Orientadores: Peter Alexander Bleinroth Schulz, Ana Luiza Cardoso Pereira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-17T03:19:21Z (GMT). No. of bitstreams: 1 Munoz_WilliamArmando_M.pdf: 8434738 bytes, checksum: d59e43facc73d2ca570f8291de7f22cc (MD5) Previous issue date: 2010 / Resumo: Nós estudamos os efeitos da quebra de simetria e de desordem no espectro de energia de um elétron numa bicamada de grafeno. O problema foi abordado através de simulações numéricas considerando um Hamiltoniano tight-binding para uma rede retangular topologicamente equivalente à rede hexagonal do grafeno que nos permite incluir de forma simples os efeitos do campo magnético através da substituição de Peierls. O problema de quebra de simetria foi observado quando consideramos a aplicação de uma diferença de potencial entre as camadas. Neste contexto, é observada uma quebra completa na degenerescência do nível de Landau de energia zero devida à aplicação desta diferença de potencial entre as camadas. Acompanhamos este mecanismo de quebra de degenerescência para uma situação onde a diferença de potencial entre camadas é mantida fixa enquanto o campo magnético é aumentado. Isto mostra a possibilidade de controlar a abertura de gaps através da variação do campo magnético na bicamada de grafeno e está de acordo com o que foi recentemente observado experimentalmente. Observamos também um comportamento para a separação em energia desta quebra de degenerescência do tipo vB para valores do campo magnético B<60 Teslas, enquanto que para campos maiores é obtido um comportamento assintótico para energias próximas da separação (Vg) do desdobramento do nível de Landau central. Um mapeamento das funções de onda dos estados envolvidos nesta quebra de degenerescência, mostra um esquema diferente para regimes diferentes de campo magnético. Conseguimos verificar claramente como a quebra da degenerescência do nível de Landau central está relacionada com uma quebra da degenerêscencia entre as duas camadas da bicamada e também entre as duas sub-redes que formam o grafeno. O segundo problema abordado neste trabalho é relacionado à introdução de duas vacâncias acopladas na bicamada de grafeno. Em presença de um campo magnético perpendicular ao plano das camadas mostramos como estados localizados ao redor do defeito com energias entre os níveis de Landau são introduzidos pela presença das vacâncias acopladas. Estes estados para baixas energias formam uma molécula de vacâncias que pode ser facilmente polarizável pela aplicação de um potencial entre as camadas / Abstract: We studied the symmetry breaking and disorder effects on energy spectrum of an electron in a bilayer graphene. We used numerical calculation considering a 2D tight-binding model for a rectangular lattice which not changes the hexagonal lattice topology and where the magnetic field effects are easily calculated. The breaking symmetry problem was considered through the application of a potential difference between both layers in the bilayer graphene. In this case, we observe a complete degeneracy breaking of the energy-zero Landau level due to the application of this potential difference between the two layers. We followed this degeneracy breaking considering a potential difference constant while the magnetic field was increasing. That shows a possibility to control the opening of the gap by means of the magnetic fields in the bilayer graphene which is in agreement with recent experimental results. We also shown that this gap increases with a root of B for values of B<60T, while in the high magnetic field regime (B>60T) the energy dependency of the gap shows a asymptotic behavior with B, which tends to energy values close to Vg. We mapped the wave functions amplitudes of states related to the splitting of the zero-energy Landau level and we found that this electronic charge distribution is different depending on magnetic field regime. We verified clearly as this splitting is related to a layers degeneracy breaking as well