Récemment, les études des propriétés de vortex Abrikosov dans des systèmes fortement anisotropes et magnétiques ont été stimulées par la découverte des supraconducteurs à base de fer et des supraconducteurs ferromagnétiques.Dans cette thèse nous étudions la statique et la dynamique de vortex dans ces systèmes. D’abord, le problème de l'interaction de vortex avec un petit défaut a été examiné dans le cadre de la théorie de Ginzburg-Landau. Le potentiel de pinning pour une cavité cylindrique elliptique a été calculé. D'autre part, la conductivité d'un supraconducteur anisotrope à l'état mixte a été analysée en détail dans le cadre de la théorie de Ginzburg-Landau dépendant du temps.Une partie significative de la thèse est consacrée à l'étude de l'interaction entre lesondes de spin (magnons) et vortex dans les supraconducteurs ferromagnétiques.Nous avons démontré que le spectre de magnon acquiert une structure de bande en présence d'un réseau de vortex idéal. En utilisant les équations phénoménologiques de London et de Landau-Lifshitz-Gilbert, nous avons étudié les réponses ac et dc de vortex dans les supraconducteurs ferromagnétiques. Enfin, nous avons examiné l'état de vortex dans des structures hybrides supraconducteur(S)-ferromagnétique(F)(par exemple, super-réseaux FS) avec une forte dispersion spatiale de la susceptibilité magnétique. Dans ces systèmes l'électrodynamique supraconductrice peut être fortement non locale, qui mène à l'attraction des vortex et à une transition de phase du premier ordre dans la phase de vortex. / Recently, the studies of the properties of Abrikosov vortices in strongly anisotropicand magnetic media have been stimulated by the discovery of the iron-based andferromagnetic superconductors. In this thesis an analysis of vortex statics anddynamics in such systems has been carried out. Firstly, the problem of vortex pinningon a small defect has been considered. Within the Ginzburg-Landau theory thepinning potential for a cavity in the form of an elliptical cylinder has been derived.Secondly, the flux-flow conductivity of an anisotropic superconductor has beenanalyzed in detail within the time-dependent Ginzburg-Landau theory.A significant part of the thesis is devoted to the study of interplay between spinwaves (magnons) and vortices in ferromagnetic superconductors. We havedemonstrated that the magnon spectrum acquires a Bloch-like band structure in thepresence of an ideal vortex lattice. Using the phenomenological London and Landau-Lifshitz-Gilbert equations, we studied the ac and dc responses of vortices inferromagnetic superconductors. Finally, we investigated the vortex state insuperconductor-ferromagnet (FS) hybrid structures (e. g., FS superlattices) withstrong spatial dispersion of the magnetic susceptibility. In such systems thesuperconducting electrodynamics may be strongly nonlocal, which leads to theattraction of vortices and to a first order phase transition at the lower critical field.

In this thesis, intrinsic Josephson junctions, naturally formed in the strongly anisotropic high-temperature superconductor Bi2Sr2CaCu2O8 (Bi-2212), are studied experimentally. For this purpose, small mesa structures are fabricated on the surface of single crystals using micro- and nano-fabrication tools, focused ion beam is used to reduce the area of the mesa-structures down to ≈ 1 × 1 μm2. The properties of charge transport across copper-oxide layers inside the mesas are studied by intrinsic tunneling spectroscopy. Temperature, bias and magnetic field dependences of current-voltage characteristics are examined. In the main part of the thesis, the behavior of intrinsic Josephson junctions in magnetic fields B parallel to the copper-oxide planes is studied. Parallel magnetic fields penetrate the junctions in the form of Josephson vortices (fluxons). At high magnetic fields, fluxons are arranged in a regular lattice and are accelerated by a sufficient high transport current. As the fluxon lattice is moving through the mesa, it emits electromagnetic waves in the important THz frequency range. Properties of Bi-2212 mesas in this flux-flow regime are studied in this thesis. The following new observations were made during the course of this work: a crossover from thermal activation above Tc to quantum tunneling below Tc is seen in the interlayer transport-mechanism, the Fraunhofer pattern of Ic(B) is observed clearly in Bi-2212, superluminal electromagnetic cavity resonances and phonon-polaritons are observed in Bi-2212. It is argued that the employed technique for miniaturization of mesas and the obtained results can be useful for a better understanding of fundamental properties of high-temperature superconductors and for the realizations of coherent flux-flow oscillators and coherent phonon-polariton generators in the important THz frequency range. / At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Manuscript.

