This work is about the properties of several low dimensional, small systems of interacting particles. We demonstrate that interaction between particles in the low dimensional small systems can lead to many unexpected effects. We considered electrons in a Luttinger liquid, in a superconducting state, and atoms in a magneto-optical trap. Using bosonization techniques we calculated the thermopower of a Luttinger liquid wire with an impurity. We predicted the appearance of a phase dependent force and resonant phase dependent magnetization in the nanoscopic superconductor - normal metal superconductor (or superconductor - two dimensional electron gas - superconductor) junction. We also considered plasma oscillations inside thin superconducting tubes and rings and predicted that the velocities of the plasmons in these systems are periodic functions of the magnetic flux. By considering neutral atoms in a harmonic trap we discovered that strongly repelling atoms do not form Bose-Einstein condensate at zero temperature but tend to occupy different orbitals with small mutual overlap, forming crystallite structures similar to Wigner molecules of electrons inside a quantum dot.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-10-16T17:40:13Z No. of bitstreams: 1 GILSON ACIOLE RODRIGUES – DISSERTAÇÃO (PPGFísica) 2016.pdf: 1524954 bytes, checksum: 9054f2fa535b67f3184b1f692caa7c88 (MD5) / Made available in DSpace on 2018-10-16T17:40:13Z (GMT). No. of bitstreams: 1 GILSON ACIOLE RODRIGUES – DISSERTAÇÃO (PPGFísica) 2016.pdf: 1524954 bytes, checksum: 9054f2fa535b67f3184b1f692caa7c88 (MD5) Previous issue date: 2016-09-28 / Capes / A influência dos deslocamentos parafuso em sistemas quânticos tem recebido considerável atenção nos últimos anos. Alguns trabalhos são baseados na teoria geométrica de defeitos em semicondutores e desenvolvidos por Katanaev Volovich. Nesta abordagem, o semicondutor com um deslocamento parafuso é descrito por uma variedade de Riemann-Cartan onde o deslocamento parafuso está associado ao vetor Burgers. Neste limite do contínuo, um deslocamento parafuso afeta um sistema quântico como um tubo de fluxo magnético isolado, causando fenômenos de interferência tipo Aharonov-Bohm (AB). O espectro de energia de elétrons em torno deste tipo de defeito mostra uma configuração semelhante a do sistema AB. Neste trabalho, investigamos a influência de um deslocamento parafuso sobre os níveis de energia e as funções de onda de um elétron confinado em um potencial pseudo-harmônico bidimensional (2D) sob a influência de um campo magnético externo para o ponto quântico e campo Aharonov-Bohm para um pseudo-ponto quântico. As soluções exatas para autovalores de energia e funções de onda são computadas em função do campo magnético uniforme, fluxo Aharonov-Bohm, número quântico magnético e do parâmetro que caracteriza o deslocamento parafuso, o vetor Burgers. Foram investigadas as modificações devido à deslocação parafuso no coeficiente de absorção de luz e na frequência de absorção limiar. Descobrimos que conforme o vetor Burgers aumenta, as curvas de frequência são impusionadas para cima em direção ao crescimento do mesmo. Um aspecto interessante que observamos é que o fluxo Aharonov-Bohm pode ser ajustado de forma a cancelar o efeito do deslocamento parafuso. / The influence of screw dislocations in quantum systems has received considerable attention in recent years. Some works are based on the geometric theory of defects in semiconductors and developed by Katanaev Volovich. In this approach the semiconductor with a screw dislocation is described by a variety of Riemann-Cartan where the screw dislocation is associated with the Burgers vector. This limit of the continuum, a screw displacement affects a quantum system as an isolated magnetic flux tube, causing phenomena of interference type Aharonov-Bohm (AB). The electron energy spectrum around this type of defect shows a configuration similar to the AB system. In this work, we investigated the influence of a screw dislocation on the energy levels and the wavefunctions of an electron confined in a two-dimensional pseudoharmonic quantum dot under the influence of an external magnetic field inside a dot and Aharonov-Bohm field inside a pseudodot. The exact solutions for energy eigenvalues and wavefunctions are computed as functions of applied uniform magnetic field strength, Aharonov-Bohm flux, magnetic quantum number and the parameter characterizing the screw dislocation, the Burgers vector. We investigate the modifications due to the screw dislocation on the light interband absorption coefficient and absorption threshold frequency. We found that as the Burgers vector increases, the curves of frequency are pushed up towards of the growth of it. One interesting aspect which we have observed is that the Aharonov-Bohm flux can be tuned in order to cancel the screw effect of the model.

Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-13T11:51:46Z No. of bitstreams: 1 arquivototal.pdf: 831966 bytes, checksum: a9f68724ebd2fdd53f6f561f0f45d42c (MD5) / Made available in DSpace on 2017-09-13T11:51:46Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 831966 bytes, checksum: a9f68724ebd2fdd53f6f561f0f45d42c (MD5) Previous issue date: 2013-02-01 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Inertial effects, such as Coriolis’ and centrifuge forces play an interesting role on classical mechanics and currently has been largely used in quantum mechanics, including in analogies with the electromagnetic effects. However, these analogies between the inertial forces on the massives particules and the electromagnetic forces on charged particles is not new. They were explored by Aharonov and Carmi in 1970 and by Tsai and Nelson in 1988 in the context of a rotational quantum phase like an Aharonov-Bohm phase. Based in this analogy, Dattoli and Quattromini, introduced Coriolis’ analogue quantum states to Landau levels. In 1915, Barnett had already published a paper about magnetization due to rotation which recently had a renewed interest applyed to nanostructures. A rotational analogy of the classical Hall effect was proposed and rotational inertial forces were studied in spintronic. Energy spectra like Landau levels appear under the action of Coriolis forces when the centrifuge force acting on free electrons is compensated by a radial electric field. In this work, we will demonstrate effects caused by rotation and magnetic field in a spinning conductor disc. We will study both the electromagnetic and inertial interactions simultaneously. Some values to the relation between the magnetic field and the rotation will be chosen and this will result in Landau-like levels to a system with resultant force composed by Coriolis’ and magnetic forces. A similar behavior for the energy spectrum will be found without a magnetic force composing the resultant force. / Efeitos inerciais, tais como a força centrífuga e a de Coriolis, desempenham um papel importante na mecânica clássica e atualmente têm sido amplamente explorados na mecânica quântica, inclusive em analogias com efeitos eletromagnéticos. No entanto, essas analogias entre as forças inerciais sobre partículas massivas e as forças electromagnéticas sobre partículas carregadas não é nenhuma novidade. Elas foram exploradas por Aharonov e Carmi em 1970 e por Tsai e Neilson em 1988 no contexto de uma fase quântica rotacional similar à fase de Aharonov- Bohm. Baseados nessa mesma analogia, Dattoli e Quattromini introduziram estados quânticos de Coriolis análogos aos níveis de Landau. Em 1915, Barnett já havia publicado um artigo sobre magnetização devido à rotação o qual teve recentemente um interesse renovado aplicado a nanoestruturas. Um análogo rotacional do efeito Hall clássico foi proposto e os efeitos inerciais da rotação foram estudados em spintrônica. Espectros de energia tipo níveis de Landau aparecem sob a ação da força de Coriolis quando a força centrífuga agindo nos elétrons livres é compensada por um campo elétrico radial. Neste trabalho, vamos demonstrar efeitos devido à rotação e ao campo magnético em um disco condutor girante. Estudaremos as interações eletromagnéticas e inerciais simultaneamente. Alguns valores para a relação entre o campo magnético e a rotação serão escolhidos e resultarão em níveis tipo Landau para um sistema com força resultante composta pelas forças de Coriolis e magnética. Um mesmo comportamento para o espectro de energia será obtido sem força magnética compondo a força resultante.