as a sublattice (valley) degeneracy breaking. The second problem considered in this thesis is related to the introduction of two coupled vacancies in the bilayer graphene. In presence of a perpendicular magnetic field, we show that two coupled vacancies in the bilayer graphene introduce states with a charge-density distribution localized close to the defect and energies between consecutives Landau levels. These states for lowest energies form a vacancy molecule which can be easily polarized by applying of a potential between the two layers in bilayer graphene / Mestrado / Física da Matéria Condensada / Mestre em Física

Orientadores: Ana Luiza Cardoso Pereira, Luiz Eduardo Moreira Carvalho de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T09:45:49Z (GMT). No. of bitstreams: 1 SolisLerma_DanielAlejandro_M.pdf: 11339360 bytes, checksum: 0efee568f2b70411f8fcb14075392b26 (MD5) Previous issue date: 2015 / Resumo: Neste trabalho foram estudados os efeitos de bordas com terminações perfeitamente definidas de uma rede de grafeno no regime Hall quântico sobre as propriedades eletrônicas deste sistema. O problema foi abordado com uso da aproximação tight-binding incluindo os efeitos do campo magnético e desordem no modelo. Estudou-se primeiramente o efeito das bordas nos níveis de energia do sistema, em espectros tipo borboleta de Hofstadter. Então o foco foi analisar as propriedades de localização eletrônica dos estados de borda, e as particularidades da distribuição das funções de onda nestes casos. Para investigar os estados de borda e determinar, para cada um dos estados eletrônicos, o quanto da função de onda encontra-se localizada nas bordas, foi criada uma quantidade nomeada Edge Fraction, denida como a somatória das amplitudes da função de onda na região das bordas, que numa aproximação semiclássica foi aqui considerada como a região delimitada por uma distância 2'B das bordas, onde 'B é o comprimento magnético. Com o uso do Edge Fraction, analisando-se as contribuições armchair e zigzag separadamente, em redes de grafeno quadradas, encontrou-se que há regiões de energia onde as funções de onda claramente cam mais localizadas num determinado tipo de borda. Este comportamento presume-se que é produto da competição que existe entre os potenciais devidos à presença de bordas e desordem no sistema, que evidenciam-se também no espectro de energia tipo borboleta de Hofstadter. Os resultados obtidos contribuem para o entendimento das propriedades de localização em redes de grafeno com bordas / Abstract: In this work the effects of sharp edges in the electronic properties of graphene lattices in the quantum Hall regime were studied. The problem was addressed using the tight-binding approximation including the effects of the magnetic eld and disorder in the model. It was studied at rst the effect of the edges in the energy levels of the system, through Hofstadter's buttery-like spectrum. Then we focused on analysing the localization properties of edge states and the particularities of the wave function distributions for these cases. To investigate the edge states and to determine, for each electronic state, how much of the wave function is localized at the edges, it was created a quantity called Edge Fraction. This quantity was dened as the probability density sum in the edge region, which in a semi-classical approximation, was considered here as the region limited by a distance 2'B from the edges, where 'B is the magnetic length. Using the Edge Fraction and analysing the contributions of armchair and zigzag edges separately, in squared lattices, it was found that there are energy regions where the wave functions are clearly more localized in a specic edge type. This behaviour is believed to be a result of the competition between the potential due to the presence of the edge and the potential due to the disorder in the system, which are also present in the Hofstadter energy spectrum. The results obtained contribute to the understanding of the localization properties of graphene lattices with edges / Mestrado / Física / Mestre em Física / 1247644 / CAPES

