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1
Foley, Simon Timothy. "Effects of electron-electron interactions on electronic transport in disordered systems." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273932.
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Sergueev, Nikolai. "Electron-phonon interactions in molecular electronic devices." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102171.
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Over the past several decades, semiconductor electronic devices have been miniaturized following the remarkable "Moores law". If this trend is to continue, devices will reach physical size limit in the not too distance future. There is therefore an urgent need to understand the physics of electronic devices at nano-meter scale, and to predict how such nanoelectronics will work. In nanoelectronics theory, one of the most important and difficult problems concerns electron-phonon interactions under nonequilibrium transport conditions. Calculating phonon spectrum, electron-phonon interaction, and their effects to charge transport for nanoelectronic devices including all atomic microscopic details, is a very difficult and unsolved problem. It is the purpose of this thesis to develop a theoretical formalism and associated numerical tools for solving this problem.In our formalism, we calculate electronic Hamiltonian via density functional theory (DFT) within the nonequilibrium Green's functions (NEGF) which takes care of nonequilibrium transport conditions and open device boundaries for the devices. From the total energy of the device scattering region, we derive the dynamic matrix in analytical form within DFT-NEGF and it gives the vibrational spectrum of the relevant atoms. The vibrational spectrum together with the vibrational eigenvector gives the electron-phonon coupling strength at nonequilibrium for various scattering states. A self-consistent Born approximation (SCBA) allows one to determine the phonon self-energy, the electron Green's function, the electronic density matrix and the electronic Hamiltonian, all self-consistently within equal footing. The main technical development of this work is the DFT-NEGF-SCBA formalism and its associated codes.
A number of important physics issues are studied in this work. We start with a detailed analysis of transport properties of C60 molecular tunnel junction. We find that charge transport is mediated by resonances due to an alignment of the Fermi level of the electrodes and the lowest unoccupied C60 molecular orbital. We then make a first step toward the problem of analyzing phonon modes of the C60 by examining the rotational and the center-of-mass motions by calculating the total energy. We obtain the characteristic frequencies of the libration and the center-of-mass modes, the latter is quantitatively consistent with recent experimental measurements. Next, we developed a DFT-NEGF theory for the general purpose of calculating any vibrational modes in molecular tunnel junctions. We derive an analytical expression for dynamic matrix within the framework of DFT-NEGF. Diagonalizing the dynamic matrix we obtain the vibrational (phonon) spectrum of the device. Using this technique we calculate the vibrational spectrum of benzenedithiolate molecule in a tunnel junction and we investigate electron-phonon coupling under an applied bias voltage during current flow. We find that the electron-phonon coupling strength for this molecular device changes drastically as the bias voltage increases, due to dominant contributions from the center-of-mass vibrational modes of the molecule. Finally, we have investigated the reverse problem, namely the effect of molecular vibrations on the tunneling current. For this purpose we developed the DFT-NEGF-SCBA formalism, and an example is given illustrating the power of this formalism.
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Sica, G. "Electron-electron and electron-phonon interactions in strongly correlated systems." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12194.
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In this work we investigate some aspects of the physics of strongly correlated systems by taking into account both electron-electron and electron-phonon interactions as basic mechanisms for reproducing electronic correlations in real materials. The relevance of the electron-electron interactions is discussed in the first part of this thesis in the framework of a self-consistent theoretical approach, named Composite Operator Method (COM), which accounts for the relevant quasi-particle excitations in terms of a set of composite operators that appear as a result of the modification imposed by the interactions on the canonical electronic fields. We show that the COM allows the calculation of all the relevant Green s and correlation functions in terms of a number of unknown internal parameters to be determined self-consistently. Therefore, depending on the balance between unknown parameters and self-consistent equations, exact and approximate solutions can be obtained. By way of example, we discuss the application of the COM to the extended t-U-J-h model in the atomic limit, and to the two-dimensional single-band Hubbard model. In the former case, we show that the COM provides the exact solution of the model in one dimension. We study the effects of electronic correlations as responsible for the formation of a plethora of different charge and/or spin orderings. We report the phase diagram of the model, as well as a detailed analysis of both zero and finite temperature single-particle and thermodynamic properties. As far as the single-band Hubbard model is concerned, we illustrate an approximated self-consistent scheme based on the choice of a two-field basis. We report a detailed analysis of many unconventional features that arise in single-particle properties, thermodynamics and system's response functions. We emphasize that the accuracy of the COM in describing the effects of electronic correlations strongly relies on the choice of the basis, paving the way for possible multi-pole extensions to the two-field theory. To this purpose, we also study a three-field approach to the single-band Hubbard model, showing a significant step forward in the agreements with numerical data with respect to the two-pole results. The role of the electron-phonon interaction in the physics of strongly correlated systems is discussed in the second part of this thesis. We show that in highly polarizable lattices the competition between unscreened Coulomb and Fröhlich interactions results in a short-range polaronic exchange term Jp that favours the formation of local and light pairs of bosonic nature, named bipolarons, which condense with a critical temperature well in excess of hundred kelvins. These findings, discussed in the framework of the so-called polaronic t-Jp model, are further investigated in the presence of a finite on-site potential U, coming from the competition between on-site Coulomb and Fröhlich interactions. We discuss the role of U as the driving parameter for a small-to-large bipolaron transition, providing a possible explanation of the BEC-BCS crossover in terms of the properties of the bipolaronic ground state. Finally, we show that a hard-core bipolarons gas, studied as a charged Bose-Fermi mixture, allows for the description of many non Fermi liquid behaviours, allowing also for a microscopic explanation of pseudogap features in terms of a thermal-induced recombination of polarons and bipolarons, without any assumption on preexisting order or broken symmetries.
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Sica, Gerardo. "Electron-electron and electron-phonon interactions in strongly correlated systems." Doctoral thesis, Universita degli studi di Salerno, 2013. http://hdl.handle.net/10556/1418.
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2011 - 2012In this work we investigate some aspects of the physics of strongly correlated systems by taking into account both electron-electron and electron-phonon interactions as basic mechanisms for reproducing electronic correlations in real materials. The relevance of the electron-electron interactions is discussed in the first part of this thesis in the framework of a self-consistent theoretical approach, named Composite Operator Method (COM), which accounts for the relevant quasi-particle excitations in terms of a set of composite operators that appear as a result of the modification imposed by the interactions on the canonical electronic fields. We show that the COM allows the calculation of all the relevant Green’s and correlation functions in terms of a number of unknown internal parameters to be determined self-consistently. Therefore, depending on the balance between unknown parameters and self-consistent equations, exact and approximate solutions can be obtained. By way of example, we discuss the application of the COM to the extended t-U- J-h model in the atomic limit, and to the two-dimensional single-band Hubbard model. In the former case, we show that the COM provides the exact solution of the model in one dimension. We study the effects of electronic correlations as responsible for the formation of a plethora of different charge and/or spin orderings. We report the phase diagram of the model, as well as a detailed analysis of both zero and finite temperature single-particle and thermodynamic properties. As far as the single-band Hubbard model is concerned, we illustrate an approximated selfconsistent scheme based on the choice of a two-field basis. We report a detailed analysis of many unconventional features that arise in single-particle properties, thermodynamics and system’s response functions. We emphasize that the accuracy of the COM in describing the effects of electronic correlations strongly relies on the choice of the basis, paving the way for possible multi-pole extensions to the twofield theory. To this purpose, we also study a three-field approach to the single-band Hubbard model, showing a significant step forward in the agreements with numerical data with respect to the two-pole results. The role of the electron-phonon interaction in the physics of strongly correlated systems is discussed in the second part of this thesis. We show that in highly polarizable lattices the competition between unscreened Coulomb and Fröhlich interactions results in a short-range polaronic exchange term Jp that favours the formation of local and light pairs of bosonic nature, named bipolarons, which condense with a critical temperature well in excess of hundred kelvins. These findings, discussed in the framework of the so-called polaronic t-Jp model, are further investigated in the presence of a finite on-site potential ~U , coming from the competition between on-site Coulomb and Fröhlich interactions. We discuss the role of ~U as the driving parameter for a small-to-large bipolaron transition, providing a possible explanation of the BEC-BCS crossover in terms of the properties of the bipolaronic ground state. Finally, we show that a hard-core bipolarons gas, studied as a charged Bose-Fermi mixture, allows for the description of many non Fermi liquid behaviours, allowing also for a microscopic explanation of pseudogap features in terms of a thermal-induced recombination of polarons and bipolarons, without any assumption on preexisting order or broken symmetries. [edited by author]
XI n.s.