In this thesis, the tunneling between individual atomic layers in structures of Bi2Sr2CaCu2O8+x based high-temperature superconductors are experimentally studied employing the intrinsic Josephson effect. A special attention is paid to the fabrication of small mesa structures using micro and nanofabrication techniques. In the first part of the thesis, the periodic Fraunhofer-like modulation of the critical current of the junctions as a function of in-plane magnetic field is investigated. A transition from a modulation with a half flux quantum to a flux quantum periodicity is demonstrated with increasing field and decreasing junction length. It is interpreted in terms of the transformation of the static fluxon lattice of stacked, strongly coupled intrinsic Josephson junctions and compared with theoretical predictions. A fluxon phase diagram is constructed.Numerical simulations have been carried out to complement the experimental data. In the second part of the thesis, different resonant phenomena are studied in the dynamic flux-flow state at high magnetic fields, including Eck-resonances and Fiske steps. Different resonant modes and their velocities, including superluminal modes, are identified. In the third part, different experiments attempting to detect radiation from small mesa structures using different setups based on hot-electron bolometer mixers and calorimeters are described. No distinct radiation with emission powers higher than about 500pW could be detected. Furthermore, the interaction with external GHz-radiation is studied. Resonances attributed to an induced flux-flow are observed, and the reflectivity of the sample can be tuned by switching mesas between the superconducting and quasiparticle state. In the last part, the resistive switching of mesas at high bias is studied. It is attributed to a persistent electrical doping of the crystal. Superconducting properties such as the critical current and temperature and the tunneling spectra are analyzed at different doping states of the same sample. The dynamics of the doping is studied, and attributed to two mechanisms; a charge-transfer effect and oxygen reordering

The rapid depletion of hydrocarbon fields around the world has led the industry to search for these resources in ever increasing water depths. In this context, the large diameter (D > 100mm) vertical riser has become a subject of great interest. In this research work, a major investigation was undertaken to determine the two phase flow hydrodynamics in a 254mm vertical riser. Two types of experiments were performed for range of air-water superficial velocities. The first experimental campaign addresses the issue of the two gas injector’s performances (conventional vs. novel design gas injector) in the large diameter vertical riser. The experimental results show that the novel design gas injector should be the preferential choice. The second set of the experimental work investigates the two phase flow hydrodynamics in the vertical riser in detail. The two phase flow patterns and their transitions were identified by combination of visual observations and statistical features. Based on the results, the experimental flow regime map was developed and compared with the existing vertical upflow regime maps/models. None of the flow regime transition models adequately predicted the flow regimes transitions in large diameter vertical risers as a whole. In this regard, the Taitel et al. (1980) bubble to slug flow transition model has been modified for large diameter vertical upflow conditions, based on the physical mechanism observed. The general trends of modified criteria agreed well with the current and other large diameter experimental results. The effect of upstream conditions on the vertical riser flow behaviour was also investigated in detail by two different inlet configurations (i) near riser base injection and (ii) upstream flowline injection. It was found that no significant differences exist in flow behaviour at low air-water superficial velocities for both the inlet configuration, at high air-water superficial velocities, the intermittent flow behavior in flowline influences the riser flow pattern characteristics and thereby controls the riser dynamics. It is found that liquid slugs from the flowline naturally dissipate to some extent in the riser as a consequence of compression of succeeding bubble that rapidly expands and break through the liquid slug preceding it when it enters the riser. The experimental work corroborates the general consensus that slug flow does not exist in large diameter vertical upflow condition. Experimental data has been further compared to increase the confidence on the existing two phase flow knowledge on large diameter vertical riser: (a) by comparing with other experimental studies on large diameter vertical upflow in which generally, a good agreement was found, (b) by assessing the predictive capability of void fraction correlations/pressure gradient methods. The important implication of this assessment is that the mechanistic approach based on specific flow regime in determining the void fraction and pressure gradient is more successful than conventional empirical based approaches. The assessment also proposes a proposed set a of flow regime specific correlations that recommends void fraction correlations based on their performances in the individual flow regimes. Finally, a numerical model to study the hydrodynamic behaviour in the large diameter horizontal flowline-vertical riser system is developed using multiphase flow simulator OLGA. The simulated results show satisfactory agreement for the stable flows while discrepancies were noted for highly intermittent flows. The real time boundary application was partially successful in qualitatively reproducing the trends. The discrepancies between the predicted results and experimental data are likely to be related to the incorrect closure relations used based on incorrect flow regimes predictions. The existence of the multiple roots in the OLGA code is also reported for the first time.