The generation and propagation of pulses of nonequilibrium acoustic phonons and their interaction with semiconductor nanostructures are investigated. Such studies can give unique information about the properties of low-dimensional electron systems, but in order to interpret the experiments and to understand the underlying physics, a comparison with theoretical models is absolutely necessary. A central point of this work is therefore a universal theoretical approach allowing the simulation and the analysis of phonon spectroscopy measurements on low-dimensional semiconductor structures. The model takes into account the characteristic properties of the considered systems. These properties are the elastic anisotropy of the substrate material leading to focusing effects and highly anisotropic phonon propagation, the anisotropic nature of the different electron-phonon coupling mechanisms, which depend manifestly on phonon wavevector direction and polarization vector, and the sensitivity to the confinement parameters of the low-dimensional electron systems. We show that screening of the electron-phonon interaction can have a much stronger influence on the results of angle-resolved phonon spectroscopy than expected from transport measurements. Since we compare theoretical simulations with real experiments, the geometrical arrangement and the spatial extension of phonon source and detector are also included in the approach enabling a quantitative analysis of the data this way. To illustrate the influence of acoustic anisotropy and carrier confinement on the results of phonon spectroscopy in detail we analyse two different applications. In the first case the low-dimensional electron system acts as the phonon detector and the phonon induced drag current is measured. Our theoretical model enables us to calculate the electric current induced in low-dimensional electron systems by pulses of (ballistic) nonequilibrium phonons. The theoretical drag patterns reproduce the main features of the experimental images very well. The sensitivity of the results to variations of the confining potential of quasi-2D and quasi-1D electrons is demonstrated. This provides the opportunity to use phonon-drag imaging as unique experimental tool for determining the confinement lengths of low-dimensional electron systems. By comparing the experimental and theoretical images it is also possible to estimate the relative strength of the different electron-phonon coupling mechanisms.In the second application the low-dimensional electron system acts as the phonon pulse source and the angle and mode dependence of the acoustic phonon emission by hot 2D electrons is investigated. The results exhibit strong variations in the phonon signal as a function of the detector position and depend markedly on the coupling mechanism, the phonon polarization and the electron confinement width. We demonstrate that the ratio of the strengths of the emitted longitudinal (LA) and transverse (TA) acoustic phonon modes is predicted correctly only by a theoretical model that properly includes the effects of acoustic anisotropy on the electron-phonon matrix elements, the screening, and the form of the confining potential. A simple adoption of widely used theoretical assumptions, like the isotropic approximation for the phonons in the electron-phonon matrix elements or the use of simple variational envelope wavefunctions for the carrier confinement, can corrupt or even falsify theoretical predictions.We explain the `mystery of the missing longitudinal mode' in heat-pulse experiments with hot 2D electrons in GaAs/AlGaAs heterojunctions. We demonstrate that screening prevents a strong peak in the phonon emission of deformation potential coupled LA phonons in a direction nearly normal to the 2D electron system and that deformation potential coupled TA phonons give a significant contribution to the phonon signal in