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Ren, Yan-Ru. "Orbital spin-splitting factors for conduction electrons in lead." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25961.
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A detailed experimental study has been made of the spin-splitting factors ℊc for magnetic Landau levels associated with conduction electrons in extremal orbits on the Fermi surface of lead. This information has been derived from the waveform of the de Haas-van Alphen (dHvA) quantum oscillations in the magnetization of single-crystal lead spheres at temperatures of about 1.2 K and with applied magnetic fields in the range 50-75 kG. A commercial spectrum analyzer has been used to provide on-line values of the harmonic amplitudes in the dHvA waveform, and the values of ℊc have been extracted from the relative strengths of the harmonics.
Serious systematic errors in ℊc can arise on account of waveform distortions caused by the small and subtle difference between the externally applied field H and the magnetizing field B acting on the conduction electrons. In 1981 Gold and Van Schyndel demonstrated that these 'magnetic-interaction' distortions could be suppressed to a large extent by using negative magnetic feedback to make the induction B within the sample be the same as H (or very nearly so). This thesis describes the first in-depth application of the magnetic-feedback technique to the systematic study of any metal. Particular attention has been paid to the effect of sample inhomogeneity, and Shoenberg's treatment of the magnetic interaction in a non-uniform sample has been generalized to include magnetic feedback. This theory accounts well for many features in the experimental data, especially those which remained a puzzle in the earlier work of Gold and Van Schyndel.
Experimental ℊc values are given for the first time for most of the extremal orbits on the lead Fermi surface and for high-symmetry directions of the magnetic field. Indeed these are the most detailed data reported for any polyvalent metal. The ℊc factors for the different orbits and field directions are found to span the range from 0.56 to 1.147. These large net deviations from the free-electron value ℊ₀ = 2.0023 are consequences of the strong spin-orbit and electron-phonon interactions, and an attempt has been made to separate these two contributions to the ℊ-shifts.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Chen, T. M. "Electron-electron interactions in GaAs quantum wires." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597526.
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The first experiment presents a novel method for continuously tracking the energies of the 1D subbands as a function of carrier density. I show a peculiar dc conductance feature in the region where the so-called 0.85(2e2/h) plateau in differential conductance is observed, directly demonstrating the pinning effect of the energy level of the minority spin-up electrons. A model concerning providing for non-linear population of the 1D subband with dc bias is proposed to explain the unusual differential conductance value of the 0.85(2e2/h) plateau. The second experiment shows that a fully spin-polarised current, consisting of a single spin-type only, can be created without external magnetic fields. When a source-drain bias lifts the momentum degeneracy, the dc measurements show that it is possible to achieve a unidirectional transport with a ferromagnetic order and this ordered spin array is destroyed once transport in both directions commences. The degree of spin polarisation of currents, between full spin polarisation, partial spin polarisation, and spin degeneracy, is thus simply controlled by source-drain bias and split-gate voltage, something of considerable value for spintronics. I then present four odd-even spin phenomena in the third experiment, showing clear evidence that a quasi-one-dimensional system tends to spontaneous spin polarisation with the energy band of minority spin-up electrons being reluctant to populate, thus widening the energy gap between two spin types. Variation of g-factor within a single subband is measured using a dc conductance technique, showing the g-factor oscillates as the 1D subbands are filled one by one with increasing carrier density. The last experiment introduces new experimental data of the zero-bias anomaly (ZBA), showing clear evidence that the ZBA observed in quantum wires in fact has a different origin from the Kondo effect seen in quantum dots. I propose a phenomenological model wherein the zero-bias anomaly in 1D quantum wires is in fact attributed to a upward shift of the 1D subband energy with source-drain bias.
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Pierre, Frédéric. "Interactions electron-electron dans les fils mesoscopiques." Paris 6, 2000. http://www.theses.fr/2000PA066375.
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Les interactions electron-electron limitent la coherence quantique des electrons dans les metaux et leur permettent d'atteindre l'equilibre thermique a basse temperature. Ces interactions sont faibles car les electrons dans les metaux sont etroitement ecrantes par la polarisation qu'ils induisent dans le milieu forme par les autres electrons. Dans le regime mesoscopique, on s'attend a ce que les chocs elastiques sur les defauts du reseau, les bords du metal et les impuretes diminuent l'efficacite de l'ecrantage et donc augmentent les interactions. L'objet de cette these est precisement de determiner experimentalement la nature des interactions inelastiques subies par les electrons a basse temperature dans les fils mesoscopiques. Dans la premiere partie, nous presentons la mesure du taux avec lequel les electrons echangent de l'energie dans des fils d'argent, de cuivre et d'or. Pour cela, nous mesurons la fonction de distribution en energie des electrons dans un regime stationnaire hors-equilibre. Dans la deuxieme partie, nous presentons la mesure du temps de coherence de phase des electrons en fonction de la temperature, egalement dans des fils de cuivre d'or et d'argent. La coherence quantique des electrons est limitee par toutes les collisions inelastiques independamment de l'energie echangee. Nous avons deduit le temps de coherence de phase de la mesure des corrections de localisation faible a la conductance des fils. Dans la troisieme partie, nous presentons des mesures de l'anomalie de conductance aux petites tensions d'une longue jonction tunnel entre un fil d'aluminium et un plan de masse. Cette depression de la conductance tunnel est un autre effet de l'interaction coulombienne. Pour comparer mesures et predictions theoriques, nous avons reformule les predictions du calcul microscopique des interactions entre electrons en terme d'impedance electromagnetique, dans un langage similaire a celui utilise par la theorie phenomenologique du blocage de coulomb.
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Phinney, Isabelle Y. "Probing electron-electron and electron-phonon interactions in twisted bilayer graphene." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127092.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 81-86).
Two-dimensional systems, and, most recently, moire systems, have risen to the forefront of condensed matter physics with the advent of experimental techniques that allow for controlled stacking of van der Waals heterostructures [17, 54]. For example, it was recently discovered that when two pieces of atomically thin carbon (graphene) are twisted at 1.1° with respect to one another, they display a variety of effects, including superconducting behavior [10]. Experimental investigation of the behavior of small-angle twisted bilayer graphene (SA-TBG) as a function of twist angle is imperative to understanding the mechanisms that play into the many interesting, strongly-interacting phenomena that the moire system displays. In this thesis, I present three experiments which explore electron-electron and electron-phonon interactions in SA-TBG. I first consider SA-TBG as a host for a viscous electron fluid and look for the onset of fluid behavior via electron transport. Then I investigate the temperature dependence of resistivity in SA-TBG devices at a number of angles. The final experiment examines magnetophonons in three devices above the magic angle and compares the findings to theoretical results.
by Isabelle Y. Phinney.
S.B.
S.B. Massachusetts Institute of Technology, Department of Physics
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Bassett, L. C. "Probing electron-electron interactions with a quantum antidot." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596454.
