L'étude de l'état isolant de Mott est un des domaines très actif de la recherche en matière condensée car les fortes corrélations qui en sont à l'origine donnent naissance à des états de la matière très variés et avec des applications potentielles. Sr₂IrO₄ est un isolant de Mott exotique car induit par un fort couplage spin-orbite. Il permet d'étudier l'impact des corrélations électroniques sur les propriétés de basses énergies sous un angle nouveau. L'objet de cette thèse est l'étude expérimentale des propriétés électroniques de ces composés iridates par des mesures d'ARPES permettant des observations directes de la structure électronique dans l'espace réciproque et de RMN et μSR, qui donnent une vision locale dans l'espace réel. Nous nous sommes en particulier intéressés à la transition isolant métal pouvant survenir en dopant ce composé. Une façon originale de doper Sr₂IrO₄ que nous avons étudiée en détails est de substituer l'iridium par du rhodium. Les deux sont isovalents, mais le rhodium capture un électron conduisant à un dopage effectif en trous. Grâce à l’ARPES, nous avons mis en évidence les différentes bandes de la structure électronique. Nous avons étudié attentivement le caractère orbital de ces bandes et mis en évidence des anisotropies résiduelles en certains points de l’espace réciproque, survivant malgré la présence du fort couplage spin-orbite. Ceci, ainsi que des effets de repliement de la structure électronique, donnent lieu à des variations brutales d'intensité, qui doivent être prises en compte pour analyser correctement les spectres. Lors du dopage avec le Rh, la phase métallique obtenue reste très incohérente, avec une absence de pic de quasiparticule et un pseudogap uniforme sur l'ensemble de la surface de Fermi. Le gap de Mott ne semble pas se fermer. Le pseudogap peut révéler une brisure de symétrie mais aussi l’effet du désordre introduit par le Rh et nous discuterons son origine, en lien avec la physique d’autres systèmes corrélés. Nous montrons que pour de faibles taux de substitution Ir/Rh, l’ajout de porteurs trous contrôle le comportement du système alors qu’à des taux de substitutions plus élevés, le nombre de porteurs est stable mais le désordre augmente et contrôle à son tour la physique. Nous nous sommes aussi intéressés aux propriétés électroniques et magnétiques sondées par la RMN de l'oxygène 17 sur poudre et poudre orientée et par μSR. La RMN permet de différencier les deux sites d'oxygène de Sr₂IrO₄ nous permettant de déterminer certains paramètres nucléaires préalables à l'étude fine des propriétés électroniques. Dans le composé pur, nous avons étudié la transition magnétique et observé ce qui semble être le développement d'un moment sur l'oxygène apical. Dans les composés dopés, nous ne voyons pas de désordre structural important malgré des taux de dopage allant jusqu'à 15% de rhodium. Les propriétés magnétiques présentent néanmoins des signes d’inhomogénéité, plus marqués dans le cas du dopage lanthane. Les fluctuations dans le composé métallique montrant une prédominance des corrélations antiferromagnétiques. De son côté, la μSR a permis de construire le diagramme de phases de la transition antiferromagnétique et de mettre en évidence l'inhomogénéité de la transition magnétique dans les échantillons faiblement dopés. À basse température, nous confirmons que la phase magnétique évolue, peut-être avec l’apparition d’un moment sur l’oxygène, et cet effet est même renforcé dans les composés faiblement dopés. Au-dessus de la température de transition antiferromagnétique, nous n'avons pas trouvé de signature d'une transition vers une phase de boucles de courant observée par d'autres techniques. Cette étude permet d’attribuer à Sr₂IrO₄ dopé rhodium le caractère assez rare de matériau 2D fortement corrélé à désordre contrôlé. De manière plus générale, cet exemple devrait permettre de mieux comprendre les effets éventuels de désordre associés à d’autre façons de doper les iridates. / The study of the insulating Mott state is a very active field of research in condensed matter because of the strong correlations usually at play which can lead to a large variety of states of matter, with potential applications. Sr₂IrO₄ is an exotic Mott insulator because it is induced by a strong spin-orbit coupling. It allows studying the impact of electronic correlations on the low energy properties from a new viewpoint. The subject of this thesis is the experimental study of the electronic properties of these iridate compounds by ARPES measurements allowing direct observations of the electronic structure in reciprocal space and NMR and μSR, which give a local view in real space. We have in particular studied the metal to insulator transition which can occur in this compound upon doping. An original way to dope Sr₂IrO₄ that we have investigated in details is to substitute iridium by rhodium. Both are isovalent but the rhodium captures an electron leading to an effective hole doping. Thanks to ARPES we have identified the different bands in the electronic structure. We have studied in details the orbital character of these bands and pointed out residual anisotropies at some points in the reciprocal space, which survive despite the strong spin-orbit coupling. This, as well as the folding effects of the electronic structure, give rise to sudden variations in intensity, which must be taken into account in order to correctly analyze the spectra. Upon doping with Rh, the obtained metallic phase remains very incoherent, with no quasiparticle peak and a uniform pseudogap over the full Fermi surface. The Mott gap does not seem to be closing. The pseudogap can reveal symmetry breaking but also the effect of the disorder introduced by the Rh and we will discuss its origin, in relation to the physics of other correlated systems. We show that for low Ir/Rh substitution rates, the addition of hole carriers controls the behavior of the system while at higher substitution rates, the number of carriers is stable but the disorder increases and in turn controls physics.We were also interested in the electronic and magnetic properties probed by 17 oxygen NMR on powder and oriented powder samples and by μSR. NMR makes it possible to differentiate the two oxygen sites in Sr₂IrO₄ allowing determining some nuclear parameters necessary to the fine study of the electronic properties. In the pure compound, we have studied the magnetic transition and observed what appears to be the development of a moment on the apical oxygen. In the doped compounds, we do not see any significant structural disorder despite doping levels up to 15% rhodium. However, the magnetic properties nevertheless show signs of inhomogeneity, which are more pronounced in the case of lanthanum doping. The fluctuations in the correlated metal compound show a predominance of antiferromagnetic correlations. From our μSR investigation, we could construct the magnetic phase diagram which highlights the inhomogeneity of the magnetic transition in the low-doped samples. At low temperature, we confirm that the magnetic phase evolves, perhaps with the appearance of a moment on the oxygen, and this effect is even enhanced in the lightly doped compounds. Above the antiferromagnetic transition temperature, we did not find signatures of the current loop phase observed by other techniques. This study makes it possible to attribute to Sr₂IrO₄ doped with rhodium the rather rare character of strongly correlated 2D material with controlled disorder. More generally, this example should provide a better understanding of the potential effects of disorder associated with other ways to dope iridates.