certain emission directions. / Die vorliegende Arbeit beschäftigt sich mit der Ausbreitung von akustischen Nichtgleichgewichtsphononen und deren Wechselwirkung mit Halbleiter-Nanostrukturen. Güte und Effizienz moderner Halbleiter-Bauelemente hängen wesentlich vom Verständnis der Wechselwirkung akustischer Phononen mit niederdimensionalen Elektronensystemen ab. Traditionelle Untersuchungsmethoden, wie die Messung der elektrischen Leitfähigkeit oder der Thermospannung, erlauben nur eingeschränkte Aussagen. Sie mitteln über die beteiligten Phononenmoden und eine Trennung der einzelnen Wechselwirkungsmechanismen ist nur näherungsweise möglich ist. Demgegenüber erlaubt die in der Arbeit diskutierte Methode der winkel- und zeitaufgelösten Phononen-Spektroskopie ein direktes Studium des Beitrags einzelner Phononenmoden, d.h. in Abhängigkeit von Wellenzahlvektor und Polarisation der Phononen. Im Mittelpunkt der Arbeit steht die Fragestellung, wie akustische Anisotropie und Ladungsträger-Confinement die Ergebnisse der winkel- und zeitaufgelösten Phononen-Spektroskopie beeinflussen und prägen. Dazu wird ein umfassendes theoretisches Modell zur Simulation von Phononen-Spektroskopie-Experimenten an niederdimensionalen Halbleitersystemen vorgestellt. Dieses erlaubt sowohl ein qualitatives Verständnis der ablaufenden physikalischen Prozesse als auch eine quantitative Analyse der Messergebnisse. Die Vorteile gegenüber anderen Modellen und Rechnungen liegen dabei in dem konsequenten Einbeziehen der akustischen Anisotropie, nicht nur für die Ausbreitung der Phononen, sondern auch für die Matrixelemente der Wechselwirkung, sowie eine saubere Behandlung des Confinements der Elektronen in den niederdimensionalen Systemen. Dabei werden die Grenzen weit verbreiteter Näherungsansätze für die Elektron-Phonon-Matrixelemente und das Elektronen-Confinement deutlich aufgezeigt. Für den quantitativen Vergleich mit realen Experimenten werden aber auch solche Größen, wie die endliche räumliche Ausdehnung von Phononenquelle und Detektor, die Streuung der Phononen an Verunreinigungen oder die Abschirmung der Elektron-Phonon-Kopplung durch die Elektron-Elektron-Wechselwirkung berücksichtigt.Im zweiten Teil der Arbeit wird der theoretische Apparat auf typische experimentelle Fragestellungen angewandt. Im Falle der Phonon-Drag-Experimente an GaAs/AlGaAs Heterostrukturen wird der durch akustische Nichtgleichgewichtsphononen in zwei- und eindimensionalen Elektronensystemen induzierte elektrische Strom (Phonon-Drag-Strom) als Funktion des Ortes der Phononenquelle bestimmt. Das in der Arbeit hergeleitete theoretische Modell kann die experimentellen Resultate für die Winkelabhängigkeit des Drag-Stromes sowohl für Messungen mit und ohne Magnetfeld qualitativ gut beschreiben. Außerdem wird der Einfluss unterschiedlicher Confinementmodelle und unterschiedlicher Wechselwirkungsmechanismen studiert. Dadurch ist es möglich, aus Phonon-Drag-Messungen Rückschlüsse auf die elektronischen und strukturellen Eigenschaften der niederdimensionalen Elektronensysteme zu ziehen (Fermivektor, effektive Masse, Elektron-Phonon-Kopplungskonstanten, Form des Confinementpotentials). Als weiteres Anwendungsbeispiel wird das Problem der Energierelaxation (aufgeheizter)zweidimensionaler Elektronensysteme in GaAs Heterostrukturen und Quantentrögen untersucht. Für Elektronentemperaturen unterhalb 50 K werden die Gesamtemissionsrate als Funktion der Temperatur und die winkelaufgelöste Emissionsrate (als Funktion der Detektorposition) berechnet. Für beide Größen wird erstmals eine gute Übereinstimmung zwischen Theorie und Experiment gefunden. Es zeigt sich, dass akustische Anisotropie und Abschirmungseffekte zu überraschenden neuen Ergebnissen führen können. Ein Beispiel dafür ist der unerwartet große Beitrag der mittels Deformationspotential-Wechselwirkung emittierten transversalen akustischen Phononen, der bei einer Emission der Phononen näherungsweise senkrecht zum zweidimensionalen System beobachtet werden kann.