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In the integer quantum Hall (IQH) regime, an antidot provides a finite, controllable ‘edge’ of quantum Hall fluid which is an ideal laboratory for investigating the collective dynamics of large numbers of interacting electrons. Transport measurements of single antidotes probe the orbital energy spectra of the antidot edge, and gate-defined antidot devices offer the flexibility to vary both the dimensions of the antidot and the couplings to the extended IQH edge modes which serve as leads. We can also use the spin-selectivity of the IQH edge modes to perform spin-resolved transport measurements, from which we can infer the antidot spin-structure. This thesis describes a combination of such experimental measurements and related computational models designed to investigate the effects of electron-electron interactions in quantum antidotes, with general implications for the physics of spin and charge in IQH systems. Our work provides a powerful example of the practical applications of IQH edge modes for selective transport in mesoscopic quantum electronics, which we have used to perform the first spin-resolved measurements of VAD = 2 transmission resonances. Our discovery of spin-charge separation in the low-field antidot excitation spectrum paints a picture of the antidot as a finite droplet of interacting IQH fluid in the LLL, with all of the rich physics of exchange, collective modes, spin textures, etc., which this entails. Our results are therefore relevant not only for the physics of antidots, but more broadly for the understanding of interacting electronic systems of many particles in the IQH regime.
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Ung, Kim-Chau. "Effects of electron-electron and electron-phonon interactions in narrow-band systems." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186622.
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Different ordered states, CDW, BOW, and SDW, are investigated theoretically for both interacting and noninteracting cases as well as for different band filling systems. For noninteracting case, we find that the BOW is always accompanied by the CDW and vice versa in one-dimensional system for commensurability > 2. The strong electron-molecular vibration coupling drives both CDW and BOW, and plays thus an important role in the stabilization of the CDW state for these non-half-filled materials. Within the simply extended Peierls-Hubbard model, the experimentally observed lattice distortion of MEM(TCNQ)₂ can be precisely understood with our model calculation. In addition to the on-site repulsion U, the nearest-neighbor Coulomb interaction V is shown to play a vital role in the strongly correlated system; and a critical value V(c) is found for the quarter-filled system. With the understanding of the dominant broken symmetries in quasi-one-dimensional quarter-filled band, some implications for superconducting materials are discussed. The effect of band filling on the 4k(F) BOW instability is studied by the extended Peierls-Hubbard model; it is found that a strongly systematic tendency of the 4k(F) is dependent on the band filling. By studying the pair binding energy in some small clusters, we point out that the electron (or hole) pairing is not due to the Coulomb interaction, at least in the small U region.
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Zoccante, Paolo. "Electron-electron renormalization of the electron-phonon coupling in many-valley systems : the case of ZrNCl." Paris 6, 2013. http://www.theses.fr/2013PA066760.
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Lix ZrNCl is a layered superconductor with a double-honeycomb structure whose critical superconducting temperature (TC ) increases upon doping reduction. This is unexpected, since this system presents parabolic bands centered on the zone boundary K point, and a quasi-2D electron-gas structure with an almost constant density of states. As such, it can be considered the physical realization of a valley-degenerate electron gas. In the first part of this thesis, we present a theoretical investigation of the superconducting properties of Lix ZrNCl as a function of doping using Density Functional Theory. The computed vibrational spectra display a strong coupling in the reciprocal space region near the high-symmetry Γ and K special points. The predicted critical temperatures are in agreement with the experiments at high doping, but do not explain the low-doping TC enhancement. In the second part of the thesis, we establish an exact mapping between the electron-phonon Hamiltonian in a many-valley system and the Hamiltonian of an electron gas in a magnetic field. Quantum Monte Carlo fully-correlated calculations are used to correct the Density Functional theory results. We found that the inclusion of many-body effects leads to an enhancement of TC at low doping via a doping-dependent renormalization of the electron-phonon coupling. This enhancement depends strongly on the thickness of the electronic layer and the interactions with the neighbouring charged planes. Due to the fundamental nature of this mechanism, we expect to find the same low electron-density behavior in a wide class of many-valley layered materialsLix ZrNCl est un supraconducteur lamellaire; sa température critique supraconductrice (TC ) augmente lorsque la quantité de dopant dans le matériau est réduite. Ce comportement est inattendu, car le système présente des bandes paraboliques centrées sur les points spéciaux à haute symétrie K et une structure électronique quasi-2D, avec une densité d’états presque constante. Lix ZrNCl peut être considéré comme la réalisation physique d’un gaz d’électrons avec deux vallées dégénérées. Dans la première partie de cette thèse, nous étudions les propriétés supraconductrices en fonction du dopage de Lix ZrNCl en utilisant la Théorie de la Fonctionnelle de la Densité (DFT). Les spectres vibrationnels du système montrent un fort couplage dans la région proche de Γ et K. Les températures critiques calculées sont en accord avec les données expérimentales à haut dopage, mais n’expliquent pas la hausse de TC à bas dopage. Dans la deuxième partie de la thèse, on établit une correspondance exacte entre l’Hamiltonien électron-phonon d’un système à plusieurs vallées et l’Hamiltonien d’un gaz d’électrons dans un champ magnétique. Des calculs Monte Carlo Quantique sont utilisés pour corriger les résultats obtenus avec la DFT. L’inclusion des effets à N-corps provoque une hausse de la température critique à bas dopage, due à la renormalisation de l’interaction électron-phonon. Cette augmentation dépend fortement de l’épaisseur de la couche électronique et des interactions avec les autres plans chargés. À cause de la nature fondamentale de ce mécanisme, nous nous attendons à trouver un comportement similaire sur une grande gamme de matériaux présentant une dégénérescence de vallées
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Gardel, Emily Jeanette. "Microbe-electrode interactions: The chemico-physical environment and electron transfer." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11185.
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This thesis presents studies that examine microbial extracellular electron transfer that an emphasis characterizing how environmental conditions influence electron flux between microbes and a solid-phase electron donor or acceptor. I used bioelectrochemical systems (BESs), fluorescence and electron microscopy, chemical measurements, 16S rRNA analysis, and qRT-PCR to study these relationships among chemical, physical and biological parameters and processes.Engineering and Applied Sciences
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Moreira, Leandro Malard. "Raman spectroscopy of graphene:: probing phonons, electrons and electron-phonon interactions." Universidade Federal de Minas Gerais, 2009. http://hdl.handle.net/1843/ESCZ-7ZFGDY.
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Since the identification of mono and few graphene layers in a substrate in 2004, intensive work has been devoted to characterize this new material. In particular, Raman spectroscopy played an important role in unraveling the properties of graphene systems. Moreover resonant Raman scattering (RRS) in graphene systems was shown to be an important tool to probe phonons, electrons and electronphononinteractions. In this thesis, by using different laser excitation energies, we obtain important electronic and vibrational properties of mono- and bi-layer graphene. For monolayer graphene, we determine the phonon dispersion near the Dirac point for the in-plane transverse optical (iTO) mode and the in-plane longitudinal acoustic (iLA) mode. These results are compared with recent theoretical calculations for the phonon dispersion around the K point. For bilayer graphene we obtain the Slonczewski-Weiss-McClure band parameters. These results show that bilayer graphene has a strong electron-hole asymmetry, which is larger than in graphite. In a gating experiment, we observe that the change in Fermi level of bilayer graphene gives rise to a symmetry breaking, allowing the observation of both the symmetric (S) and anti- symmetric (AS) phonon modes. The dependence of the energy and damping of these phonons modes on the Fermi level position is explained in terms of distinct couplings of the S and AS phonons with intraand inter-band electron-hole transitions. Our experimental results confirm the theoretical predictions for the electron-phonon interactions in bilayer graphene. We also study the symmetry properties of electrons and phonons in graphene systems as a function of the number of layers, by a group theory approach. We derive the selection rules for the electron-radiation and for the electron-phonon interactions at all points in the Brillouin zone. By considering these selection rules, we address the double resonance Raman scattering process. The selection rules for monolayer and bilayer graphene in the presence of an applied electric field perpendicular to the sample plane are also discussed.Desde a identificação de uma ou poucas camadas de grafeno em um substrato em 2004, trabalhos intensivos tem sido feitos para se caracterizar esse novo material. Em particular, a Espectroscopia Raman Ressonante tem sido muito importante para elucidar propriedades físicas e químicas em sistemas de grafeno. A Espectroscopia Raman Ressonante também tem se mostrado como uma ferramenta importante para se estudar fônons, elétrons e interações elétron-fônon em grafeno. Nesta tese, ao usarmos diferentes energias de laser de excitação, nós obtivemos propriedades importantes sobre as estruturas eletrônicas e vibracionais para uma e duas camadas de grafeno. Para uma monocamada de grafeno, nós determinamos a dispersão de fônons perto do ponto de Dirac para o modo óptico transversal no plano (iTO) e para o modo acústico longitudinal no plano (iLA). Comparamos nossos resultados experimentais como cálculos teóricos recentes para a dispersao de fônons nas proximidades do ponto K. Para a bicamada de grafeno, nós obtivemos os parâmetros de estrutura eletrônica do modelo de Slonczewski-Weiss-McClure. Nossos resultados mostram que a bicamada de grafeno possue uma forte assimetria elétron-buraco, que por sua vez é mais forte que no grafite. Em experimentos aplicando uma tensão de porta, variamos o nível de Fermi em uma bicamada de grafeno, o que levou uma quebra de simetria, deixando assim ambos os modos de vibração simétricos (S) e anti-simétricos (AS) ativos em Raman. A dependência da energia e do amortecimento desses modos de fônons com a energia de Fermi é explicada através do acoplamento elétron-buraco intra- ou inter- banca. Nossos resultados experimentais deram suporte às previsões teóricas para interações elétron-fónon em uma bicamada de grafeno.
