京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22238号 / 理博第4552号 / 新制||理||1654(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 松田 祐司, 教授 石田 憲二, 教授 寺嶋 孝仁 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22685号 / 理博第4626号 / 新制||理||1665(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)准教授 前里 光彦, 教授 吉村 一良, 教授 有賀 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 新制・課程博士 / 博士(理学) / 甲第22989号 / 理博第4666号 / 新制||理||1669(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 石田 憲二, 教授 柳瀬 陽一, 教授 前野 悦輝 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Titanium is one of the earth-abundant elements, and its oxides including titanium dioxide (TiO2) and strontium titanium oxide (SrTiO3) are widely used in technologies of electronics, energy conversion, catalysis, sensing, and so on. Generally, the Ti ions in these compounds have a valence of 4+ with the outer shell electron configuration of 3d0. In this thesis, we explore interface and titanite containing Ti3+ ions with 3d1 itinerate electrons, which we believe open new doors towards some new titanite-based technologies. In the first part of this thesis (Chapter 3), we will discuss the nanoscale chemical and valence evolution at a metal/oxide interface: Ti/SrTiO3. In many devices, metal-oxide interfaces are ubiquitous and play important roles in the performance of a wide range of electronic and optoelectronic devices. This motivated us to examine the microscopic structure of the interfaces between strontium titanium oxide and metals. In this work, one unit cell of cubic perovskite Ti2O3 was observed at the Ti/SrTiO3 interface, and oxygen diffusion depth of ~3.2 nm was observed in the sample fabricated at room temperature. Meanwhile, oxygen vacancy domains in the SrTiO3 substrates was observed and characterized by low angle annular dark field (LAADF) imaging and electron energy loss spectra (EELS). In the main part of this thesis, we will focus on the structure and physical properties of Ti2O3, a titanite which has received less attention so far in the research community. Different from TiO2 and SrTiO3, Ti2O3 has a much narrower band-gap (~0.1 eV), and we will discuss some preliminary results of its physical properties and potential applications. In Chapter 4, we will discuss the photothermal application and mid-infrared photodetectors using Ti2O3 nanoparticles based on its ultra-narrow bandgap. Photo-thermal effect via a Ti2O3/membrane structure is further applied to seawater desalination. A high temperature of 70 °C was achieved when this Ti2O3/membrane double layer structure floating on top surface of water subjected to the white light illumination of 7 kW/cm2. Furthermore, room temperature mid-infrared (10 μm) photodetectors based on Ti2O3/graphene hybrid structure was fabricated and studied. The photoresponsivity of this hybrid device, operated from 4.5 to 10 μm, is above ~ 100 A/W, which, to our knowledge, is the highest value for the mid-infrared photodetectors operating in the photocurrent (PC) mode. In chapter 5, structure, optical, transport properties of Ti2O3 epitaxial thin films on sapphire fabricated by pulsed laser deposition (PLD) will be discussed. By tailoring growth conditions, two different: trigonal and orthorhombic, of Ti2O3 were stabilized on Al2O3 substrates. More interestingly, the orthorhombic Ti2O3 has never been reported, and, moreover, superconductivity (~8 K) and high temperature ferromagnetism (up to 700 K) was discovered in this new stabilized phase. More details of the physical properties of Ti2O3 will be discussed in the following chapters of this dissertation.

In this thesis, the single-level correlated quantum dot attached to two BCS superconducting leads is analyzed. A difference in the superconducting phases of the leads induces the DC Josephson supercurrent in the junction. In this setup, the influence of asymmetrical dot-lead couplings on transport properties is clarified analytically. The coupling asymmetry and the phase difference can be combined into one function, which allows us to calculate physical properties of a system with coupling asymmetry from the properties of its effective symmetric counterpart. The coupling asymmetry turns out to be an important parameter which influences the position of the 0 − �෰ quantum phase transition even in the strongly correlated Kondo regime. Further, this thesis contributes to the interpretation of an AC Josephson current measurement, in which a surprising drop in the amplitude was observed in the Kondo regime. The experimental setup is characterized using numerical renormalization group calculations of the equilibrium many-body spectra. Possible quantum-point-contact- based interpretations are discussed. Although a drop in the AC Josephson current at the experimental bias voltage is also expected in a quantum point contact, we conclude that the physical mechanisms causing it in the quantum dot system are likely not...

