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When a liquid is cooled below its equilibrium freezing temperature, it becomes supercooled and the molecular motions slow down until the system becomes kinetically arrested, forming a glass, at the glass transition temperature. These amorphous materials have the mechanical properties of a solid while retaining the structural properties of a liquid, but do not exhibit the usual features of a thermodynamic phase transition. As such, they present a number of important challenges to our understanding of the dynamics and thermodynamics of condensed phases. For example, supercooled liquids are classified on the basis of the temperature dependence of their transport properties and structural relaxations times. Strong liquids display an Arrhenius behavior, with the logarithm of their viscosity growing linearly with inverse temperature. Fragile liquids behave in a super-Arrhenius manner, where the viscosity appears to diverge at temperatures above absolute zero, suggesting the possibility of an underlying thermodynamic origin to the glass transition. Some complex, network forming liquids, such as water and silica have also been shown to have a dynamical crossover from fragile to strong liquid behavior as the temperature is decreased. The potential energy landscape paradigm, combined with inherent structure formalism, provide a framework for connecting the way particles pack together with the thermodynamics and dynamics of the liquid and glassy phases. However, the complexity of this multi-dimensional surface makes it difficult to fully characterize and rigorous relationships between the nature of particle packing and glass forming properties have not been established. The goal of this thesis is to study some of the general features of glass transition and find the connection between the dynamics and the thermodynamics of glass forming liquids. To this end, the packing landscapes of quasi-one-dimensional hard discs and hard spheres are studied. A two dimensional system of hard discs with diameter σ, confined between two hard walls (lines) of length L, separated by a distance 1<Hd/σ< 1+√(3/4), is studied by using the Transfer Matrix (TM) method and Molecular Dynamics (MD) simulations. The complete packing landscape is characterized in terms of the density distribution of inherent structures and the number of local defect states. It is shown that this model exhibits a dynamic fragile-strong liquid crossover at the maximum in the constant pressure heat capacity (Cp) for the system, similar to that observed in anomalous network forming liquids such as water and silica. Furthermore, we find that rescaling the relaxation times of systems with different channel widths by the relaxation time at the Cp maximum causes all the data to collapse on a single master curve. The Cp maximum occurs at a critical value of the defect concentration. At high defect concentrations, where the defects interact, the fluid is fragile. When the defect concentration is low, relaxation appears to occur through the hopping of isolated defects, leading to Arrhenius dynamics. This suggests the thermodynamics associated with the Cp maximum is intimately related to the dynamic crossover. A system of three-dimensional hard spheres confined in a narrow channel was used to study the effect of a more complicated landscape on the dynamics of the system. For this system, the thermodynamic and dynamic properties of the system were studied for two different channel diameters, the 1<Hd/σ<1+√(3/4) case, which only allows first neighbors contact for the spheres and, 1+√(3/4)< Hd/σ < 1.98, which allows second neighbors contact to exist. For the first case, the TM method was implemented to obtain the thermodynamic properties and MD simulation was used to measure the dynamics. For the case that the second neighbor contact is allowed 1+√(3/4)< Hd/σ < 1.98. The thermodynamic and dynamic properties were obtained using MD simulations. In this channel diameter range, the system creates chiral helical jammed packings and defect states appear where sections of helices with different local chiralities come into contact. The equation of state (EOS) shows the presence of two heat capacity maxima. The high density Cp maximum is linked to fragile strong crossover. Finite size scaling analysis shows that the low density Cp maximum is related to an orientational order transition stabilized by the presence of the defects. This type of transition has been shown to exist in bulk two-dimensional systems but this work is the first study that provides strong evidence of the existence of this transition in a quasi-one-dimensional system in a system with short-range interactions.