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Ozfidan, Asli Isil. "Electron-Electron Interactions in Optical Properties of Graphene Quantum Dots." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32857.
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In this thesis, I present a theory of electron-electron interactions in optical properties of graphene and transition metal dichalcogenides (TMDCs), two dimensional nanostructures with a hexagonal lattice.
We start our discussion with electron-electron interactions in artificial rings for which the strength of interactions can be varied and exact results can be obtained. The artificial rings are described by the extended Hubbard model and solved using an exact diagonalization method in real and Fourier space of configurations. Exact and analytical results for charged rings are obtained in the limit of very strong interactions. For the quadruple quantum dot ring and the artificial benzene ring, we find that chirality leads to the appearance of a topological phase and an effective gauge field that determines the ground state character with varied interaction strength. For the charged artificial benzene ring, our numerical results show a transition from a degenerate to a non-degenerate ground state with increasing strength of Coulomb interactions. We show that the artificial gauge and the transition in the ground state can be detected as changes in the optical absorption spectrum.
In the second part of the thesis, the electronic and optical properties of colloidal graphene quantum dots (CGQD) consisting of many benzene rings are determined. The CGQDs are described by the combination of tight binding, mean field Hartree Fock (HF) and Configuration Interaction methods. The single particle properties are described through the tight binding method based on the pz carbon orbitals. Screened Coulomb interactions between electrons, including direct, exchange, and scattering matrix elements, are calculated using Slater pz orbitals. HF ground states corresponding to semiconductor, Mott-insulator, and spin-polarized phases are obtained as a function of the strength of the screened interaction versus the tunnelling matrix element. The many-body ground and excited states in the semiconducting phase are constructed as a linear combination of a finite number of electron-hole pair excitations from the HF ground state (GS). The Hamiltonian is constructed in the subspace of multi-pair HF excitations to obtain the low energy, many body states by exact diagonalization using the Lanczos method.
The degeneracy of the valence- and conduction-band edges of 3-fold rotationally symmetric CGQDs is shown to lead to a characteristic exciton and bi-exciton spectrum. The low-energy exciton spectrum is predicted to consist of two bright-singlet exciton states corresponding to two circular polarizations of light and a lower-energy band of dark singlets and dark triplets. The robustness of the bright degenerate singlet pair against correlations in the many-body state is demonstrated as well as the breaking of the degeneracy by the lowering of symmetry of the CGQD.
Band edge biexciton energies and binding energies are predicted, and two degenerate exciton (X) states and a corresponding biexciton (XX) state are identified for the generation of an XX-X cascade. The Auger coupling of XX and excited X states is determined and our theoretical results are compared with experimental absorption and non-linear transient absorption spectra.
In the third and final part of the thesis, we replace the two non-equivalent carbon atoms of the graphene hexagonal lattice with a heavy transition-metal atom M, (e.g. Mo or W) and a dimer X2 (e.g. S). The bandstructure of a monolayer MX2 is calculated using density functional theory (DFT). It is shown that a direct gap opens up at all K points of the Brillouin zone and strong spin orbit coupling leads to spin splitting of the valence and conduction bands and emergence of valley dependent optical selection rules. Finally, the magnetoluminescence experiments on a monolayer WS2 emitting circularly polarized light upon its excitation by unpolarized light are described. The emission of polarized light in zero magnetic field is explained by the possibility of formation of a valley polarized 2D electron gas in unintentionally doped WS2.
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Szulakowska, Ludmila. "Electron-electron Interactions and Optical Properties of Two-dimensional Nanocrystals." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40983.
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This thesis presents a theory of electron-electron interaction effects and optical properties
of nanostructures of two-dimensional (2D) honeycomb crystals - graphene and transition metal dichalcogenides (TMDC). Graphene, a semimetallic hexagonal lattice of carbon atoms can be described by a massless Dirac fermion model, with the conduction band (CB) and valence band (VB) touching in the corners of a hexagonal Brillouin zone, valleys K and -K. TMDC crystals sites host either a transition metal atom or a chalcogen dimer, which opens the energy gap and allows for describing their low-energy nature with massive Dirac fermion (mDf) model. The metal atom in TMDC crystals causes strong spin-orbit (SO) coupling, resulting in large SO splitting in bands at both valleys. For TMDCs it is possible to excite carriers in each valley with oppositely circularly polarised light, which offers promising prospects for devices based on electrons valley index, i.e. valleytronic devices. Additionally, the optical response of TMDCs is enhanced by the presence of secondary CB minima, at Q-points.
The dimensionality of 2D crystals can be further reduced to form quantum dots (QDs) - nanostructures con ned in all dimensions. This thesis first discusses hexagonal graphene QDs, which exhibit energy gap oscillation as a function of size, due to the edge type: zigzag or armchair. These QDs are divided into concentric rings, analysed with tight-binding (TB) model. An armchair edged QD is built from a zigzag edged QD by adding a 1D Lieb lattice of carbon atoms on its edge. The energy gap is formed differently for both edges: from the outer ring states for zigzag edge and from the 1D Lieb lattice zero-energy states for armchair edge, which causes the energy gap. The remaining portion of the thesis focuses on TMDC materials. First a TB model is presented for a member of TMDC group, MoS2, using three d orbitals of Mo atom and three p orbitals of the S2 dimers. The tunneling matrix elements between nearest-neighbor and next-nearest-neighbour sites are explicitly derived at K and -K to form a six band TB Hamiltonian. Its solutions are fitted to the bands obtained from the density functional theory ab initio calculations to obtain the correct behaviour of bands around K and additional minima at Q-points, which explains the role of d orbitals in TMDCs. Close to K the TB model is reduced to mDf model, which
is then studied in response to light, yielding the valley-dependent selection rules for
absorption. The interaction of mDf with light is further studied in the presence of strong external magnetic eld, which leads to the formation of Landau levels (LLs), asymmetric
between both valleys, and valley Zeeman splitting. These LLs are populated with electrons
to form a Hartree-Fock ground state (GS), which can exhibit valley polarisation due to the LL asymmetry. Quasi-electron-hole excitations out of the GS are then formed and their self-energy, vertex corrections and scattering energy is calculated. The effect of electron-electron interactions on valley Zeeman splitting is demonstrated and the Bethe-Salpeter equation is numerically solved to give magnetoexciton spectrum for both valleys. The results include a valley-dependent absorption spectrum for mDf magnetoexcitons that vary with the valley polarisation.
