained in numerical form show that for typical semiconductors the anisotropy of te screening induced by the magnetic field is strongly reduced by collisional damping. The screening length, however, depends rather strongly on the field.On leave of absence from the Department of Physics, University of Tokyo, Tokyo, Japan.     

Effect of chemisorption on superconductivity of thin metal films

The mechanism of effective attraction of electrons in a thin metal film due to interaction with oscillations of adsorbed atoms is considered. At a sufficiently narrow resonance electron level close to the Fermi level this interaction has a resonance character and, therefore, makes a great contribution to the effective attraction constant. The temperature of the superconducting transition T_c with due regard to this mechanism has been calculated and shown to lead to a considerable increase of T_c.