A searched for narrow-band-noise (NBN) modulations of the infrared transmission in blue bronze has been performed. No modulations were observed, giving an upper limits for NBN changes in the absorption coefficient of )2000/(/3.0.andlt;.cmNBN. The implication of these results on proposed CDW properties and NBN mechanisms are discussed. An infrared microscope with a capability of doing both reflectance and transmission measurements has been integrated into the previous electro-transmission system with tunable diode lasers. Electro-optic experiments were done using the microscope for the studies of the CDW states of K0.3MoO3 (blue bronze) and orthorhombic TaS3. The electro-reflectance signal for blue bronze has been evidenced for the first time. The infrared reflectance of K0.3MoO3 varied with position when a voltage greater than the CDW depinning threshold is applied. The spatial dependence of .R/R was slightly different than for ./, in that the magnitude of .R/R decreased and, for low voltages and frequencies, the signal became inverted near the contacts. Perhaps the differences might be associated with changes in the CDW properties on the surface. For blue bronze, the electro-reflectance signal was measured to be smaller than electro-transmittance signal by one order of magnitude for light polarized transverse to the chain direction, while the electro-reflectance signal for parallel polarized light was found to be a few times smaller than for transverse polarized light. The fits of the electro-reflectance spectrum showed that the changes in background dielectric constant were ~ 0.05 % and/or oscillator strength and/or frequency shifts of the phonons were ~ 0.05 % and ~ 0.005 cm-1 in the applied electric field. We also found that parallel polarized phonons are affected by CDW strain, and these changes dominate the electro-reflectance spectrum. We have examined the electro-reflectance spectra associated with CDW current investigation for light polarized parallel to the conducting chains for signs of expected current-induced intragap states, and conclude that the density of any such states is at most a few times less than expected. We have observed a large (~1%) change in infrared reflectance of orthorhombic TaS3, when its CDW is depinned. The change is concentrated near one current contact. Assuming that the change in reflectance is proportional to the degree of CDW polarization, we have studied the dynamics of CDW repolarization through position dependent measurements of the variation of the electro-reflectance with the frequency of square wave voltages applied to the sample, and have found that the response could be characterized as a damped harmonic oscillator with a distribution of relaxation (i.e. damping) times. The average relaxation time, which increases away from the contacts, varies with applied voltage as with p ~ 3/2, but the distribution of times broadens as the voltage approaches the depinning threshold. Very low resonant frequencies (~ 1 kHz) indicate a surprisingly large amount of inertia, which is observable in the time dependence of the change in reflectance as a polarity dependent delay of ~ 100 s.

Estudamos as propriedades eletrônicas de dois sistemas quase-unidimensionais distintos, resolvendo autoconsistentemente as equações de Schrödinger e Poisson.O método usado para calcular a estrutura eletrônica deste sistema e baseada na solução da equação de Schrödinger dependente do tempo usando a técnica do Split-Operator. No primeiro sistema estudamos os efeitos da corrugação periódica da interface da estrutura n-AlxGa1-xAs/GaAs na densidade eletrônica ao longo desta interface. A forma geométrica desta interface e do tipo dente de serra. Nas camadas de inversão convencionais, os elétrons estão distribuídos uniformemente ao longo da interface plana da heteroestrutura, mas devido à forma dente de serra desta estrutura, os elétrons se distribuem de maneira não uniforme ao longo da interface, produzindo um gás de elétrons quase-unidimensional. A estrutura que investigamos possui um período de 806 ANGSTROM e uma densidade residual uniforme de impurezas aceitadoras da ordem de 1015 cm-3. Calculamos a estrutura eletrônica do gás de elétrons unidimensional confinado na interface corrugada em função da voltagem aplicada ao gate, da densidade de impurezas doadoras e da temperatura. Os resultados obtidos para a densidade eletrônica mostram que, dependendo da densidade de impurezas doadoras, haverá formação de u gás de elétrons quase-unidimensional nos vértices da estrutura dente de serra. O segundo sistema que estudamos é constituído por um gás de elétrons bidimensional, formado na interface de uma camada de Al1-xGa1-xAs com uma camada de GaAs, sobre a qual, temos uma estrutura periódica de \"gates\". Aplicando-se uma voltagem negativa sobre os \"gates\" teremos a formação de fios quânticos nas regiões entre os \"gates\". Neste sistema observamos a transição de um sistema quase-bidimensional para um quase-unidimensional. Investigamos suas propriedades eletrônicas em funçãoo da temperatura, da voltagem aplicada aos \"gates\" e da densidade de impurezas doadoras. / We have studied the electronic properties of two different quasi-one-dimensional systems solving self-consistently the Schrödinger and Poisson equation. The method we use to calculate the electronic levels is based on the solution of the time-dependent Schrödinger equation using the split-operator technique. In the first system we have studied, we present a theoretical calculation of the electronic structure of v-groove quantum wires confined in modulation-doped n-AlxGa1-xAs/GaAs. The system investigated is saw tooth corrugated by bendings with period of 850 ANGSTROM. Results of the electronic structure are obtained as a function of the gate voltage and the donor impurity density. The electronic density shows the existence of a quasi one-dimensional electron gas. The second system studied here is composed by a two-dimensional electron gas confined at the interface of an Al1-xGa1-xAs/GaAs heterostructure, on top of which there is a periodic structure of gates. When a negative voltage is applied to the gates, the regions at the interface beneath them are depleted and quantum wires are formed. We have calculated the electronic structure of subband of that system. We investigated the electronic properties of the quantum wires as a function of gate voltage, from which we determine the threshold between the 2D and ID transitions, the temperature and the ionized donor density.