The final part of this thesis discusses the single particle and interacting effects in gated MoS2 QDs. First, I perform a single electron atomistic calculation for a million-atom computational box with periodic boundary conditions based on a TB model developed from ab initio methods for bulk MoS2. Electrons are then con ned with a parabolic electrostatic potential from top metallic gates. They exhibit twofold degenerate harmonic oscillator energy spectrum with shell spacing ω associated with valleys K as well as a sixfold degenerate energy spectrum derived from the Q-points. The degeneracy of electronic shells is broken due to valley contrasting Berry curvature,which acts as an effective magnetic eld splitting opposite angular momentum states in both valleys. I populate up to ve K-derived harmonic oscillator shells with up to six electrons and turn on the electron-electron interactions. The resulting GS phases form two regimes dependent on ω, which are dominated each by a broken-symmetry phase, i.e. valley and spin polarised GS for low ω and valley and spin unpolarised but spin intervalley antiferromagnetic GS for higher ω. This behaviour is explained as an effect of the strong SO splitting, weak intervalley exchange interaction and strong correlations. Means of detecting these effects in experiment based on the spin and valley blockade are proposed. These results advance the understanding of interaction-driven breaking of symmetry for valley systems, crucial for designing of valleytronic devices in the future.
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Schultze, Martin. "Attosecond real time observation of ionization and electron-electron interactions." Diss., kostenfrei, 2008. http://edoc.ub.uni-muenchen.de/9509/.
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Schwab, Peter [Verfasser]. "Electron-Electron Interactions and Charge Transport in Mesoscopic Conductors / Peter Schwab." Augsburg : Universität Augsburg, 2007. http://d-nb.info/1077692536/34.
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Gee, Philip James. "Studies of electron-electron interactions in a system of reduced dimensionality." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360300.
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Kumar, Arvind Shankar Shankar. "Investigating Electron-Electron Interactions in 2D Semiconductor Systems through Quantum Transport." Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1624475904980951.
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Prada, Marta. "Electronic interactions in few electron quantum dot networks for memory storage applications." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418761.
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Grumbling, Emily Rose. "Electronic Structure, Intermolecular Interactions and Electron Emission Dynamics via Anion Photoelectron Imaging." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195933.
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This dissertation explores the use of anion photoelectron imaging to interrogate electronic dynamics in small chemical systems with an emphasis on photoelectron angular distributions. Experimental ion generation, mass selection, laser photodetachment and photoelectron imaging were performed in a negative-ion photoelectron imaging spectrometer described in detail. Results for photodetachment from the simplest anion, H⁻, are used to illustrate fundamental principles of quantum mechanics and provide basic insight into the physics behind photoelectron imaging from a pedagogical perspective. This perspective is expanded by introducing imaging results for additional, representative atomic and small molecular anions (O⁻, NH₂⁻ and N₃⁻) obtained at multiple photon energies to address the energy-dependence of photoelectron angular distributions both conceptually and semi-quantitatively in terms of interfering partial photoelectron waves. The effect of solvation on several of these species (H⁻, O⁻, and NH₂⁻) is addressed in photoelectron imaging of several series of cluster anions. The 532 and 355 nm energy spectra for H⁻(NH₃)n and NH₂⁻(NH₃)n (n = 0-5) reveal that these species are accurately described as the core anion solute stabilized electrostatically by n loosely coordinated NH3 molecules. The photoelectron angular distributions for solvated H⁻ deviate strongly from those predicted for unsolvated H⁻ as the electron kinetic energy approaches zero, indicating a shift in the partial-wave balance consistent with both solvation-induced perturbation (and symmetry-breaking) of the H⁻ parent orbital and photoelectron-solvent scattering. The photoelectron energy spectra obtained for the cluster series [O(N₂O)n]⁻ and [NO(N₂O)n]⁻ indicate the presence of multiple structural isomers of the anion cores, the former displaying sharp core-switching at n = 4, the latter isomer coexistence over the entire range studied. The photoelectron angular distributions for detachment from the O⁻(N₂O)n and NO⁻(N₂O)n isomers deviate strongly from those expected for bare O⁻ and NO⁻, respectively, in the region of an anionic shape resonance of N₂O, suggesting resonant photoelectron-solvent scattering. Partial-wave models for two-centered photoelectron interference in photodetachment from dissociating I₂⁻ is presented and discussed in the context of previous results. New time-resolved photoelectron imaging results for I₂⁻, for both parallel and perpendicular pump and probe beam polarizations, are presented and briefly discussed. Finally, new ideas and directions are proposed.
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Knoop, Steven. "Electron dynamics in ion-atom interactions." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2006. http://irs.ub.rug.nl/ppn/292151632.
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Monckton, Rhiannon. "Low energy electron interactions with water." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/low-energy-electron-interactions-with-water(c807bd78-59e3-4570-be3c-34feafc01fdf).html.
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Understanding the radiation chemistry of water is important in many disciplines including the nuclear industry, astrochemistry, and medicine. In recent years, low-energy electrons have been paid much greater attention, due to their abundance and reactivity in irradiated materials. Electrons with energies < 20 eV may interact via the dissociative electron attachment (DEA) mechanism, which has been found to cause single-strand breaks in DNA.DEA in water involves the capture of a low energy electron by a neutral water molecule into an outer orbital and is generally accompanied by excitation of the H2O molecule, causing it to dissociate. The aim of this work is to study the OH radical produced in DEA to H2O using laser-induced fluorescence (LIF).A high-vacuum chamber equipped with low energy electron gun, molecular beam and laser system was built for gas-phase studies of DEA in water. LIF spectra were recorded from OH formed by dissociation of gas-phase H2O, for determination of the rotational and vibrational state distributions. In addition to the gas-phase studies, low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices were investigated using a combination of temperature-programmed desorption (TPD) and infrared reflection-absorption spectroscopy (IRAS).For CO trapped within approximately 50 mono-layers of the vacuum interface both reduction and oxidation products were observed including HCO, H2CO, H3CO and CH3OH, and CO2. Concentration profiles of CO versus film thickness showed two zones in the film: a near-surface zone of preferential oxidation, and a zone of preferential reduction deeper in the film. A Monte Carlo model was developed based on diffusion of H atoms through the ice lattice, which supported the experimental results.
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Jura, Michael Pemberton. "Imaging electron flow, interference, and interactions in high-mobility two-dimensional electron gases /." May be available electronically:, 2009. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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De, Vega Esteban Sandra. "Plasmon-electron interactions in low dimensional materials." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/668847.
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Ever since the advent of modern technology, major developments have come hand in hand with miniaturization and speed of operation. A proof of this is provided by the impressive success of Moore's law, which predicted that the number of transistors per affordable microprocessor would double every two years. That would not have been possible if transistors kept their initial physical dimensions. By the end of 2018, MIT and University of Colorado researchers broke a new record for the smallest 3D transistor yet with a lateral size of only 2.5 nm. As of 2019, there are commercially available 5 nm transistors. Considering these sizes it is then remarkably important to understand and to be able to manipulate materials at the nanoscale, where they behave differently compared with macroscopic structures.
Hence, researchers have put substantial efforts towards finding the explanation of diverse phenomena at the nanoscale, engineering new nanodevices, and proposing or predicting new mechanisms to achieve the next generation of chips and integrated circuits. Indeed, the rise of the so-called low dimensional materials (graphene, transition metal dichalcogenides, cuprates, hBN, black P, carbon nanotubes, and others), i.e., those whose atomic planes are bonded by weak van der Waals forces (2D) or whose atoms are arranged in chains or tubes (1D), has been influenced by the quest for new more efficient and compact designs. In this thesis we study the optical properties of some of these materials and how they are modified by the interaction with electrons that, depending on the specific case, we consider to be either dopants, or impinging in highly-focused beams, or via tunneling.
Specifically, we start with a comprehensive analysis of plasmons, the collective oscillations of free electrons coupled to light, in finite highly-doped carbon nanotubes. Next, we explore how to select the proper plasmon mode excited by electron beams depending on the orientation and position of the latter and also how to improve the interaction between two quantum emitters when mediated by the main plasmonic mode in our structures. We predict record-high Purcell factors of the order of 10^8, which supports the use of carbon nanotubes as active plasmonic elements with high potential in optoelectronics and quantum optics.