Les nuages, le lait, le papier, les tissus biologiques appartiennent tous à une même classe de milieux que l'on nomme diffusants de part leur habilité à transformer une onde incidente collimatée en un faisceau diffus. L'imagerie, ou le transfert d'information à travers ces milieux est a priori plus difficile qu'en milieu homogène, et les méthodes actuelles nécessitent une caméra en transmission du milieu complexe considéré. La présence de cette caméra est souvent considérée comme une faille de ces méthodes car la transmission de ces milieux est souvent hors d'atteinte par l'opérateur. Dans cette thèse nous posons la question du lien qui existe entre la lumière réfléchie et la lumière transmise en milieux fortement diffusant. Nous traitons ce problème de manière statistique et nous intéressons à la dépendance statistique qui existe entre la lumière réfléchie et la lumière transmise. Nous verrons que ce lien statistique persiste même pour des milieux fortement diffusants. Ce lien statistique peut être a la base de nouvelles méthodes de contrôle du front d'onde en milieux diffusant n'utilisant que des informations réfléchies par le milieu, permettant l'imagerie, le dépôt d'énergie ou d'informations à travers des milieux fortement diffusants. / Clouds, milk, paper or biological tissues are called scattering media for light. Indeed when a plane wave encounters one a these media, the light is scattered and looses its preferential direction. Consequently, imaging through these media is more difficult than in homogeneous media. The existing methods rely on a CCD camera measuring the transmitted light. Nonetheless, the transmitted side of the sample is most of the time out of reach of the operator. In this thesis we interest ourselves to the link that exists between the reflected light and the transmitted light for thick scattering media. From a statistical point of view, this link is equivalent to the statistical dependency between the reflected light and the transmitted light. We show that the statistical dependency persists even for very thick media allowing us to propose new imaging modalities based on it. This statistical dependency between the reflected and the transmitted light is a very rich function of the parameters of the system, and may allow us to control the transmitted light using reflected information only.

No description available.

We report on calculations of smoothed spectral correlations in the twodimensional Anderson model for weak disorder. As pointed out in (M. Wilkinson, J. Phys. A: Math. Gen. 21, 1173 (1988)), an analysis of the smoothing dependence of the correlation functions provides a sensitive means of establishing consistency with random matrix theory. We use a semiclassical approach to describe these fluctuations and offer a detailed comparison between numerical and analytical calculations for an exhaustive set of two-point correlation functions. We consider parametric correlation functions with an external Aharonov-Bohm flux as a parameter and discuss two cases, namely broken time-reversal invariance and partial breaking of time-reversal invariance. Three types of correlation functions are considered: density-of-states, velocity and matrix element correlation functions. For the values of smoothing parameter close to the mean level spacing the semiclassical expressions and the numerical results agree quite well in the whole range of the magnetic flux.