This thesis presents theoretical investigations of triplet superfluidity (triplet superconductivity) in quasi-one-dimensional organic conductors and ultra-cold Fermi gases. Triplet superfluidity is different from its s-wave singlet counterpart since the order parameter is a complex vector and the interaction between fermions is in general anisotropic. Because of these distinctions, triplet superfluids have different physical properties in comparison to the s-wave case. The author discusses in this thesis the interplay between triplet superconductivity and spin density waves in quasi-one-dimensional organic conductors, and proposes a coexistence region of the two orders. Within the coexistence region, the interaction between the two order parameters acquires a vector structure, and induces an anomalous magnetic field effect. Furthermore, the author analyzes the matter-wave interference between two p-wave Fermi condensates, and proposes a polarization effect. For a single harmonically trapped p-wave Fermi condensate, the author also shows that the expansion upon release from the trap can be anisotropic, which reflects the anisotropy of the p-wave interaction.

Estudamos as propriedades eletrônicas de dois sistemas quase-unidimensionais distintos, resolvendo autoconsistentemente as equações de Schrödinger e Poisson.O método usado para calcular a estrutura eletrônica deste sistema e baseada na solução da equação de Schrödinger dependente do tempo usando a técnica do Split-Operator. No primeiro sistema estudamos os efeitos da corrugação periódica da interface da estrutura n-AlxGa1-xAs/GaAs na densidade eletrônica ao longo desta interface. A forma geométrica desta interface e do tipo dente de serra. Nas camadas de inversão convencionais, os elétrons estão distribuídos uniformemente ao longo da interface plana da heteroestrutura, mas devido à forma dente de serra desta estrutura, os elétrons se distribuem de maneira não uniforme ao longo da interface, produzindo um gás de elétrons quase-unidimensional. A estrutura que investigamos possui um período de 806 ANGSTROM e uma densidade residual uniforme de impurezas aceitadoras da ordem de 1015 cm-3. Calculamos a estrutura eletrônica do gás de elétrons unidimensional confinado na interface corrugada em função da voltagem aplicada ao gate, da densidade de impurezas doadoras e da temperatura. Os resultados obtidos para a densidade eletrônica mostram que, dependendo da densidade de impurezas doadoras, haverá formação de u gás de elétrons quase-unidimensional nos vértices da estrutura dente de serra. O segundo sistema que estudamos é constituído por um gás de elétrons bidimensional, formado na interface de uma camada de Al1-xGa1-xAs com uma camada de GaAs, sobre a qual, temos uma estrutura periódica de \"gates\". Aplicando-se uma voltagem negativa sobre os \"gates\" teremos a formação de fios quânticos nas regiões entre os \"gates\". Neste sistema observamos a transição de um sistema quase-bidimensional para um quase-unidimensional. Investigamos suas propriedades eletrônicas em funçãoo da temperatura, da voltagem aplicada aos \"gates\" e da densidade de impurezas doadoras. / We have studied the electronic properties of two different quasi-one-dimensional systems solving self-consistently the Schrödinger and Poisson equation. The method we use to calculate the electronic levels is based on the solution of the time-dependent Schrödinger equation using the split-operator technique. In the first system we have studied, we present a theoretical calculation of the electronic structure of v-groove quantum wires confined in modulation-doped n-AlxGa1-xAs/GaAs. The system investigated is saw tooth corrugated by bendings with period of 850 ANGSTROM. Results of the electronic structure are obtained as a function of the gate voltage and the donor impurity density. The electronic density shows the existence of a quasi one-dimensional electron gas. The second system studied here is composed by a two-dimensional electron gas confined at the interface of an Al1-xGa1-xAs/GaAs heterostructure, on top of which there is a periodic structure of gates. When a negative voltage is applied to the gates, the regions at the interface beneath them are depleted and quantum wires are formed. We have calculated the electronic structure of subband of that system. We investigated the electronic properties of the quantum wires as a function of gate voltage, from which we determine the threshold between the 2D and ID transitions, the temperature and the ionized donor density.