We then continue with one dimensional systems, but now focusing on atomic chains to emulate simple solid-like structures where to inspect strong-field driven electron dynamics in solids. Specially, we tackle several still pending questions about the role of electron-electron interactions and the proper choice of material to achieve better high-harmonic generation yields. After that, we test these findings in more realistic 1D systems: carbon nanotubes. Eventually, we find that the addition of a small number of doping charges to semiconductors can enable intraband plasmon excitations that concentrate the impinging light and boosts the high-harmonic generation efficiency.
Next, we investigate how to use two dimensional heterostructures (stacked layers) for new compact ways of generating plasmons that do not need external light sources. More precisely, we propose tunneling electrons as plasmon triggers. We thus design a device consisting of a 1 nm-thick sandwich of graphene-hBN-graphene whose activation mechanism would be by an electron that tunnels from one graphene layer to another losing energy in the process that is invested into exciting plasmons. We predict a generation efficiency that can reach one plasmon per tunneled electron and that is robust upon distortions and variations in doping. We then complete this study by analyzing graphene-insulator-metal structures, which unfortunately present less efficient generation rate.
In summary, the outcomes of this thesis open new paths towards a more efficient generation of nonlinear processes in solid nanoarchitectures and optics-free manipulation at the nanoscale for future optoelectronic devices.Desde el advenimiento de la tecnología moderna, muchos desarrollos científicos han venido de la mano con la miniaturización y la velocidad. Una prueba de esto es el éxito de la Ley de Moore que predijo que el número de transistores por procesador se doblaría cada dos años y que no habría sido posible si los transistores hubiesen mantenido su tamaño original. A finales de 2018 investigadores del MIT y de la Universidad de Colorado batieron un nuevo récord del transistor más pequeño hasta la fecha de solo 2.5 nm de tamaño. En lo que a 2019 se refiere, ya hay transistores de 5 nm disponibles en el mercado. Considerando estas dimensiones, es de vital importancia tanto entender como poder manipular los materiales en la nanoescala, donde se compartan de una manera totalmente diferente a cómo lo hacen macroscópicamente. Así pues, los investigadores han puesto especial empeño en explicar diversos fenómenos en la nanoescala, en diseñar nuevos nanodispositivos y en proponer o predecir nuevos mecanismos para lograr las nuevas generaciones de chips y circuitos integrados. De hecho, el ascenso de los materiales de baja dimensionalidad (grafeno, TMDs, hBN, P negro y otros), i.e., con planos atómicos están enlazados por fuerzas de van der Waals (2D) o cuyos átomos se ordenan en cadenas o tubos (1D), ha venido por la constante búsqueda de nuevos diseños más compactos y eficientes. En esta tesis, estudiamos las propiedades ópticas de algunos de estos materiales y cómo se modifican debido a la interacción con electrones que, dependiendo del caso concreto, son dopantes o inciden en haces de electrones altamente focalizados. Más en particular, empezamos con un análisis de plasmones, la oscilación colectiva de electrones acoplada a la luz, en nanotubos de carbono (CNTs) finitos altamente dopados. A continuación, exploramos cómo seleccionar el modo del plasmón adecuado usando haces de electrones además de cómo mejorar la interacción entre dos emisores cuánticos cuando el modo plasmónico principal hace de mediador. Predecimos un valor de 10^8 para el factor de Purcell que respalda el uso de CNTs como elementos plasmónicos activos de gran potencial en optoelectrónica y óptica cuántica. Continuamos con sistemas unidimesionales pero esta vez eligiendo cadenas atómicas para emular estructuras sólidas simples donde examinar la dinámica de los electrones cuando están guiados por campos fuertes. Más concretamente, abordamos las cuestiones aún pendientes sobre el papel que juegan las interacciones electrón-electrón y la elección apropiada de material para la generación más eficiente de armónicos altos, y comprobamos nuestras conclusiones en sistemas 1D más realistas: los nanotubos de carbono. Así pues, encontramos que la adición de una pequeña cantidad de carga puede producir excitación de plasmones intrabanda que concentran el campo incidente y fomentan la eficiencia de la generación de armónicos altos. Después, investigamos cómo emplear heteroestructuras 2D para desarrollar nuevas formas más compactas de generar plasmones sin tener que utilizar fuentes externas, por ello utilizamos electrones de efecto túnel. El dispositivo que planteamos es un sándwich de grafeno-hBN-grafeno que se activaría por medio de un electrón que salta de una lámina de grafeno a la otra por efecto túnel, en el proceso pierde energía y ésta se invierte en excitar plasmones. Predecimos una eficiencia de generación que puede alcanzar un plasmón por electrón que salta por efecto túnel y que se mantiene a pesar de las posibles distorsiones por rotación de las láminas o de los cambios en el dopado. Además, completamos este estudio analizando el caso para estructuras de grafeno-aislante-metal y comprobamos que son menos eficientes que sus homólogas de grafeno-hBN-grafeno. En resumen, estos resultados abren la puerta hacia la generación de armónicos más eficiente en nanosólidos y hacia la manipulación en la nanoescala sin elementos ópticos para futuros nanodispositivos optoelectrónicos.
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Löfgren, Torbjörn. "Numerical modeling of electron beam-plasma interactions." Doctoral thesis, KTH, Alfvén Laboratory, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2878.
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Malton, S. P. "Laser interactions with high brightness electron beams." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1444964/.
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The International Linear Collider will be a high-precision machine to study the next energy frontier in particle physics. At the TeV energy scale, the ILC is expected to deliver luminosities in excess of 1034 cni" 2s_1. In order to achieve this, beam conditions must be monitored throughout the machine. Measurment of the beam emittance is essential to ensuring that the high luminosity can be provided at the interaction point. At the de sign beam sizes in the ILC beam delivery system, the Laserwire provides a non-invasive real-time method of measuring the emittance by the method of inverse Compton scattering. The prototype Laserwire at the PETRA stor age ring has produced consistent results with measured beam sizes of below 100 /nn. The Energy Recovery Linac Prototype (ERLP) is a technology testbed for the 4th Generation Light Source (4GLS). Inverse Compton scattering can be used in the ERLP as a proof of concept for a proposed 4GLS upgrade, and to produce soft X-rays for condensed matter experiments. The design constraints for the main running mode of the ERLP differ from those required for inverse Compton scattering. Suitable modifications to the optical lattice have been developed under the constraint that no new magnetic structures may be introduced, and the resulting photon distributions are described.
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Leadley, David Romwald. "Electron-phonon interactions in low dimensional structures." Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:3e8fe3de-4c61-48ac-a475-050b76901a6f.
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Transport properties of the two-dimensional electron gas (2DEG) in high magnetic fields are used to investigate scattering processes affecting the resistivity of GaAs-GaAlAs and GaInAs-InP heterojunctions and quantum wells: especially coupling of electrons to acoustic and optic phonons; and transitions between electric subbands. The experiments fall into two groups: A systematic study of magnetophonon resonance (MPR) between 30K and 300K. Resonance positions indicate a coupling substantially below the LO phonon energy, expected from 3D measurements. GaAs-GaAlAs hetero junctions show amplitudes varying smoothly with electron density (ns) and closely related to the 4K mobility. On rotation in magnetic field they decrease rapidly as the resonance position returns to the LO value. In modulation doped structures the damping factor is determined by remote impurity scattering. As ns is increased in GaInAs-InP the coupling frequency decreases dramatically from the GaAs-like LO at 272cm-1 to the InAs-like TO at 226cm-1. At higher electric fields the 'normal' MPR maxima invert, starting at low magnetic fields, to form 'hot electron' MPR minima, with maximum amplitude at ~60K. This is the first direct observation of HEMPR in 2D and is explained in a diffusion picture. At lower electric fields, additional resonances are identified with resonant cooling by inter-subband scattering. Comparisons are made with calculations and explanations sought including consideration of interface phonons; coupled plasmon-phonon modes; and shifts of the resonance positions due to the shape of the density of states. Low temperature magnetoresistance measurements in GaAs-GaAlAs heterojunctions with more than one occupied electric subband. Shubnikov-de Haas oscillations in perpendicular magnetic fields contain non-additive terms at electron temperatures > 2K where acoustic phonon mediated inter-subband scattering is comparable to intra-subband scattering. Subband separations and greatly enhanced g-factors [largest for electrons in the upper subband ] are deduced from the oscillations. Damping of the oscillations in field, gives values for quantum lifetimes (τs), much smaller than τtʼ, deduced from mobility. With two subbands occupied τs is always largest for the upper subband, while relative sizes of τt depend on sample quality. Study of electron energy loss rates, from thermal damping of the oscillations, shows enhancement in the region kTe ~ ħωcʼ, which is evidence for cyclotron phonon emission. Depopulating subbands in parallel fields causes the resistance to drop, by up to 60%, due to suppression of inter-subband scattering. Systematic studies show this scattering rate is independent of ns.