Orientadores: Peter A. B. Schulz, John T. Chalker / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-06T19:00:22Z (GMT). No. of bitstreams: 1 Pereira_AnaLuizaCardoso_D.pdf: 2880300 bytes, checksum: ffd133973b4bc6e23c91694bc47d8794 (MD5) Previous issue date: 2005 / Resumo: Esse trabalho é dedicado ao estudo de dois problemas de interesse atual em sistemas quânticos de baixa dimensionalidade. Ambos são relacionados ao processo de localização eletrônica no regime Hall quântico. O primeiro problema diz respeito ao destino dos estados estendidos no limite de baixos campos magnéticos ou forte desordem, onde ocorre a transição de líquido de Hall para o isolante de Hall. O problema é abordado através de simulações numéricas, com um modelo de rede bidimensional tratado por um Hamiltoniano tight-binding, considerando-se tanto desordem tipo ruído branco quanto desordem correlacionada com perfil Gaussiano. Nós observamos que à medida que o campo magnético tende a zero ou a desordem é suficientemente aumentada no sistema, os estados estendidos sofrem um deslocamento em relação ao centro das bandas de Landau, indo em direção às mais altas energias e, eventualmente, ultrapassando a energia de Fermi. Esse mecanismo é chamado na literatura de levitação de estados estendidos. Nossos resultados permitem uma análise quantitativa. Identificamos os seguintes parâmetros como sendo os relevantes para mapear a levitação: (i) a razão entre escalas de energia ¿ entre a energia de separação dos níveis de Landau e o alargamento do nível devido à desordem; e (ii) a razão entre escalas de comprimento ¿ entre o comprimento magnético e o comprimento de correlação da desordem. Analisando uma vasta gama de parâmetros, uma expressão de escala descrevendo a levitação de estados estendidos é estabelecida neste trabalho. O segundo problema abordado nesta tese é relacionado ao processo de blindagem do potencial de desordem e ao mecanismo de formação dos estados localizados em sistemas Hall quânticos. O trabalho analítico apresentado aqui é motivado por recentes resultados experimentais, que mostram imagens de microscopia com medidas locais do potencial eletrostático e da compressibilidade desses sistemas, evidenciando como se dá o processo de carga de estados localizados por cargas inteiras ou fracionárias (quase-partículas). Em um regime onde o comportamento é dominado por interações Coulombianas, estabelecemos um modelo eletrostático que descreve o estado localizado como sendo uma região compressível (quantum dot ou antidot) envolta por um plano incompressível, usando a aproximação de Thomas-Fermi para tratar as interações. O potencial eletrostático nas vizinhanças da região compressível é calculado, fornecendo o tamanho dos saltos que ocorrem no potencial à medida que cada carga é adicionada ou removida do estado localizado. Além de mostrar como estes saltos se tornam menores com o aumento do índice de Landau, nossos resultados mostram a dependência deles com a altura de observação do potencial (ou seja, a altura da ponta de prova em relação ao gás de elétrons). O modelo apresentado pode ser usado para tratar estados localizados observados nos platôs do efeito Hall quântico inteiro ou fracionário / Abstract: This work is devoted to the study of two problems of current interest in low dimensional quantum systems. Both are related to the process of electron localization in the quantum Hall regime. The first problem refers to the fate of extended states in the limit of low magnetic fields or strong disorder, where the transition from quantum Hall liquid to Hall insulator takes place. A numerical approach to the problem is used, with a 2D lattice model treated in a tight-binding framework, considering both white-noise and Gaussian correlated disorder. We observe that as the magnetic field vanishes or the disorder is sufficiently increased in the system, the extended states are shifted from the Landau band centers, going to higher energies and, eventually, rising above the Fermi energy. This mechanism is referred in the literature as levitation of extended states. Our results allow a quantitative analysis. We identify the following parameters as the relevant ones to map the levitation: (i) the energy scales ratio - between the energy separation of consecutive Landau levels and the level broadening due to disorder; and (ii) the length scales ratio - between the magnetic length and the disorder correlation length. Analyzing a wide range of parameters, a scaling expression describing the levitation of extended states is established. The second problem considered in this