This thesis describes the neutron scattering measurements of magnetic excitations in spin-chains and ladders. The first part discusses an experimental investigation of the copper oxide family Sr₁₄Cu₂₄O₄₁ composed of edge-sharing chains and spin-ladders. The study of La₄Sr₁₀Cu₂₄O₄₁ comprises a slightly hole-doped chain and an undoped ladder structure where the chain can be modeled by a ferromagnetic nearest and an antiferromagnetic next-nearest neighbor coupling. The hole effects are apparent in gaps in the dispersion relation and can be described by a charge-density wave agreeing with the commensuration of the dispersion. Investigating the undoped ladder establishes the exchange constants including a cyclic exchange manifested by the two-magnon continuum and the suppression of the S = 1 bound mode. An orbital consideration provides an explanation for the exchanges including the different sizes of rung and leg coupling. The excitation spectrum of the doped ladder in Ca₂.₅Sr₁₁.₅Cu₂₄O₄₁ can be described by a direct comparison with the undoped ladder and the differences consisting of a higher energy mode and subgap scattering can be successfully modeled by the charge spectrum of the ladder calculated from the free electron model. The second part of the thesis investigates the alternating chain material Cu(NO₃)₂ · 2.5D2O and establishes the gapped one-magnon dispersion, the two-magnon continuum and for the first time the S =1 bound mode. Applying magnetic field drives the system through two critical field transitions, condensation of magnons into the ground state and saturation. The modes beyond saturation can be modeled by spin wave theory and the excitations at the first critical field follow Luttinger Liquid behavior. Additionally investigated are the temperature effects with the excitations being of a different nature but containing the signature of a strong correlated system. For an outlook the measurements including temperature and field are provided with further theoretical descriptions necessary.

We studied the structural instabilities of one-dimensional (1D) and quasi-one-dimensional (Q1D) electron-phonon systems at low temperature through two models, SuSchrieffer-Heeger (SSH) and molecular crystal (CM) with and without spin. The phase diagrams are obtained using a Kadanoff-Wilson renormalization group approach (GR). For the 1D half-filled system the study of the frequency dependence of the electronic gap allowed us to connect continuously the two limits, adiabatic and non-adiabatic. The Peierls and Cooper channels interference and the quantum fluctuations reduce the gap. A regime change occurs when the frequency becomes of the order of mean field gap, marking a quantum-classical crossover that is the Kosterlitz-Thouless type. At this level, the effective coupling behaves in power law function on frequency. For the case with spin, a gapped Peierls state is maintained in the non-adiabatic limit, while for the case without spin, the system transits to ungapped disordered state, namely the Luttinger liquid stat (LL). For the SSH model without spin, the GR confirms the existence of a threshold phonon coupling beyond which the gap is restored. The study of the rigidities of the two models without spin allowed us to trace the main features of the LL state predicted by the bosonization method. The study of the Holstein-Hubbard model has allowed us not only to reproduce the phase diagrams already obtained by the Monte Carlo method, but to highlight two additional phases, namely, free fermions phase and the bond charge-density-wave phase. We have extended this study to the quarter-filled Q1D Peierls systems at finite temperature. Within the SSH model, an unconventional superconducting phase with spin singlet symmetry SS-s emerges at low temperature when the deviation to the perfect nesting of the Fermi surface is strong enough. Peierls-SS transition is characterized by the presence of a quantum critical point at low frequency and by a power law behavior of the transition temperature as a function of frequency with an exponent identical to one of 1D system. This exponent which universality has been verified contrasts with the BCS result. Coulomb interactions have been introduced through the study of the extended SSH-Hubbard model. The extension of this work to half-filled SSH and CM cases was also performed.

