Ce manuscrit présente une étude expérimentale de phase isolante non-conventionnelle, l'isolant d'Anderson, induit par le désordre, l'isolant de Mott, induit par les interactions de Coulomb, et les isolants topologiques.Dans une première partie du manuscrit, je décrirais le développement d'une méthode pour étudier la réponse de charge de nanoparticules par Microscopie à Force Electrostatique (EFM). Cette méthode a été appliquée à des nanoparticules de magnétite (Fe3O4), un matériau qui présente une transition métal-isolant, i.e. la transition de Verwey, lors de son refroidissement en dessous d'une température TV~120 K.Dans une seconde partie, ce manuscrit présente une étude détaillée de l'évolution de la densité d'états au travers de la transition métal-isolant entre un isolant de type Anderson-Mott et une phase métallique dans le matériau SrTiO3, et ceci, en fonction de la concentration de dopants, les lacunes d'oxygènes. Nous avons trouvé que dans un dispositif memoresistif de type Au-SrTiO3-Au, la concentration de dopants pouvait être ajustée par migration des lacunes d'oxygènes à l'aide d'un champ. Dans cette jonction tunnel, l'évolution de la densités d'états au travers de la transition métal-isolant peut être étudiée de façon continue. Finalement, dans une troisième partie, le manuscrit présente le développement d'une méthode pour la microfabrication d'anneaux de Aharonov-Bohm avec l'isolant topologique, Bi2Se3, déposée par épitaxie à jet moléculaire. Des résultats préliminaires sur les propriétés de transport quantique de ces dispositifs seront présentés. / This manuscript presents an experimental study of unconventional insulating phases, which are the Anderson insulator, induced by disorder, the Mott insulator, induced by Coulomb interactions, and topological insulators.In a first part of the manuscript, I will describe the development of a method to study the charge response of nanoparticles through Electrostatic Force Microscopy (EFM). This method has been applied to magnetite Fe3O4 nanoparticles, a material that presents a metal-insulator transition, i.e. the Verwey transition, upon cooling the system below a temperature Tv=120K. In a second part, this manuscript presents a detailed study of the evolution of the Density Of States (DOS) across the metal-insulator transition between an Anderson-Mott insulator and a metallic phase in the material SrTiO3 and this, as function of dopant concentration, i.e. oxygen vacancies. We found that in this memristive type device Au-SrTiO3-Au, the dopant concentration could be fine-tuned through electric-field migration of oxygen vacancies. In this tunnel junction device, the evolution of the DOS can be followed continuously across the metal-insulator transition. Finally, in a third part, the manuscript presents the development of a method for the microfabrication of Aharonov-Bohm rings with the topological insulator material, Bi2Se3, grown by molecular beam epitaxy. Preliminary results on the quantum transport properties of these devices will be presented.

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Bismuth selenide belongs to a class of topological insulators---materials characterized by a intriguing electronic band structure, with a characteristic Dirac conical band on the surface. In this master thesis, the optical response of this material is explored in the infrared spectral range and in a broad range of magnetic fields. We mainly focus on the absorption of light due to free charge carriers having, when the magnetic field is applied, a form of cyclotron resonance. We find that the experimentally observed response is consistent with expectations for massive electrons in bulk rather than massless particles on the surface.

The accident at the Fukushima Daiichi nuclear power plant has shown us that there may be situations where the applied technology will not be able to successfully cool the reactor core. These situations may occur when more elements such as supply of energy to power the pumps and diesel generators are destroyed for example by tsunami or earthquake, or other not expected natural disasters. The inability of the residual heat removal leads to the melting of core, relocation to the bottom of reactor pressure vessel (RPV) and failure of RPV. Result of this accident may be containment failure and leakage of fission products into the environment. One way to prevent this scenario may be a passive system called IVR (In-Vessel Retention) by using external cooling of RPV that retains melted core in. This system counts with flooding of RPV´s shaft by water. After natural circulation of water provides the heat transfers from the wall of RPV. The applicability of IVR for VVER 1000 reactors is still in the course of research. However it´s already clear that the submersion of RPV shaft by water will not sufficient. Other elements as suitable insulation and RPV coating which provides a more intensive heat transfer from the walls of RPV will be needed.

Cette thèse décrit la réalisation et l’étude de réseaux bidimensionnels de résonateurs supraconducteurs en nid d’abeille. Ce travail constitue un premier pas vers la simulation de systèmes de la matière condensée avec des circuits supraconducteurs. Ces réseaux sont micro-fabriqués et sont constitués de plusieurs centaines de sites. Afin d’observer les modes propres qui y apparaissent dans une gamme de fréquence entre 4 et 8 GHz, nous avons mis au point une technique d’imagerie. Celle-ci utilise la dissipation locale créée par un laser avec lequel nous pouvons adresser chaque site du réseau. Nous avons ainsi pu mesurer la structure de bande et caractériser les états de bord de nos réseaux. En particulier, nous avons observé les états localisés qui apparaissent à l'interface entre deux isolants de Semenoff ayant des masses opposées. Ces états, dits de Semenoff, sont d'origine topologique. Nos observations sont en excellent accord avec des simulations électromagnétiques ab initio. / This thesis describes the realization and study of honeycomb lattices of superconducting resonators. This work is a first step towards the simulation of condensed matter systems with superconducting circuits. Our lattices are micro-fabricated and typically contains a few hundred sites. In order to observe the eigen-modes that appear between 4 and 8 GHz, we have developed a mode imaging technique based on the local dissipation introduced by a laser spot that we can move across the lattice. We have been able to measure the band structure and to characterize the edge states of our lattices. In particular, we observe localized states that appear at the interface between two Semenoff insulators with opposite masses. These states, called Semenoff states, have a topological origin. Our observations are in good agreement with ab initio electromagnetic simulations.