Supraleitung in Graphit ist kein neues Thema. Dieser Effekt wurde bereits in den 1960er Jahren in Interkalationsverbindungen von Graphit gefunden. Die Supraleitung in reinem Graphit wurde bereits vor etwa 50 Jahren beschrieben. Kürzlich wurden in zweischichtigem Graphen, in dem die Graphenschichten um einen 'magischen' Winkeln um die c Achse verdreht wurden, flache Bänder in der elektronischen Bandstruktur nachgewiesen, welche mit der Entstehung von Supraleitung zusammenhängen. Wir haben die elektrischen Transporteigenschaften in Graphitproben mit unterschiedlichen Elektrodenkonfigurationen untersucht. Wir haben den elektrischen Widerstand von hochgeordnetem natürlichem und synthetischem Graphit mit Elektroden auf der Oberseite der ab Basalebene und auch parallel zur c Achse mit hoher Präzision gemessen und den Einfluss der hochleitenden Stapelfehler untersucht, an denen, eingebettet zwischen den kristallinen Graphitschichten, 2D-Grenzflächen entstehen, die ebenfalls flache Bänder aufweisen. Die Existenz einer gut geordneten rhomboedrischen Graphitphase in allen gemessenen Proben wurde durch Röntgenbeugungsmessungen nachgewiesen. Die Grenzflächen mit der hexagonalen Phase stellen laut theoretischer Vorhersagen einen möglichen Ursprung für die Hochtemperatursupraleitung dar. Die experimentellen Ergebnisse liefern eindeutige Beweise für körnige Supraleitung in diesen Materialien, z. B. einen schrittweisen Temperaturübergang bei ~ 350 K, magnetische Irreversibilität, Zeitabhängigkeit nach einer Feldänderung, die mit dem eingeschlossenen Fluss und Flusskriechen übereinstimmt, und den teilweise abgestoßenen magnetischen Fluss, welcher in Magnetisierungsmessungen beobchtet werden kann. Die Lokalisierung der körnigen Supraleitung an diesen 2D-Grenzflächen verhindert die Beobachtung widerstandsfreier elektrischer Ströme oder eines vollständigen Meißner-Zustands. Der Grund ist, dass die körnige Supraleitung in abgegrenzten Regionen an den Grenzflächen entsteht, welche in eine Multigraphen-Halbleitermatrix eingebettet sind. In dieser Arbeit wird eine detaillierte Untersuchung des Magnetowiderstands in verschiedenen Arten von Graphitproben bei niedrigen und hoch gepulsten Magnetfeldern vorgestellt. / Superconductivity in graphite is not a new topic. Its existence goes back to the 1960s when this effect was found in intercalation compounds of graphite. Superconductivity in pure graphite was reported already around 50 years ago and recently proved in bi-layer graphene, related to 'magic' angles between the graphene layers, twisted around the c axis, with the electronic band structure exhibiting flat bands. We have studied electrical transport properties in graphite samples with different electrode configurations. Measuring with high precision, the electrical resistance of highly ordered natural and synthetic graphite, with electrodes placed on the top of the ab basal plane, and also parallel to the c axis, we investigated the influence of the highly conducting stacking faults, referred as 2D interfaces, embedded between the crystalline regions of graphite, which also exhibit flat bands. The existence of well ordered rhombohedral graphite phase in all measured samples has been proved by x-ray diffraction measurements, suggesting its interfaces with the hexagonal phase as a possible origin of high-temperature superconductivity, predicted by theoretical studies. The results provide clear evidence of granular superconductivity, e.g., a step-like transition in temperature at ~ 350 K, magnetic irreversibility, time dependence after a field change, consistent with trapped flux and flux creep, and the partial magnetic flux expulsion from magnetization measurements. The localization of the granular superconductivity at these 2D interfaces prevents the observation of a zero resistance state or a full Meissner state. The reason is that the superconducting distribution is a mixture of superconducting patches at the interfaces, and they are embedded in a multigraphene semiconducting matrix. A detailed study of the magnetoresistance in different kinds of graphite samples at low and high-pulsed magnetic fields is presented in this work.