Title: U in metastable systems: structure, magnetism, and superconductivity Author: Volodymyr Buturlim Department / Institute: Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: This thesis presents studies of U-Nb and U-Ti alloys and hydrides synthesized via different technological paths. Investigation of the microstructure of the alloys with different concentrations of Ti (Nb) allowed to find the optimum setting for stabilization of the metastable bcc U allotrope. Ultra-fast cooling accompanied by alloying leads to retention of materials with high degree of atomic disorder apparent from the studies of their transport properties. The alloys exhibit a weakly paramagnetic ground state and low-temperature superconductivity, the critical temperature of which has only moderate variations with Ti (Nb) concentrations and which has very high upper critical fields. Interaction with hydrogen allows to stabilize two distinctive forms of hydride: β-UH3 and UTi2Hx. β-UH3 alloyed by Ti (Nb) orders ferromagnetically with transition temperatures exceeding 170 K, weakly influenced...

The Standard Model of elementary particles (SM) predicts the existence of a neutral scalar Higgs boson. However, there are also extensions of the SM (such as the MSSM) in which a number of Higgs bosons is predicted. Especially the additional presence of pseudoscalar and charged Higgs bosons represents one of the crucial differences between the SM and its exten- sions. This work develops a method for determination of the spin and parity of the Higgs boson in several H → ττ decays, namely: H→ τ+ τ− → (h+ ντ )(h− ¯ντ ), H→ τ+ τ− → ( + ντ ¯ν )(π− ¯ντ ) and H→ τ+ τ− → ( + ντ ¯ν )( − ¯ντ ν ), where h denotes π or ρ meson. The method is based on the angular and energy correlations of charged final products from the decays mentioned above. Additionally, the work studies the possibility of signal (Higgs boson decay) and background (Z → ττ decay) discrimination, when one considers a decaying boson with spin 1. All calcula- tions are done in the leading order of perturbation theory. 1

Abstract This thesis project is divided in two parts. The first part examines the possibility that correlation matrix estimates based on an outlier sample would contain information about extreme events. According to my findings, such methods do not perform better than simple shrinkage methods where robust shrinkage targets are used. The method tested is especially outperformed when it comes to the extreme events, where a shrinkage of the correlation matrix towards the identity matrix seems to give the best result. The second part is about valuation of skewness in marginal distributions and the penalizing of heavy tails. I argue that it is reasonable to use a degrees of freedom parameter instead of kurtosis and a certain regression parameter, that I develop, instead of skewness due to robustness issues. When minimizing the one period draw-down is our target, the "value" of skewness seems to have a linear relationship with expected returns. Re-valuing of expected returns, in terms of skewness, in the standard Markowitz framework will tend to lower expected shortfall (ES), increase skewness and lower the realized portfolio variance. Penalizing of heavy tails will most times in the same way lower ES, lower kurtosis and realized portfolio variance. The results indicate that the parameters representing higher order moments in some way characterize the assets and also reflect their future behavior. These properties can be used in a simple optimization framework and seem to have a positive impact even on portfolio level

Critical and residual states are key soil conditions relevant to slope stability. Evaluating the available shear strength in relation to these conditions is crucial for reliable stability analyses. The best way to determine the strength parameters is through properly selected laboratory tests of soil mechanics. However, in specific cases, these parameters can be estimated based on other material properties of soils. The work clarifies the applicability of various correlation equations from the literature and proposes new relationships, created from laboratory- determined results of strength and index parameters of soils from the Bohemian Central Mountains. It shows how different equations or different material properties of soils can predict the required value of strength. The work also describes how the residual strength of soils and its estimation can be affected. This is mainly caused by the clay fraction proportion and by the shear rate used in its laboratory determination. The results are applied to a specific geotechnical problem - to estimate the critical state and the residual friction angle of soils from the selected study area of the D8 motorway, which is well known thanks to the stability problems. Last but not least, various errors and misunderstandings are discussed, which are often...

