In this report the analysis of microstrip electrodynamic structures on basis of high-temperature superconductors is carried out and a mathematical model of microstrip devices with lumped and distributed nonlinear properties is created. For this purpose nonlinear integral equations method and method of moments are used. In the issue of the work a SHF filter based on the equivalent circuit of elements with lumped parameters is also studied. It is ascertained that the received mathematical model allows to achieve more proper results of modeling on compensation of variation of current-density distribution nearby the edges of conductor break.

The class of high Tc superconductors share one common structural aspect, the existence of planes of copper and oxygen ions. These planes are thought to be the source of the superconducting behaviour. They can be represented as a two-dimensional lattice of ions, which facilitates their study using numerical models. One such model is the t − J model. In most studies utilising numerical models, the planes have been considered isotropic. However, recent analysis of cuprate structure has illustrated that this may not be representative of the copper oxide planes. A number of cuprate structures exhibit different phases in which the planes are not isotropic, such as the low temperature orthorhombic and low temperature tetragonal phases. This work will examine the effects of introducing anisotropy into the t − J model in order to understand how these phases affect the results gained from numerical studies. / x, 89 leaves : ill. ; 29 cm.

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Dans les dispositifs électronique, il est prochainement attendu que la réduction de la taille des composant atteingne prochainement la limite quantique. De ce fait, manipuler l'information quantique apparait comme un nouveau challenge. Les Qubits supraconducteurs basé sur la physique du solide et les Jonctions Josephson sont des systèmes prometteurs qui profitent des avantage des technologies de la micro-électronique. Toutefois, le temps de décohérence des états quantique est encore un facteur limitant. Cette limitation est généralement attribuée à la faible qualité cristalline des matériaux utilisés (défauts cristallins, impuretés). La technique d'épitaxie par jets moléculaires a été utilisé pour la croissance de couches minces de rhénium de haute qualité cristalline sur des substrat de saphir dans un environnement Ultra Haut Vide. Le misfit existant entre les réseaux cristallins du rhénium et du saphir est suffisamment bas pour permettre une croissance épitaxiale du rhénium sur le saphir, mais également une croissance d'une barrière tunnel en oxyde d'aluminium monocristallin sur la couche de rhénium elle-même. Afin d'améliorer la qualité cristallographique de la couche de rhénium, des simulations et de nombreuses techniques de caractérisation ont été utilisées. Puis les propriétés supraconductrices des films de rhénium ont été étudié à des températures ultra basses afin de comparer ces propriétés à la qualité cristallographique de nos films. / In electronic devices, it is expected that the quantum limit will soon be reached with decreasing system size. Therefore, manipulating quantum information appears as a new challenge. Solid state Qubits based on superconducting Josephson junction are promising systems which take advantage of microelectronics technology. However, decoherence time of the quantum states is still a limiting factor. This has been generally ascribed to the poor crystallographic quality of the materials used so far (crystallographic defects, impurities). The Molecular Beam Epitaxy (MBE) technique may be used to grow rhenium (Re) films of high quality on sapphire substrates in an Ultra High Vacuum (UHV) environment. So far, the misfit between Re and sapphire is low enough to permit the growth of a single crystal aluminium oxide thin film on top of the Re layer. In order to improve the crystallographic quality of the Re film, some simulations and several characterizations techniques have been used. Then, the superconducting properties of rhenium films have been studied at Ultra Low Temperature in order to compare with their crystallographic qualities.