The present work covers the fabrication and electrical and magnetic investigation of LaNiO3- and LaMnO3- based superlattices (SL). In recent years, several interesting theoretical predictions have been made in these SLs, for example, Mott insulators, metal-insulator transitions, superconductivity, topological insulators, and Chern insulators. Motivated by the promising theoretical predictions, four kinds of SLs with different designed structures and orientations were systematically studied in this thesis. The samples were grown by pulsed laser deposition with in-situ reflection high-energy electron diffraction to monitor the two-dimensional layer-by-layer growth process. In order to ensure the high-quality of SLs, growth parameters were optimised. Characteristic methods like X-ray diffraction, atomic force microscopy, and transmission electron microscopy were used. These measurements proved the high-quality of the SLs and provided the basis for electrical and magnetic measurements. The first studied SL is the (001)-oriented LaNiO3/LaAlO3 SL, which was predicted as a superconductor in theory. Temperature-dependent resistivity measurements revealed a metal-insulator transition by lowering the dimensionality of the LaNiO3 layers in the SLs from three dimensions to two dimensions. The second studied SL is the (111)-oriented LaNiO3/LaAlO3 SL, which was predicted as a topological insulator in theory. The polarity-controlled conductivity was observed and the intrinsic conductivity mechanisms were discussed by means of appropriate modeling. The third studied SL is LaMnO3/LaAlO3 SL, which was predicted as a Chern insulator in theory. By lowering the temperature, a paramagnetic-ferromagnetic phase transition and a thermal activated behavior were observed in the SLs. The last studied SL is the LaNiO3/LaMnO3 SL, in which an exchange bias effect was expected. The studies reveal the exchange bias exists in three kinds of SLs with different orientations.

This thesis aims to present a method for detection of faults (burn marks) on insulator using only image processing algorithms. It is accomplished by extracting the insulator from the background image and then detecting the burn marks on the segmented image. Apart from several other challenges encountered during the detection phase, the main challenge was to eliminate the connector marks which might be detected as burn-marks. The technique discussed in this thesis work is one of a kind and not much research has been done in areas of burn mark detection on the insulator surface. Several algorithms have been pondered upon before coming up with a set of algorithms applied in a particular manner. The first phase of the work emphasizes on detection of the insulator from the image. Apart from pre-processing and other segmentation techniques, Symmetry detection and adaptive GrabCut are the main algorithms used for this purpose. Efficient and powerful algorithms such as feature detection and matching were considered before arriving at this method, based on pros and cons. The second phase is the detection of burn marks on the extracted image while eliminating the connector marks. Algorithms such as Blob detection and Contour detection, adapted in a particular manner, have been used for this purpose based on references from medical image processing. The elimination of connector marks is obtained by applying a set of mathematical calculations. The entire project is implemented in Visual Studio using OpenCV libraries. Result obtained is cross-validated across an image data set.

One of the main features of topological phases is the presence of robust boundary states that are protected by a topological invariant. Famous examples of such states are the chiral edge states of a Chern insulator, the helical edge states of a two-dimensional Z2 insulator, and the Fermi arcs of Weyl semimetals. Despite their omnipresence, these topological boundary states can typically only be theoretically investigated through numerical studies due to the lack of analytical solutions for their wave functions. In the rare cases that wave-function solutions are available, they only exist for simple fine-tuned systems or for semi-infinite systems. Exact solutions are, however, common in the field of flat bands physics, where they lead to an understanding of the bulk bands rather than the boundary physics. It is well known that fully-periodic lattices with a frustrated geometry host localized modes that have a constant energy throughout the Brillouin zone. These localized modes appear due to a mechanism referred to as destructive interference, which leads to the disappearance of the wave-function amplitude on certain lattice sites. Making use of this mechanism, it is shown in this licentiate thesis that exact wave-function solutions can also be found on d-dimensional geometrically frustrated lattices that feature (d − 1)-dimensional boundaries. These exact solutions localize to the boundaries when the frustrated lattice hosts a topological phase and correspond to the robust, topological boundary states. This licentiate thesis revolves around the publication, which describes the method to finding these exact, analytical solutions for the topological boundary states on geometrically frustrated lattices, which was authored by the author of this licentiate thesis together with Maximilian Trescher and Emil J. Bergholtz and published in Physical Review B on August 30, 2017 with the title Anatomy of topological surface states: Exact solutions from destructive interference on frustrated lattices. An introduction is given on topological phases in condensed matter systems focussing on those models of which explicit examples are given in the paper: two-dimensional Chern insulators and three-dimensional Weyl semimetals. Moreover, by making use of the kagome lattice as an example the appearance of localized and semi-localized modes on geometrically frustrated lattices is elaborated upon. The chapters in this licentiate thesis thus endeavor to provide the reader with the proper background to comfortably read, understand, place into context and judge the relevance of the work in the accompanying publication. The licentiate thesis finishes with an outlook where it is discussed that the method presented in the paper can be generalized to an even larger class of lattices and can also be applied to find exact solutions for higher-order topological phases such as corner and hinge states.

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