No abstract provided. / Thesis / Doctor of Philosophy (PhD) / Scope and contents: The atomic vibrations in rubidium have been studied by the method of slow neutron spectrometry. The results have been analysed to yield atomic force constants which are used to compute the phonon frequency distribution. An interesting effect in the [00ζ]L branch has been examined, and an explanation of the observations is offered. Anharmonic calculations of frequency shifts and widths are presented, as well as a calculation of the anharmonic heat capacity. The third and fourth derivatives of the real space interatomic potential, which are required for these computations, are estimated in various ways. A determination of the lattice spacing of rubidium by neutron diffraction is described.

The phenomenon of pairing in atomic and nuclear many-body systems gives rise to a great number of different physical properties of matter, from areas as seemingly diverse as the shape of stable nuclei to superconductivity in metals and superfluidity in neutron stars. With the experimental realisation of the long sought BCS-BEC crossover observed in trapped atomic gases - where it is possible to fine tune the s-wave scattering length a of a many-fermion system between a dilute, correlated BCS-like superfluid of Cooper pairs and a densely packed BEC of composite bosons - pairing problems in atomic physics have found renewed interest in recent years. Given the high precision techniques involved in producing these trapped gas condensates, we would like to employ a suitably accurate many-body method to study such systems, preferably one which goes beyond the simple mean-field picture.The Coupled Cluster Method (CCM) is a widely applied and highly successful ab initio method in the realm of quantum many-body physics and quantum chemistry, known to be capable of producing extremely accurate results for a wide variety of different many-body systems. It has not found many applications in pairing problems however, at least not in a general sense. Our aim, therefore, is to study various models of pairing using a variety of CCM techniques - we are interested in studying the generic features of pairing problems and in particular, we are especially interested in probing the collective modes of a system which exhibits the BCS-BEC crossover, in either the BCS or BEC limit. The CCM seems a rather good candidate for the job, given the high precision results it can produce.

In this thesis, the main perturbation problems encountered in quantum mechanics have been studied.Since the special functions and orthogonal polynomials appear very extensively in such problems, we emphasize on those topics as well. In this context, the classical quantum mechanical anharmonic oscillators described mathematically by the one-dimensional Schr&uml / odinger equation have been treated perturbatively in both finite and infinite intervals, corresponding to confined and non-confined systems, respectively.

Enormous advances in computing power in recent decades have made it possible to perform accurate numerical simulations of a wide range of systems in condensed matter physics. At the forefront of this progress has been density functional theory (DFT), a very popular approach to tackling the complexity of quantum-mechanical systems that very often strikes a good balance between accuracy and tractability in light of the finite computational resources available to researchers. This thesis describes work utilising DFT methods to tackle two distinct problems. Firstly, the theoretical prediction of stable and metastable periodic structures under specified conditions using the ab initio random structure searching (AIRSS) method, which involves a large scale exploration of the Born-Oppenheimer energy surface, and secondly the use of a vibrational self-consistent field (VSCF) approach to investigate the effects of nuclear motion and anharmonicity in crystal systems, which involves a local exploration of the Born-Oppenheimer energy surface. The AIRSS crystal structure prediction method is here applied to a study of defect structures in graphene. It is also applied to a study of the xenon-oxygen binary system under a range of geological pressures (83–200 GPa). Novel xenon oxide structures are predicted and characterised theoretically. This work was carried out in collaboration with an experimental study of the system at the lower end of the pressure range. The VSCF approach to investigating anharmonicity is here applied to the study of tin selenide (SnSe), a material that has recently been shown to demonstrate consider- able promise as a thermoelectric material. In this thesis, the effects of the anharmonic nuclear motion on the vibrational and electronic properties of SnSe are investigated quantitatively.

Title: Theory and application of optical spectroscopic methods for structural molecular studies Author: RNDr. Jana Hudecová Department / Institute: Institute of Organic Chemistry and Biochemistry Supervisor of the doctoral thesis: Prof. RNDr. Petr Bouř, DSc. Abstract: In the thesis, methods of the chiroptical spectroscopy (Raman optical activity, electronic and vibrational circular dichroism, circularly polarized luminescence) were utilized to obtain information on structure of chiral molecules. In four main projects, we focused on improving accuracy of quantum-chemical computations used for interpretation of experimental spectra by including anharmonic effects, solvent, molecular flexibility and dynamics. In the first project, the normal mode geometry optimization method was investigated and a suitable frequency limit providing realistic vibrational band broadening was found. Then the ability of harmonic and anharmonic computational approaches to describe the C-H stretching vibrations was explored for three terpene molecules and four spectroscopic methods. In the third project, we estimated the role of dispersion forces and different organic solvents for conformer equilibria and dynamics of cyclic dipeptides containing tryptophan. In the last project, circularly polarized luminiscence spectra, which were...