thesis is related to the screening of the disorder potential and to the mechanism of formation of localized states in quantum Hall systems. The analytical work we present here is motivated by recent imaging experiments, which probe locally the electrostatic potential and the compressibility of these systems, showing the charging of individual localized states by integer or fractional charges (quasiparticles). For a regime where the behavior is dominated by Coulomb interactions, we set out an electrostatic model describing the localized state as a compressible region (quantum dot or antidot) embebed in an incompressible background, using the Thomas-Fermi approximation to treat the interactions. The electrostatic potential in the vicinity of the compressible region is calculated, providing the size of potential steps as each charge is added or removed from the localized state. Besides from showing how the potential steps get smaller for higher Landau levels, our results show the dependence of these steps with the height of observation (i.e., the distance from the scanning probe to the electron gas). The proposed model can be used to treat localized states observed on integer or fractional quantum Hall plateaus / Doutorado / Física da Matéria Condensada / Doutor em Ciências

The generation and propagation of pulses of nonequilibrium acoustic phonons and their interaction with semiconductor nanostructures are investigated. Such studies can give unique information about the properties of low-dimensional electron systems, but in order to interpret the experiments and to understand the underlying physics, a comparison with theoretical models is absolutely necessary. A central point of this work is therefore a universal theoretical approach allowing the simulation and the analysis of phonon spectroscopy measurements on low-dimensional semiconductor structures. The model takes into account the characteristic properties of the considered systems. These properties are the elastic anisotropy of the substrate material leading to focusing effects and highly anisotropic phonon propagation, the anisotropic nature of the different electron-phonon coupling mechanisms, which depend manifestly on phonon wavevector direction and polarization vector, and the sensitivity to the confinement parameters of the low-dimensional electron systems. We show that screening of the electron-phonon interaction can have a much stronger influence on the results of angle-resolved phonon spectroscopy than expected from transport measurements. Since we compare theoretical simulations with real experiments, the geometrical arrangement and the spatial extension of phonon source and detector are also included in the approach enabling a quantitative analysis of the data this way. To illustrate the influence of acoustic anisotropy and carrier confinement on the results of phonon spectroscopy in detail we analyse two different applications. In the first case the low-dimensional electron system acts as the phonon detector and the phonon induced drag current is measured. Our theoretical model enables us to calculate the electric current induced in low-dimensional electron systems by pulses of (ballistic) nonequilibrium phonons. The theoretical drag patterns reproduce the main features of the experimental images very well. The sensitivity of the results to variations of the confining potential of quasi-2D and quasi-1D electrons is demonstrated. This provides the opportunity to use phonon-drag imaging as unique experimental tool for determining the confinement lengths of low-dimensional electron systems. By comparing the experimental and theoretical images it is also possible to estimate the relative strength of the different electron-phonon coupling mechanisms.In the second application the low-dimensional electron system acts as the phonon pulse source and the angle and mode dependence of the acoustic phonon emission by hot 2D electrons is investigated. The results exhibit strong variations in the phonon signal as a function of the detector position and depend markedly on the coupling mechanism, the phonon polarization and the electron confinement width. We demonstrate that the ratio of the strengths of the emitted longitudinal (LA) and transverse (TA) acoustic phonon modes is predicted correctly only by a theoretical model that properly includes the effects of acoustic anisotropy on the electron-phonon matrix elements, the screening, and the form of the confining potential. A simple adoption of widely used theoretical assumptions, like the isotropic approximation for the phonons