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Montgomery, M. J. "Ineleastic electron-phonon interactions in atomic wires." Thesis, Queen's University Belfast, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411758.
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McKenna, Paul. "Electron and laser interactions with positive ions." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326350.
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Siak, Selina Chin Yoke. "Localisation and interactions in disordered electron systems." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292495.
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Rosser, David M. "Effects of Strain, Electron-Electron Interactions, and Spin-Orbit Coupling in Honeycomb Layered Materials." Thesis, California State University, Long Beach, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10598952.
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Electronic transport and angle-resolved photoemission spectroscopy (ARPES) measurements were conducted on two different layered, honeycomb materials: graphene and sodium iridate (Na2IrO3). Graphene, the first two dimensional crystal observed in a laboratory, offers a system to explore novel quantum critical states theoretically predicted under the application of strain. Uniaxial strain was studied in suspended graphene using a microelectromechanical system (MEMS) via electronic transport. Strain was investigated as well by intercalation of C60 at the graphene-substrate (SiC) interface via ARPES. Sodium iridate is a relativistic Mott insulator proximate to the Kitaev model with unconventional electronic structure. An in-gap metallic feature was observed in ARPES measurements of Na2IrO3. Complementary evidence of a metallic conduction channel was observed in electronic transport measurements.
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Burmistrov, Igor. "[Theta] renormalization, superuniversality, and electron-electron interactions in the theory of the quantum Hall effect." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2006. http://dare.uva.nl/document/23446.
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Dash, Louise Karenza. "Electron-electron interactions and correlations in atomic scale wires : Luttinger liquids and their spectral signatures." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269623.
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Bruch, Anton [Verfasser]. "Operating machines at the nanoscale : Effects of electron-electron interactions and strong system-bath coupling on the working principles of electronic nanomachines / Anton Bruch." Berlin : Freie Universität Berlin, 2018. http://d-nb.info/1150704586/34.
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Howrigan, Shaun. "Electron-photon interactions in quantum dots, coupled oscillators." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/MQ33388.pdf.
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Khan, Anuja. "Solution structure and interactions of electron transfer proteins." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415724.
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Hardikar, Rahul Padmakar. "Dynamic electron-phonon interactions in one-dimensional models." Diss., Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-11092007-143010.
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Hagelberg, Frank. "Electron Dynamics in Molecular Interactions: Principles and Applications." Digital Commons @ East Tennessee State University, 2014. http://amzn.com/1848164874.
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This volume provides a comprehensive introduction to the theory of electronic motion in molecular processes an increasingly relevant and rapidly expanding segment of molecular quantum dynamics. Emphasis is placed on describing and interpreting transitions between electronic states in molecules as they occur typically in cases of reactive scattering between molecules, photoexcitation or nonadiabatic coupling between electronic and nuclear degrees of freedom.
Electron Dynamics in Molecular Interactions aims at a synoptic presentation of some very recent theoretical efforts to solve the electronic problem in quantum molecular dynamics, contrasting them with more traditional schemes. The presented models are derived from their roots in basic quantum theory, their interrelations are discussed, and their characteristic applications to concrete chemical systems are outlined. This volume also includes an assessment of the present status of electron dynamics and a report on novel developments to meet the current challenges in the field.
Further, this monograph responds to a need for a systematic comparative treatise on nonadiabatic theories of quantum molecular dynamics, which are of considerably higher complexity than the more traditional adiabatic approaches and are steadily gaining in importance. This volume addresses a broad readership ranging from physics or chemistry graduate students to specialists in the field of theoretical quantum dynamics.https://dc.etsu.edu/etsu_books/1055/thumbnail.jpg
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Caldwell, Joshua D. "Investigation of electron-nuclear spin interactions in two-dimensional electron systems via magnetoresistively detected magnetic resonance." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008397.
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Spark, Stephen N. "Pulsed mm-wave electron cyclotron maser experiments." Thesis, University of Strathclyde, 1988. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21311.
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A pulsed Electron Cyclotron Maser (E. C. M.) was developed and used to generate high power mm-waves in the W-band (75-110GHz) and the G-band (150-220GHz) frequency ranges. The relativistic electron beam (R. E. B.) was produced from a field-immersed, field-emission, cold cathode. A shaped anode cavity was designed for the optimum cavity Q, resonant frequencies, relative mode density, reflection coefficients and mode conversion in the output coupler. Two pulsed conventional field coils were used; coil#1 (maximum B-field : 9T) produced the uniform intra-cavity magnetic field and coil#2 (maximum B-field : 1T) acted as a cathode field tuning coil. The addition of the cathode tuning coil increased the useful output energy in any pulse by a factor of =400. Four diagnostics were used to determine the characteristics of the maser; 1) direct uncalibrated power monitoring, 2) calibrated frequency measurements (made using a quasi-optical diffraction grating spectrometer), 3) near field radiation pattern measurements and 4) calibrated absolute power measurements (made using a thermopile calorimeter). The following characteristics of the maser oscillation were identified: in the W-band, single mode oscillation in the TE03 mode was observed, centred at 95.2GHz, with an output power of =50kW. The cavity was crudely step-tunable with the excitation of the TE13 mode at 81.4GHz and the TE12 mode at 88.OGHz. In the G-band, multi-mode oscillation was observed at all values of the intra-cavity magnetic field. With the increased mode density at these frequencies, the maser was quasi-continuously tunable and 200GHz oscillation was observed. These results proved to be self-consistent with the device-dependent calculations used to design the system and the general E. C. M. theory developed previously.
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Napier, Stuart A. "Electron correlation and spin-dependent effects in the electron impact excitation of zinc atoms." University of Western Australia. School of Physics, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0098.