Terahertz (THz) spectroscopy is a powerful tool that uses ultrashort pulses of light to study the properties of materials on picosecond time scales. THz light can be generated through a variety of methods. In our lab, we generate THz through the process of optical rectification in nonlinear optical (NLO) organic crystals. THz light can be used to study several phenomena in materials, such as spin precession, electron acceleration, vibrational and rotational motion. The work presented in this dissertation is divided into two parts: (1) the generation of THz light and (2) applications of THz light. The first portion of this work shows how THz light is generated, with an emphasis on the generation through optical rectification. We also show how to improve the generation of THz light by creating heterogenous multi-layer structures with yellow organic THz generation crystals. Additionally, we show that crystals used for THz generation can also be used to generate second-harmonic light. In the second half of this work, we show that THz light can be used to study the vibrational motion of molecular systems. We model how resonant vibrational modes in a fluorobenzene molecule can be excited with a multi-THz pump to transfer energy anharmonically to non-resonant modes. We also show that we can use two-dimensional (2D) THz spectroscopy to excite infrared-active vibrational modes and probe Raman-active modes in a CdWO4 crystal to obtain a nonlinear response. We show that the nonlinear response is due to anharmonic coupling between vibrational modes and we can quantify the relative strengths of these anharmonic couplings, which previously was only accessible through first-principles calculations.

Doctor of Philosophy / Department of Physics / Itzhak Ben-Itzhak / Patrick Richard / This work focuses on the ultrafast dynamics of electrons and phonons in graphitic materials. In particular, we experimentally investigated the factors which influence the transport properties of graphite and carbon nanotubes. In the first part of this dissertation, we used Time-resolved Two Photon photoemission (TR-TPP) spectroscopy to probe the dynamics of optically excited charge carriers above the Fermi energy of double-wall carbon nanotubes (DWNTs). In the second part of this study, time-resolved anti-Stokes Raman (ASR) spectroscopy is applied to investigating in real time the phonon-phonon interactions, and addressing the way the temperature affects the dynamics of single-wall carbon nanotubes (SWNTs) and graphite. With respect to the first part, we aim to deeply understand the dynamics of the charge carriers and electron-phonon interactions, in order to achieve an as complete as possible knowledge of DWNTs. We measured the energy transfer rate from the electronic system to the lattice, and we observed a strong non-linear increase with the temperature of the electrons. In addition, we determined the electron-phonon coupling parameter, and the mean-free path of the electrons. The TR-TPP technique enables us to measure the above quantities without any electrical contacts, with the advantage of reducing the errors introduced by the metallic electrodes. The second investigation uses time-resolved ASR spectroscopy to probe in real time the G-mode non-equilibrium phonon dynamics and the energy relaxation paths towards the lattice by variation of the temperature in SWNTs and graphite. The lifetime range of the optically excited phonons obtained is 1.23 ps to 0.70 ps in the lowest (cryogenic temperatures) and highest temperature limits, respectively. We have also observed an increase in the energy of the G-mode optical phonons in graphite with the transient temperature. The findings of this study are important since the non-equilibrium phonon population has been invoked to explain the negative differential conductance and current saturation in high biased transport phenomena.

L'instabilité du spectre des opérateurs non-autoadjoints constitue la thématique centrale de cette thèse. Notre premier objectif est de mettre en évidence ce phénomène dans le cas de certains modèles naturels tels que l'opérateur d'Airy, l'oscillateur harmonique ou l'oscillateur cubique complexes. Dans ce but, nous nous intéressons au comportement des projecteurs spectraux associés aux valeurs propres de ces opérateurs, poursuivant une démarche initiée par E. B. Davies. Le second objectif de notre travail consiste à montrer de quelle manière ces modèles peuvent contribuer à la compréhension de certains problèmes issus de domaines mathématiques et physiques aussi variés que la mécanique quantique, la supraconductivité ou la théorie du contrôle. Nos résultats sur l'instabilité spectrale de l'oscillateur cubique complexe viennent ainsi corroborer un travail de B. Krejcirik et P. Siegl, soulignant l'impossibilité de fournir une justification rigoureuse aux théories actuelles de la mécanique quantique non-hermitienne. Par ailleurs, nous nous appuyons sur les propriétés des modèles mentionnés ci-dessus pour obtenir des résultats sur le spectre et la résolvante d'opérateurs de Schrödinger à potentiels imaginaires purs dans des ouverts bornés. Ces résultats peuvent en particulier être appliqués à l'étude du système de Ginzburg-Landau dépendant du temps en supraconductivité. Enfin, nous présentons des résultats sur la contrôlabilité d'équations paraboliques dégénérées qui reposent sur une étude spectrale et pseudospectrale de l'opérateur d'Airy et de l'oscillateur harmonique complexes. Ce dernier travail est le fruit d'une collaboration avec K. Beauchard, B. Helffer et L. Robbiano. / Spectral instability of non-selfadjoint operators is the main subject of this thesis. Our first goal is to understand the pseudospectral behavior of natural models such as the complex Airy operator, harmonic oscillator and cubic oscillator. To this purpose, we analyze the asymptotic behavior of the spectral projections associated with the eigenvalues of these operators, following a work initiated by E.B. Davies. Our second goal is to illustrate how such models can be used in several problems arising in quantum mechanics, superconductivity or control theory. For instance, our results on the spectral instability of the complex cubic oscillator enable us to confirm that the current theory of non-hermitian quantum mechanics can not be rigorously justified, as recently pointed out by B. Krejcirik and P. Siegl. On the other hand, we obtain spectral information and resolvent estimates for semi-classical Schrödinger operators with purely imaginary potentials in a bounded domain, by using the properties of the models mentioned above. In particuler, these results entail some information on the time-dependent Ginzburg-Landau system in superconductivity. Finally, we reproduce a joint work with K. Beauchard, B. Helffer et L. Robbiano in which the controllability of some degenerate parabolic operators is investigated. An analysis of the spectrum and resolvent of the complex Airy operator and harmonic oscillator yields some controllability and non-controllability results for the equation under consideration.