This master thesis is focused on description and research of electromagnetic waves in plasma state. Some simple cases of no-loss mode distribution of electromagnetic waves in plasma are known, for example around the coaxial cable. In other words, the properties of superconducting state in materials are shown. This view of plasma properties can significantly help to clarify observed phenomena in experimental plasma research or to outline new trends in plasma usage in this mode. The introduction and the theoretical parts describe the known theory related to the propagation of electromagnetic waves in a non-homogeneous or anisotropic environment, in the next parts of the thesis the mathematical model of the solved problem of wave propagation in plasma is mentioned and the design and realization of the experiment is followed. The model includes processing of Maxwell's reduced equations in Haeviside notation for the state of matter referred to as plasma, the design of a model for numerical modeling and analysis, and the design of a simple experiment to verify numerically analyzed results.

This report explains how an SMES is operated and how SMES systems could be used to increase the efficiency of the CERN Large Hadron Collider (LHC) and the Future Circular Collider (FCC) as well as to reduce the very high power needs of a future Muon Collider (MC). The performance of SMES for other applications and late developments of the technique will also be described.

The Bi2Sr2CaCu2O7+d, i.e. Bi2212 phase of bismuth derived high temperature superconductors (HTS), powder precursor were synthesized via sol – gel technique using ethylendiamintetraacetic acid (Chelaton II) as a chelating agent. Metal nitrate’s solutions were mixed with EDTA suspension. The pH value was adjusted to 9 by NH4OH by reason forming of stable metal’s complexes. The mixture was heated to 80 °C for gelation. Solution taken before solid gel was form is used for preparation of Bi2212 layer on to a-Al2O3 surface via spin coating deposition’s technique. Reactive powder used for bulk sample preparation was made by calcination (800 °C) of pyrolyzed xerogel (500 °C). Sintering in oxygen atmosphere was proceeding at temperature from 850 to 880 °C. Bulk sample properties were compared with sample prepared by common ceramic method. Simultaneous TG-DTA, IR spectroscopy and heating microscopy were used for sample characterization. Furthermore, construction of furnace for sintering in O2 atmosphere was described.

Des états électroniques localisés apparaissent dans les liens faibles entre électrodes supraconductrices : les états d’Andreev. Les expériences présentées dans cette thèse explorent les propriétés de cohérence quantique de ces états, en utilisant comme liens faibles des contacts à un atome entre des électrodes d’aluminium. Les contacts atomiques sont intégrés dans une cavité microonde qui permet à la fois de les isoler et de les sonder.Dans une première série d’expériences, il est montré qu’on peut utiliser les états d’Andreev pour définir un bit quantique, le « qubit d’Andreev », qu’on contrôle à l’aide d’impulsions micro-onde.Les mesures des temps de vie de cohérence de ce qubit sont analysées en détail.Dans une deuxième série d’expérience,l’interaction entre le qubit d’Andreev et le résonateur micro-onde est utilisée pour quantifier le nombre de photons présents dans le résonateur en fonction de la puissance d’impulsions microonde à sa fréquence propre.Enfin, des sauts quantiques et des sauts de parités ont observés dans des mesures continues de l’état du qubit d’Andreev. / Localized electronic states, called Andreev bound states, appear in weak-links placed between superconducting electrodes. The experiments presented in this thesis explore the coherence properties of these states. Single atom contacts between aluminum electrodes are used as weak links. In order to isolate and probe these states, the atomic contacts are integrated in amicrowave cavity.In a first series of experiments, it is shown that Andreev states can be used to define a quantumbit, “the Andreev qubit”, which is controlled using microwave pulses.Measurements of the lifetime and coherence time of this qubit are thoroughly analyzed.In a second series of experiments, the interaction between the Andreev qubit and the microwave cavity are used to determine the number of photons present in the cavity as a function of the power of microwave pulses at its eigenfrequency.Finally, quantum and parity jumps are observed in continuous measurements of the state of the Andreev dot.