in the electron-phonon matrix elements or the use of simple variational envelope wavefunctions for the carrier confinement, can corrupt or even falsify theoretical predictions.We explain the `mystery of the missing longitudinal mode' in heat-pulse experiments with hot 2D electrons in GaAs/AlGaAs heterojunctions. We demonstrate that screening prevents a strong peak in the phonon emission of deformation potential coupled LA phonons in a direction nearly normal to the 2D electron system and that deformation potential coupled TA phonons give a significant contribution to the phonon signal in certain emission directions. / Die vorliegende Arbeit beschäftigt sich mit der Ausbreitung von akustischen Nichtgleichgewichtsphononen und deren Wechselwirkung mit Halbleiter-Nanostrukturen. Güte und Effizienz moderner Halbleiter-Bauelemente hängen wesentlich vom Verständnis der Wechselwirkung akustischer Phononen mit niederdimensionalen Elektronensystemen ab. Traditionelle Untersuchungsmethoden, wie die Messung der elektrischen Leitfähigkeit oder der Thermospannung, erlauben nur eingeschränkte Aussagen. Sie mitteln über die beteiligten Phononenmoden und eine Trennung der einzelnen Wechselwirkungsmechanismen ist nur näherungsweise möglich ist. Demgegenüber erlaubt die in der Arbeit diskutierte Methode der winkel- und zeitaufgelösten Phononen-Spektroskopie ein direktes Studium des Beitrags einzelner Phononenmoden, d.h. in Abhängigkeit von Wellenzahlvektor und Polarisation der Phononen. Im Mittelpunkt der Arbeit steht die Fragestellung, wie akustische Anisotropie und Ladungsträger-Confinement die Ergebnisse der winkel- und zeitaufgelösten Phononen-Spektroskopie beeinflussen und prägen. Dazu wird ein umfassendes theoretisches Modell zur Simulation von Phononen-Spektroskopie-Experimenten an niederdimensionalen Halbleitersystemen vorgestellt. Dieses erlaubt sowohl ein qualitatives Verständnis der ablaufenden physikalischen Prozesse als auch eine quantitative Analyse der Messergebnisse. Die Vorteile gegenüber anderen Modellen und Rechnungen liegen dabei in dem konsequenten Einbeziehen der akustischen Anisotropie, nicht nur für die Ausbreitung der Phononen, sondern auch für die Matrixelemente der Wechselwirkung, sowie eine saubere Behandlung des Confinements der Elektronen in den niederdimensionalen Systemen. Dabei werden die Grenzen weit verbreiteter Näherungsansätze für die Elektron-Phonon-Matrixelemente und das Elektronen-Confinement deutlich aufgezeigt. Für den quantitativen Vergleich mit realen Experimenten werden aber auch solche Größen, wie die endliche räumliche Ausdehnung von Phononenquelle und Detektor, die Streuung der Phononen an Verunreinigungen oder die Abschirmung der Elektron-Phonon-Kopplung durch die Elektron-Elektron-Wechselwirkung berücksichtigt.Im zweiten Teil der Arbeit wird der theoretische Apparat auf typische experimentelle Fragestellungen angewandt. Im Falle der Phonon-Drag-Experimente an GaAs/AlGaAs Heterostrukturen wird der durch akustische Nichtgleichgewichtsphononen in zwei- und eindimensionalen Elektronensystemen induzierte elektrische Strom (Phonon-Drag-Strom) als Funktion des Ortes der Phononenquelle bestimmt. Das in der Arbeit hergeleitete theoretische Modell kann die experimentellen Resultate für die Winkelabhängigkeit des Drag-Stromes sowohl für Messungen mit und ohne Magnetfeld qualitativ gut beschreiben. Außerdem wird der Einfluss unterschiedlicher Confinementmodelle und unterschiedlicher Wechselwirkungsmechanismen studiert. Dadurch ist es möglich, aus Phonon-Drag-Messungen Rückschlüsse auf die elektronischen und strukturellen Eigenschaften der niederdimensionalen Elektronensysteme zu ziehen (Fermivektor, effektive Masse, Elektron-Phonon-Kopplungskonstanten, Form des Confinementpotentials). Als weiteres Anwendungsbeispiel wird das Problem der Energierelaxation (aufgeheizter)zweidimensionaler Elektronensysteme in GaAs Heterostrukturen und Quantentrögen untersucht. Für Elektronentemperaturen unterhalb 50 K werden die Gesamtemissionsrate als Funktion der Temperatur und die winkelaufgelöste Emissionsrate (als Funktion der Detektorposition) berechnet. Für beide Größen wird erstmals eine gute Übereinstimmung zwischen Theorie und Experiment gefunden. Es zeigt sich, dass akustische Anisotropie und Abschirmungseffekte zu überraschenden neuen Ergebnissen führen können. Ein Beispiel dafür ist der unerwartet große Beitrag der mittels Deformationspotential-Wechselwirkung emittierten transversalen akustischen Phononen, der bei einer Emission der Phononen näherungsweise senkrecht zum zweidimensionalen System beobachtet werden kann.