In dieser Arbeit werden Massen und Zerfallskonstanten von pseudoskalaren Mesonen, insbes. dem Pion und dem D-s-Meson, im Rahmen der Quantenchromodynamik (QCD) berechnet. Diese Größen wurden im Rahmen der Gitter-QCD, einer gitter-regularisierten Form der QCD, mit vier dynamischen Twisted-Mass Fermionen (Up-, Down-, Strange- und Charm-Quark) berechnet. Dieses Setup bieten den Vorteil der automatischen O(a)-Verbesserung. Der Gitterabstand a wurde mit Hilfe der Pion-Masse und -Zerfallskonstante durch Extrapolation zum physikalischen Punkt, geg. durch das physikal. Verhältnis von f_pi/M_pi, bestimmt. Dabei kamen Formeln aus der chiralen Störungstheorie, die die speziellen Diskretisierungseffekte des Twisted-Mass-Formalismus berücksichtigen, zum Einsatz. Die bestimmten Werte des Gitterabstands, a=0.0899(13) fm (@ beta=1.9), a=0.0812(11) fm (@ beta=1.95) und a = 0.0624(7) fm (@beta=2.1) liegen etwa fünf Prozent über denen vorheriger Bestimmungen (Baron et. al. 2010). Dies erklärt sich vor allem durch eine Untersuchung bezüglich der Anwendbarkeit des Bereiches der Up-/Down-Quark-Massen auf die verwendeten Extrapolationsformeln. Zur Untersuchung des physikalischen Grenzwertes von f_{D_s} werden Formeln der chiralen Störungstheorie für schwere Mesonen (HM-ChiPT) eingesetzt. Das Endergebnis dieser Betrachtung f_{D_s} = 248.9(5.3) MeV liegt etwas über vorherigen Bestimmungen (ETMC 2009, arXiv:0904.095. HPQCD 2010, arXiv:1008.4018) und etwa zwei Standardabweichungen unter dem Mittel aus experimentellen Werten (PDG 2012). Ein weiterer Teil dieser Arbeit behandelt die i.A. schwierige Berechnung von unverbundenen Beiträgen, die z.B. bei der Berechnung der Masse des neutralen Pions eine Rolle spielen. In dieser Arbeit wird eine neue Methode zur Approximation solcher Beiträge vorgestellt, welche auf der sog. Quasi-Monte-Carlo-Methode (QMC-Methode) beruht. Diese Methode birgt große Möglichkeiten zu enormen Einsparungen der Rechenzeit. / This work deals with the determination of decay constants and masses of the pion and D-s meson. This happens in the framework of lattice QCD, a lattice regularised form of QCD. The four dynamical fermions (up, down, strange and charm quark) are described by the twisted-mass approach (TM-QCD) featuring automatic O(a) improvement. The lattice spacing a has been determined using the pion mass and decay constant extrapolated to the physical point, which is determined by the physical ratio f_pi/m_pi. In order to obtain an accurate description, new formulae from Chi-PT, taking into account the special form of discretisation effects of TM-QCD have been employed. The determined results of a = 0.0899(13) fm (@ beta=1.9), a = 0.0812(11)fm (@ beta=1.95) and a = 0.0624(7) fm (@ beta=2.1) are approximately 5% larger than previous determinations (Baron et. al. 2010). This shift is most likely explained by the reduced range of pion masses (

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