The thesis work discusses the design, realization, characterization and operation of a two-qubit processor implemented using capacitively coupled tunable superconducting qubits of the Transmon type. Each qubit can be manipulated and read out individually using a non-destructive single-shot readout. In addition, a universal-two qubit gate can be implemented using the interaction between the qubits. The processor implements therefore all basic building blocks of a universal two-qubit quantum processor. Using it, we implement the universal square root of iSWAP two-qubit gate, characterizing the gate operation by quantum process tomography and obtaining a gate fidelity of 90 %. We use this gate to create entangled two-qubit Bell states and perform a test of the CHSH Bell inequality, observing a violation of the classical boundary by 22 standard eviations after correcting for readout errors. Using the implemented two-qubit gate, we run the so-called Grover search algorithm: For two-qubits, this algorithm finds among four elements {00, 01, 10, 11} the one element y that solves a search problem encoded by a function f for which f(y) = 1 and f(x != y) = 0. Our implementation retrieves the correct answer to the search problem after a single evaluation of the search function f(x), with a success probability between 52 % and 67 %, therefore outperforming classical algorithms that are bound to a success probability of 25 %. This constitutes therefore a proof-of-concept of the quantum speed-up for superconducting quantum processors. Finally, we propose a scalable architecture for a superconducting quantum processor that can potentially overcome the scalability issues faced by today's superconducting qubit architectures.

La récente découverte de supraconductivité dans les pnictures de fer ouvre un nouveau champ d'investigation du mécanisme d'appariement des électrons donnant lieu à des hautes températures critiques. Dans ces systèmes, le magnétisme et la supraconductivité sont des phases en compétition, où le dopage x déstabilise l'ordre magnétique au profit de l'ordre supraconducteur. Un régime de coexistence entre ces deux ordres est présent pour une certaine gamme de dopage dans le composé Ba(Fe1-xCox)2As2, que nous avons étudié par diffusion inélastique de la lumière. Nous nous sommes intéressés à l'interaction entre les degrés de liberté structuraux, magnétiques et électroniques. L'étude des excitations vibrationnelles du cristal montre le fort couplage spin-phonon, à travers le dédoublement d'un mode de phonon dans les plans fer-arsenic amplifié par l'anisotropie planaire des degrés de spin, et le fort couplage électron-phonon, via l'asymétrie significative du mode de phonon de l'arsenic. L'évolution du continuum des excitations électroniques à travers la transition magnétique et supraconductrice traduit, d'une part, l'ouverture du gap d'onde de densité de spin, et d'autre part, que le gap supraconducteur est de symétrie s-anisotrope. Après avoir identifié séparément l'impact de chacune des transitions magnétique et supraconductrice sur nos spectres, nous nous sommes intéressés au régime de coexistence entre les deux ordres. Nos résultats illustrent une compétition pour les mêmes états électroniques au niveau de Fermi entre ces deux ordres, qui s'établissent sur différentes zones de la surface de Fermi.

This thesis is devoted to studies of high temperature superconductors and related materials using the angle-resolved photoemission spectroscopy (ARPES). Though there is no accepted theory of superconductivity, encompassing high-$T_{\\rm c}$ materials, there is enough evidence to believe that superconductivity can always be interpreted as stemming from pairing of electrons by interaction with bosons, and $T_{\\rm c}$ is determined by effectiveness of such a pairing. ARPES, owing to the possibility of recording energy- and momentum-resolved electronic spectrum, is a powerful probe of the normal-state electronic structure, which is an important prerequisite for the superconductivity, and implications of the electron pairing, such as emergence of the superconducting gap and finer features below $T_{\\rm c}$. Based on ARPES data one can quantify the electronic interactions by analysis of kinks in the dispersion curves, spectral line widths etc. In current work new methods of ARPES data analysis were developed and applied to the spectra taken from cuprate and iron-based high-$T_{\\rm c}$. The possibility to analyze the macroscopic response of solids in the normal state as well as in the superconducting and charge-density-wave phases basing on the experimentally measured renormalized band dispersion and anisotropic superconducting and charge-density-wave gap was shown. The thesis consists of five parts. Part 1 introduces the employed notions of electrons in solids and methods of their investigation. Part 2 describes the Voigt fitting procedure, allowed for purification of the spectra from resolution effects, and, consequently, for determination of the quasiparticle scattering rate with enhanced precision. In Part 3 the calculation of the temperature-dependent Hall coefficient in the charge-density-wave-bearing 2H-TaSe$_2$ from the band dispersion, measured in ARPES, is presented, and comparison to the independent magnetotransport measurements is shown. The extraction of the band dispersion of Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$ and LiFeAs from ARPES data can be found in Part 4. Agreement with Hall effect measurements on the same samples is demonstrated. Part 5 introduces the extraction of the momentum-dependent superconducting gap in iron arsenides from fitting of ARPES spectra to Dynes function. The superfluid density was calculated from the band dispersion and the superconducting gap, measured in ARPES, and compared to the ones measured by different techniques.