Made available in DSpace on 2015-05-14T12:14:05Z (GMT). No. of bitstreams: 1 Arquivototal.pdf: 5046450 bytes, checksum: bd56c31f5c1b1739dfc96f350ac77b34 (MD5) Previous issue date: 2010-10-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work we discuss the importance of the quantum phases using the Aharonov-Bohm Effect for charged particles and neutral particles with magnetic dipole moment(Aharonov- Casher Effect) and electric dipole moment(He-McKellar-Wilkens Effect) and atoms with electric quadrupole moment. It takes advantage of the initial study of such systems to show the emergence of Landau levels in the dynamics of a particle in two situations: when the particle is charged and when it is neutral. In the case of a neutral particle is considered that it possesses electric dipole moment. In addition it is the first time which is approached a neutral atom with electric quadrupole moment. / Neste trabalho discutimos a importância das fases quânticas usando o Efeito Aharonov-Bohm para partículas carregadas e partículas neutras com momento de dipolo magnético (Efeito Aharonov-Casher) e momento de dipolo elétrico (Efeito He-McKellar-Wilkens), e átomos com momento de quadrupolo elétrico. Tira-se vantagem do estudo inicial de tais sistemas para mostrar a emersão de níveis de Landau na dinâmica de uma partícula em duas situações: quando a partícula está carregada e quando ela é neutra. No caso de uma partícula neutra é considerado que esta possui momento de dipolo elétrico. Além disso é a primeira vez que é abordado um átomo neutro com momento de quadrupolo elétrico.

Cette thèse est consacrée à l’étude expérimentale des propriétés magnéto-optiques intrinsèques des nanotubes de carbone mono-paroi par spectroscopie de photoluminescence résolue en temps.Un dispositif de microscopie optique confocale de grande ouverture numérique (NA = 0.95),incluant un cryostat magnétique, permet l’étude de nanotubes suspendus à l’échelle individuelle,à température cryogénique (jusqu’à 2 Kelvin) et sous champ magnétique (jusqu’à 7 Tesla). L’évolution des spectres et des déclins de photoluminescence avec le champ magnétique montre l’influence de l’effet Aharonov-Bohm sur les deux excitons singulets de plus basse énergie, c’est à-dire l’exciton fondamental qui est optiquement inactif (exciton noir) et un exciton d’énergie supérieure séparé de quelques milliélectronvolts qui est optiquement actif (exciton brillant). L’interprétation de ces résultats à partir d’un modèle d’équations de taux qui intègre le couplage Aharonov-Bohm entre ces deux excitons permet de déterminer séparément les durées de vie excitoniques et de fournir des informations quantitatives sur la relaxation de l’énergie depuis les niveaux supérieurs photo-excités. La relaxation de l’énergie suite à la photo-excitation de la transition S22 conduit à une efficacité de peuplement de l’état brillant quatre fois plus faible que celle de l’état noir, mais qui augmente significativement lorsque la relaxation se produit depuis les niveaux excitoniques KK’. D’autre part, le bon rapport signal à bruit obtenu dans les spectres de photoluminescence permet de révéler l’existence d’un couplage intrinsèque en champ nul entre l’exciton noir et l’exciton brillant ainsi que le maintien de la mobilité excitonique dans les nanotubes suspendus à la température de l’hélium liquide. / This thesis is dedicated to the experimental study of the intrinsic magneto-optical properties of single-walled carbon nanotubes through time-resolved photoluminescence spectroscopy. Measurements are performed on suspended nanotubes samples at the single-object level using a home-built confocal optical microscope with a large numerical aperture (NA = 0.95) operating at cryogenic temperature (down to 2K) and high magnetic field (up to 7T). The evolution of the photoluminescence spectra and decay signals with increasing magnetic fields shows the influence of the Aharonov-Bohm effect on the two lowest-energy singlet excitons, namely the ground exciton which is optically inactive (dark exciton) and an exciton lying a few millielectron volts higher in energy which is optically active (bright exciton). A model of these results based on rate equations and including the Aharonov-Bohm coupling between these two excitons enables to determine separately the excitons lifetimes and to derive quantitative information on the energy relaxation from the photo-excited higher levels. The energy relaxation following the photo-excitation of the S22 transition leads to a bright state population efficiency four times lower than that of the dark state, but it significantly increases when energy relaxation occurs from the KK’ excitonic levels. Thanks to a good signal to noise ratio, the photoluminescence spectra also reveal the presence of an intrinsic zero-field coupling between the dark and the brightexcitons, as well as an excitonic mobility preserved at liquid helium temperature in suspended nanotubes.