Variational method to study vortex matter in mesoscopic superconductors

A simple variational model is proposed to analyze the superconducting state in long cylindrical type-II superconductor placed in the external magnetic field. In the framework of this model, it is possible to solve the Ginzburg-Landau equations for the states with axially symmetric distributions of the order parameter. Phase transitions between different superconducting states are studied in the presence of external magnetic field and an equilibrium phase diagram of thin cylinder is obtained. The lower critical field of the cylindrical type-II superconductor with arbitrary values of radius and Ginzburg-Landau parameter is found. The field dependence of the magnetization of thin cylinder, which can carry several magnetic flux quanta, is calculated.Comment: 10 pages, 5 figures, submitted to Physica

Effect of diffusive boundaries on surface superconductivity in unconventional superconductors

Boundary conditions for a superconducting order parameter at a diffusive scattering boundary are derived from microscopic theory. The results indicate that for all but isotropic gap functions the diffusive boundary almost completely suppresses surface superconductivity in the Ginzburg-Landau regime. This indicates that in anisotropic superconductors surface superconductivity can only be observed for surface normals along high symmetry directions where atomically clean surfaces can be cleaved.Comment: Latex File, 12 pages, 2 Postscript figures, to appear in Phys. Rev. B (June 1 1996

Electron-positron pair production by linearly polarized photon in the nuclear field

Process of lepton pair production by polarized photon on nuclei can be used to measure the degree of linear polarization of high energy photon. The differential cross section and the analyzing power are calculated with taking into account higher powers of expansion on $Z\alpha$. Pure Coulomb and screened potential are considered.Comment: 12 page

Method of the photon beam linear polarization measurement using asymmetry ofthe recoil electrons in the triplet photoproduction process

We present a method of the photon beam linear polarization measurement which have been proposed and developed in Kharkov Institute of Physics and Technology and based on the using of the asymmetry of the recoil electrons in reaction g+e⁻→e⁻+e⁺+e⁻. It was found that asymmetry of the process has enough big value and weakly depend on photon energy in very wide range. So this method allows to measure the linearly polarization in the wide energy range from some tens MeV and up to TeV photon energies. The schemes of the existing polarimeters and effects distorting the measurement are considered.Розглянуто метод вимірювання лінійної поляризації фотонних пучків, якій був запропоновано в Харківському фізіко-технічному інституті. Метод засновано на вимірюванні асиметрії електронів віддачі в реакції фотоутворення електрон-позитронних пар на електронах, g+e⁻→e⁻+e⁺+e⁻. Азимутальна асиметрія даного процесу має достатньо велику величину і слабко залежить від енергії фотонів в дуже широкому діапазоні енергій, від кількох десятків МеВ і до ТеВ. Розглядаються схеми поляриметрів, що існують. Показано, що при вимірюванні поляризації необхідно брати до уваги ефекти багатократного розсіяння електронів віддачі, а також утворення d-електронів частками пари. Ці ефекти значно зменшують величину азимутальної асиметрії, що спостерігається.Рассматривается метод измерения линейной поляризации фотонных пучков, который был предложен и развит в Харьковском физико-техническом институте. Метод основан на измерении азимутальной асимметрии электронов отдачи в реакции фоторождения электрон-позитронных пар на электронах, g+e⁻→e⁻+e⁺+e⁻. Асимметрия данного процесса имеет достаточно большую величину и слабо зависит от энергии фотонов в широком диапазоне энергий. Это дает возможность измерять линейную поляризацию фотонов данным методом в диапазоне энергий от нескольких десятков МэВ до ТэВ. Рассматриваются схемы существующих поляриметров. Показано, что при измерении поляризации фотонов необходимо учитывать эффекты многократного рассеяния электронов отдачи и рождения d-электронов частицами пары. Данные эффекты существенно уменьшают наблюдаемую величину азимутальной асимметрии.Authors thank members of this group W. Briscoe, G. Feldman and G. O'Rielly for interest to the work, the given information on the first carried out experiments and fruitful discussions of the present work