Nous avons étudiés des fils quantiques dopés de semi-conducteurs gravés par spectroscopie de diffusion Raman. Nous avons observés les excitations du gaz d'électrons. Celles-ci présentent des règles de sélection différentes de celles établies pour les systèmes bi-dimensionnels. Nous avons montré théoriquement qu'elles proviennent de la modification de la structure du champ électromagnétique local provoquée par la géométrie particulière des fils gravés. Pour cela nous avons dû calculer le champ local et l'introduire dans la section efficace de diffusion Raman pour en déduire les règles de sélection de toutes les excitations. Cela a permis de déterminer sans équivoque la nature des excitations qui sont des plasmons. Aucune excitations à une particule ni fluctuations de densité de spin n'a été observées. Nous avons étudié l'évolution continue des dispersions de ces plasmons lorsque la largeur du fil est réduite de 1 micromètre à 30 nm. Jusqu'à 60 nm, celles-ci sont en très bon accord avec les résultats d'un modèle hydrodynamique. Au dessous de 60 nm, la comparaison avec un modèle RPA s'impose. Le plasmon intra-bande dispersif est observé jusqu'à 45 nm, largeur en dessous de laquelle les spectres Raman sont dominés par des excitations localisées qui nécessitent une analyse ultérieure pour en déterminer clairement leur nature. Nous montrons à l'aide du modèle RPA que nous avons atteint la limite quantique pour un fil de largeur 55 nm. Une gamme étroite de fils dont les largeurs sont comprises entre 55 nm à 45 nm permet donc l'étude de gaz strictement unidimensionnel.<br />Nous avons cherché à déterminer la contribution de la forte illumination dans les conclusions précédentes. Nous avons utilisé pour cela la spectroscopie de magnéto-transmission infra-rouge qui ne modifie pas les conditions d'équilibre du gaz d'électrons. Une largeur critique de 130 nm a été extraite, en dessous de laquelle nous n'avons plus aucun signe de la présence d'électrons libres. La comparaison des mesures Raman et infra-rouge a permis l'établissement et la validation d'un modèle microscopique du potentiel de confinement présent dans les fils. Enfin nous avons fabriqués des échantillons de géométries plus complexes. L'observation et l'analyse par diffusion Raman des plasmons dans ces fils a montré que nous pouvions contrôler la géométrie du potentiel confinant les électrons et a mis en évidence des effets nouveaux tels que le repliement et le confinement de plasmons unidimensionnels.

Nous avons étudié les propriétés de transport des ondes de densité de charge dans le composé quasi-unidimensionnel NbSe3, à l'échelle micronique et submicronique (jusqu'à 300nm). Nous avons mis au point un process de salle blanche pour la réalisation de microstructures à onde de densité de charge, connectées électriquement par des contacts ohmiques. Cela nous permit de réaliser des expériences sur l'effet d'une force perpendiculaire au mouvement d'une onde de densité de charge et d'observer que la réduction du champ seuil de dépiégeage mesuré précédemment par un autre groupe était liée à des inhomogénéités d'injection de courant et non à une augmentation de l'effet de taille géométrique et de la gravure sur les propriétés des échantillons comme le champ seuil ou la température de transition. De plus, nous avons effectué des mesures couplées transport/rayons X à haute résolution à l'ESRF (European Synchrotron Radiation Facility). Nous avons observé un accroissement de la cohérence spatiale du condensat quand la cohérence temporelle augmente et nous avons étudié différents mécanismes d'interaction entre deux ondes de densité de charge.