Pinning landscapes in modern second generation coated conductors are excellent candidates for studies of vortex pinning. The ability to produce engineered defects in thin films of high temperature superconductors allows one to investigate representative distinct pinning sites, with the objective of understanding how different pinning centers contribute, compete and evolve under varying conditions of magnetic field strength and orientation, and temperature.New contact-free methods were developed specifically to investigate this system in new ways, especially the dependence of the critical current density Jc on orientation of the magnetic field. A superconducting quantum interference device (SQUID)-based magnetometer was used to determine angular critical current density profiles. The induced currents produced in contact-free methods allow one to investigate a range of temperatures that is difficult to access by traditional transport measurements.Materials with three distinctive pinning landscapes were investigated: Specifically, samples were studied that were dominated by columnar defects, by isotropic defects, or a mixture of these two types of pins. These studies over an expanded temperature-field-orientation phase-space clearly show competition between not only strong and weak pinning centers, but also between the angularly selective and nonselective pinning. This evidence is seen in critical current density profiles, the α [alpha]-values describing the falloff of Jc with magnetic field, and matching field effects in the three samples studied.

High-quality platelet single crystals of Tl₂Ba₂CuO₆±δ (Tl-2201) have been grown using a novel time-varying encapsulation scheme, minimizing the thallium oxide loss that has plagued other attempts and reducing cation substitution. This encapsulation scheme allows the melt to be decanted from the crystals, a step previously impossible, and the remaining cation substitution is homogenized via a high-temperature anneal. Oxygen annealing schemes were developed to produce sharp superconducting transitions from 5 to 85 K without damaging the crystals. The crystals' high homogeneity and high degree of crystalline perfection are further evidenced by narrow rocking curves; the crystals are comparable to YSZ-grown YBa₂Cu₃O₆₊δ by both metrics. Electron probe microanalysis (EPMA) ascertained the crystals' composition to be Tl₁.₉₂₀₍₂₎Ba₁.₉₆₍₂₎Cu₁.₀₈₀₍₂₎O₆₊δ; X-ray diffraction found the composition of a Tc = 75 K crystal to be Tl₁.₉₁₄₍₁₄₎Ba₂Cu₁.₀₈₆₍₁₄₎O₆.₀₇₍₅₎, in excellent agreement. X-ray refinement of the crystal structure found the crystals orthorhombic at most dopings, and their structure to be in general agreement with previous powder data. Cation-substituted Tl-2201 can be orthorhombic, orthorhombic crystals can be prepared, and these superconduct, all new results. X-ray diffraction also found evidence of an as yet unidentified commensurate superlattice modulation. The Tl-2201 crystals' electronic structure were studied by X-ray absorption and emission spectroscopies (XAS/XES). The Zhang-Rice singlet band gains less intensity on overdoping than expected, suggesting a breakdown of the Zhang-Rice singlet approximation, and one thallium oxide band does not disperse as expected. The spectra correspond very closely with LDA band structure calculations, and do not exhibit the upper Hubbard bands arising from strong correlations seen in other cuprates. The spectra are noteworthy for their unprecedented (in the high-Tc cuprates) simplicity. The startling degree to which the electronic structure can be explained bodes well for future research in the cuprates. The overdoped cuprates, and Tl-2201 in particular, may offer a unique opportunity for understanding in an otherwise highly confusing family of materials.