Quantum Disorder and Quantum Chaos in Andreev Billiards

We investigate the crossover from the semiclassical to the quantum description of electron energy states in a chaotic metal grain connected to a superconductor. We consider the influence of scattering off point impurities (quantum disorder) and of quantum diffraction (quantum chaos) on the electron density of states. We show that both the quantum disorder and the quantum chaos open a gap near the Fermi energy. The size of the gap is determined by the mean free time in disordered systems and by the Ehrenfest time in clean chaotic systems. Particularly, if both times become infinitely large, the density of states is gapless, and if either of these times becomes shorter than the electron escape time, the density of states is described by random matrix theory. Using the Usadel equation, we also study the density of states in a grain connected to a superconductor by a diffusive contact.Comment: 20 pages, 10 figure

A dual point description of mesoscopic superconductors

We present an analysis of the magnetic response of a mesoscopic superconductor, i.e. a system of sizes comparable to the coherence length and to the London penetration depth. Our approach is based on special properties of the two dimensional Ginzburg-Landau equations, satisfied at the dual point $(\kappa = \frac{1}{\sqrt{2}}).$ Closed expressions for the free energy and the magnetization of the superconductor are derived. A perturbative analysis in the vicinity of the dual point allows us to take into account vortex interactions, using a new scaling result for the free energy. In order to characterize the vortex/current interactions, we study vortex configurations that are out of thermodynamical equilibrium. Our predictions agree with the results of recent experiments performed on mesoscopic aluminium disks.Comment: revtex, 20 pages, 9 figure

On the low temperature properties and specific anisotropy of pure anisotropically paired superconductors

Dependences of low temperature behavior and anisotropy of various physical quantities for pure unconventional superconductors upon a particular form of momentum direction dependence for the superconducting order parameter (within the framework of the same symmetry type of superconducting pairing) are considered. A special attention is drawn to the possibility of different multiplicities of the nodes of the order parameter under their fixed positions on the Fermi surface, which are governed by symmetry. The problem of an unambiguous identification of a type of superconducting pairing on the basis of corresponding experimental results is discussed. Quasiparticle density of states at low energy for both homogeneous and mixed states, the low temperature dependences of the specific heat, penetration depth and thermal conductivity, the I-V curves of SS and NS tunnel junctions at low voltages are examined. A specific anisotropy of the boundary conditions for unconventional superconducting order parameter near $T_c$ for the case of specular reflection from the boundary is also investigated.Comment: 20 page

Influence of orbital pair breaking on paramagnetically limited states in clean superconductors

Paramagnetic pair breaking is believed to be of increasing importance in many layered superconducting materials such as cuprates and organic compounds. Recently, strong evidence for a phase transition to the Fulde-Ferrell-Larkin-Ovchinnikov(FFLO) state has been obtained for the first time. We present a new theory of competing spin and orbital pair breaking in clean superconducting films or layers. As a general result, we find that the influence of orbital pair breaking on the paramagnetically limited phase boundary is rather strong, and its neglect seldom justified. This is particularly true for the FFLO state which can be destroyed by a very small orbital contribution. We discuss the situation in YBa_2Cu_3O_7 which has two coupled conducting Cu-O layers per unit cell. As a consequence, an intrinsic orbital pair breaking component might exist even for applied field exactly parallel to the layers.Comment: 19 pages, 5 figures, submitted to PR

Personal features and malevolent creativity on the example of cadets and policemen

We present and analyze the results of two empirical studies conducted in the framework of adaptation of "The malevolent creativity behavior scale" (Hao et al.) on samples of cadets-students grades 9-10 (N=89, 70-boys) and police officers (N=62, average age 26 years, men). The hypothesis that the implementation of original solutions in behavior harmful to other people is due to the interaction of aggression/its components and a set of personal characteristics was tested. The results showed: 1. a special contribution belongs to the cognitive component of aggression-hostility (Bass-Perry questionnaire), both in adolescents and adults; 2. there are age and gender features in predictors of anti-social creativity. It is shown by the example of cadets that Machiavellianism, low neuroticism, agreeableness (NEO-5 FFI) can be included in the complex of personal characteristics. Analysis of the results obtained in the sample of police officers with non-legal education showed that the combination of low hostility with high self-regulation and self-control of the individual ("self-directedness ",TCI-125) can become a resource of resistance to anti-socially directed behavior, in particular corruption