How can fluctuations in one-dimensional time series data be characterized and how can detected effects be decomposed into their dynamical origins or causes? In the context of these questions, a variety of problems are discussed and solutions are introduced. The first issue concerns the causes of anomalous diffusion. A previously proposed framework decomposes the Hurst exponent into the Joseph, Noah, and Moses effects. They represent violations of the three premises of the central limit theorem. Here the framework is applied to an intermittent deterministic system, which exhibits a rich combination of all three effects. Nevertheless, the results provide an intuitive interpretation of the dynamics. In addition, the framework is theoretically discussed and connected to a calculation that proves its validity for a large class of systems. Once the type of anomalous statistical behavior is classified, one might ask what the dynamical origin of the effects is. Especially the property of long range temporal correlations (the Joseph effect) is discussed in detail. In measurements, they might arise from different dynamical origins or can be explained as an emerging phenomenon. A collection of different routes to the observed behavior is established here. A popular tool for detecting long range correlations is detrended fluctuation analysis. Its advantages over traditional methods are stability and smoothness for timescales up to one fourth of the measurement time and the ability to neglect the slow dynamics and trends. Recently, a theory for an analytical understanding of this method was introduced. In this thesis, the method is further analyzed and developed. An approach is presented that enables scientists to use this method for short range correlated data, even if the dynamics is very complex. Fluctuations can be decomposed into a superposition of linear models that explain its features. Therefore, on the one hand, this thesis is about understanding the effects of anomalous diffusion. On the other hand, it is about widening the applicability of one of its detection methods such that it becomes useful for understanding normal or complex statistical behavior. A good example of a complex system, where the proposed stochastic methods are useful, is the atmosphere. Here it is shown how detrended fluctuation analysis can be used to uncover oscillatory modes and determine their periods. One of them is the El Ni\~no southern oscillation. A less well known and more challenging application is a 7--8 year mode in European temperature fluctuations. A power grid is a very different type of complex system. However, using the new method, it is possible to generate a data model that incorporates the important features of the grid frequency.

Lors du présent travail, des 4-nitrobenzochalcogénadiazoles ont été synthétisés et une étude cinétique approfondie de leur réactivité vis-à-vis diverses entités nucléophiles a été réalisée. Cette étude a permis la détermination des paramètres d’électrophile E de ces espèces et leur insertion dans l’échelle universelle d’électrophilie de Mayr. En outre, sur la base des diverses corrélations Structure-Réactivité étudiées, les mécanismes d’interaction entre les 4-nitrobenzochalcogénadiazoles et les nulcéophiles utilisés ont été élucidés et un mécanisme de transfert d’électrons (SET) a été suggéré pour la complexation du 4-nitrobenzofurazane par les anions de phénate en raison de l’obtention d’une valeur très élevée de βnuc (βnuc = 1,12). En vue d’activer les propriétés électrophiles de nos 4-nitrobenzochalcogénadiazoles, nous avons procédé à la quaternarisation de leurs motifs annélés. De nouveaux électrophiles positivement chargés ont été ainsi obtenus, et une étude cinétique approfondie de leur réactivité électophile vis-à-vis des anilines, des amines et des indoles, nous a permis de mettre l’accent sur la réactivité électrophile ambidente de ces espèces. D’une manière surprenante, l’interaction entre le 4-nitrobenfurazane et le 4-nitrobenzothiadiazole N-méthylés avec une série d’anilines para-Y-substituées a permis de définir des corrélations de Mayr, Hammett et Brönsted non linéaires. Cette déviation des divers graphes obtenus a été expliquée par le changement du mécanisme réactionnel. D’autre part, l’étude de la réactivité du 4-nitrobenzosélénadiazole N-méthylé vis-à-vis une série d’amines s’est révélée beaucoup plus originale que prévu en raison de la mise en évidence d’une corrélation linéaire de pente unité entre le log(kexp) et le log(kcal). / In the present work, 4-nitrobenzochalcogenadiazols have been synthesized and kinetics for σ-complexation of these compounds with various nucleophiles have been measured in aqueous solutions at 20 °C. According Mayr’s approach, E parameters of 4-nitrobenzochalcogenadiazols have been evaluated and using these values, a positioning of the reactivity of our electrophiles on the electrophilicity scale was possible. Based on Structure-Reactivity correlations, possible mechanistic pathways for each process were given and the abnormally high Brönsted coefficient βnuc of 1.12 reveals that the σ-complexation reaction of 4-nitrobenzofurazan with a series of 4-X-substituted phenoxide ions may proceed via single electron transfer process (SET).In order to increase the electrophilicity parameters of 4-nitrobenzochalcogenadiazols, we proceeded to the N-méthylation of their annelated rings.Thus, a new serie of positively charged electrophiles has been obtained. kinetic study of the coupling of N-methylated compounds with para-substituted anilines, indoles and amines showed that these salts can react as ambident electrophiles. Surprisingly, kinetics of coupling of N-méthylaed 4-nitrobenzofurazan and 4-nitrobenzothiadiazol with 4-Y-substituted anilines, resulted in a non linear Mayr type plot. Hammet and Brönsted plots were also non linear. These results have been interpreted as reflecting changes in the mechanistic process. Interestingly, when studying the reactivity of N-methylated benzoselenadiazol versus a series of amines, a satisfactory correlation between the log values of experimental and calculated rate constants with a slope very close to unity has been obtained and discussed.