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[Truncated abstract] This work investigated electron correlation and spin-dependent effects in electron scattering from zinc for incident electron energies from the lowest excitation threshold at 4.003 eV to 50 eV. Experiments were performed using a crossed-beams electron impact spectrometer, which included an unpolarised electron gun, and also a spin-polarised electron gun. The apparatus was tested, and shown to be operating well, by repeating past studies of electron scattering from helium and argon. Emission cross sections for the 4s4p 3P1, 4s4p 1P1, 4s5s 3S1, 4s4d; 5d; 6d 3D1;2;3 and 4s4d; 5d 1D2 states were measured from the respective thresholds to 50 eV. These were compared with Convergent Close-Coupling (CCC) and B-spline R-matrix (BSRM) calculations of the 4s4p 3P1, 4s4p 1P1, 4s5s 3S1, 4s4d 1D2 and 4s4d 3D1;2;3 emission cross sections. There are serious discrepancies between the theories, and between the theories and experiment, which indicates strong continuum coupling and innershell excitation effects in the electron excitation of zinc. The differential elastic scattering signal at scattering angles of 30 , 54 , 90 and 110 was measured for incident electron energies from just below the lowest excitation threshold at 4.003 eV, to the ionisation threshold at 9.394 eV. Some assignments given by Sullivan et al [1] and Zatsarinny and Bartschat [2] were confirmed by the present experiment. An area of disagreement in the literature concerning the nature of a feature observed at the 4s4p 1P1 threshold at 5.796 eV was resolved in favour of Zatsarinny and Bartschat, who assign the feature as a cusp. ... Below the ionisation threshold, the 4s4p 3P1 photon excitation function supports the assignment of the near-4s4p 1P1 threshold feature as a cusp. Some of the overlapping negative-ion resonances which were observed near 7.5 eV in the 4s4p 3P1, 4s4p 1P1 and 4s5s 3S1 photon excitation functions were assigned with the assistance of the BSRM calculations of Zatsarinny and Bartschat. However, continuum coupling effects above 8 eV seem to cause the theoretical negative-ion resonance predictions to break down. Above the ionisation threshold, the near-11 eV negative-ion resonance effects depend on the configuration n, L and S of the neutral state excitation observed. This may be due to the properties of the mixed negative ion component states. Postcollision interaction (PCI) effects the 4s5s 3S1, 4s4d; 5d; 6d 3D1;2;3 and 4s4d; 5d 1D2 photon excitation functions. The PCI mechanism can populate the 4s4d; 5d; 6d 3D1;2;3 and 4s4d; 5d 1D2 states because the scattered and ejected electrons have a similar energy, and can thus exchange a large amount of orbital angular momentum. The present work demonstrates that electron correlation effects, especially those associated with innershell excitation, are very significant in electron scattering from zinc. Existing theoretical models of electron scattering from zinc inadequately treat electron correlations, and as a result of this are inaccurate, as shown here. The studies presented here should guide the development of models that accurately describe the innershell excitation effects, which are important for zinc and a great many other atoms.
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Yang, Xiaodong. "Effects of Electron-Phonon Interaction in Metals." Diss., Temple University Libraries, 2010. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/83903.
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PhysicsPh.D.
Phonons and electrons are two types of excitations which are responsible for many properties of condensed matter materials. The interaction between them plays an important role in condensed matter physics. In this thesis we present some theoretical investigations of the effects due to the interactions between phonons and electrons interactions. We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high magnetic fields. The effect of the magnetic field is considered unusual, as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical frame-work which can be used to describe the effect of a magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant. The temperature-dependence of the phonon spectrum of alpha-uranium has recently been measured by Manley et al. using inelastic neutron scattering and x-ray scattering techniques. Although there is scant evidence of anharmonic interactions, the phonons were reported to show some softening of the optic modes at the zone boundary. The same group of authors later reported that an extra vibrational mode was observed to form at a temperature above 450 K. The existence of the proposed new mode is inconsistent with the usual theory of harmonic phonons, as applied to a structure composed of a monoclinic Bravais lattice with a two-atom basis. We investigate the effect that the f electron-phonon interaction has on the phonon spectrum and its role on the possible formation of a breathing mode of mixed electronic and phonon character. We examine the model by using Green’s function techniques to obtain the phonon spectral density. Some materials undergo phase transitions from a high temperature state with periodic translational invariance to a state in which the electronic charge density is modulated periodically. The wave vector of the modulation may be either commensurate or incommensurate with the reciprocal lattice vectors of the high temperature structure. In the case of an incommensurate charge density wave, the system supports phason excitation. For an incommensurate state, the new ground state has a lower symmetry than the high temperature state since the charge density does not have long-ranged periodic translational order. If the metal is ideal (with no impurities), a charge density wave should be able to slide throughout the crystal without resistance, resulting in current flow similar to that of a superconductor. The phason is an excitation of the charge density wave which is related to the collective motion of electrons. We estimate the phason density of states, and the phason contribution to the specific heat. Angle-resolved photoemission experiments have been performed on USb2, and very narrow quasiparticle peaks have been observed in a band which local spin-density approximation (LSDA) predicts to osculate the Fermi energy. The observed band is found to be depressed by 17 meV below the Fermi energy. The experimentally observed quasiparticle dispersion relation for this band exhibits a kink at an energy of about 23 meV below the Fermi energy. The kink is not found in LSDA calculations and, therefore, is attributable to a change in the quasiparticle mass renormalization by a factor of approximately 2. The existence of a kink in the quasiparticle dispersion relation of a band which does not cross the Fermi energy is unprecedented. The kink in the quasiparticle dispersion relation is attributed to the effect of the interband self-energy involving transitions from the osculating band into a band that does cross the Fermi energy.
Temple University--Theses
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Stano, Peter. "Controlling electron quantum dot qubits by spin-orbit interactions." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983802254.
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Kiefer, Daniel. "Relativistic electron mirrors from high intensity laser nanofoil interactions." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-153796.
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Dean, M. P. M. "Superconductivity and electron-phonon interactions in graphite intercalation compounds." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598476.
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Systematic Raman scattering experiments were performed to compare the phonon properties in series of GICs BaC6, SrC6, YbC6 and CaC6. The key difference induced by changing the ions in this order is a reduction in the separation of the graphene layers, which is concurrent with an increase in the superconducting transition temperature Tc from < 80 mK to 11.5 K. It was possible to correlate the increase in Tc with a softening of an out-of-plane carbon related phonon, which was explained in terms of increased charge in the carbon-related electronic band. This provides evidence that the carbon-related phonons and electronic-bands are crucial to the superconductivity in these compounds. An in-plane carbon phonon was also measured, which was shown not to follow the Born-Oppenheimer approximation. Recent theoretical attempts to explain these effects cannot fully account for the observed electron-phonon scattering rate. Neutron scattering was also used to measure the high energy carbon-related phonons in CaC6. Due to the highly textured nature of the samples, special analytical techniques were developed to allow for the comparison between experiment and density functional theory (DFT). Overall, a good level of agreement between experiment and theory is found, which is significant in light of several other measurements of phonon related properties of CaC6, which disagree with the theoretical predictions. YbC6 was studied as a function of pressure to investigate the changes induced by reducing the layer separation. Tc initially increases consistent with the idea that moving the graphene layers closer increases Tc, however, at higher pressures Tc decreases disappearing at 7 GPa. These effects are discussed in light of a possible valence transition in YbC6.
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Stanton, Nicola Marie. "Experimental studies of electron-phonon interactions in gallium nitride." Thesis, University of Nottingham, 2001. http://eprints.nottingham.ac.uk/14212/.
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This thesis presents an experimental investigation of the electron-phonon interaction in GaN. Bulk epilayers, grown by MBE, and AIGaN/GaN heterostructures, grown by MOCVD, have been studied. The energy relaxation rate for hot electrons has been measured over a wide range of temperatures, allowing both acoustic and optic phonon emission to be studied in GaN epilayers. Direct phonon measurements, both studying the emission and absorption processes, have been performed. Detection of phonons emitted when hot electrons relax their excess energy complements the measurements of relaxation rates. Absorption of acoustic phonons by the epilayers, using both fixed and extended metal film phonon sources, allowed investigation into the effectiveness of the 2kF cutoff in the low mobility layers. The experimental findings are compared with the predictions of theory. AIGaN/GaN heterostructures were characterised and measurements of the energy relaxation rate in the temperature range 4K-40K obtained. Excellent agreement with theory is observed. A preliminary study of phonon absorption by the 2DEG system is presented, which allowed experimental determination of the "thickness" of the 2DEG and demonstrated the applicability of the technique in the study of low dimensional systems.
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Cox, Jonathan Mark. "Interactions of the electron transport proteins of methylotrophic bacteria." Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316489.
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Pursehouse, James. "Electron and photon interactions in magnesium, calcium and rubidium." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/electron-and-photon-interactions-in-magnesium-calcium-and-rubidium(cf98e2a6-ae7d-45b9-91c4-33f148a5678e).html.
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In the experiments detailed in this thesis, a series of scattering experiments were conducted in a versatile scattering chamber. In order to conduct these experiments, various electronic equipment was designed and built, including new computer controlled electron analyser power supplies. This new equipment was tested, adopted in this work, and is described in this thesis. The superelastic scattering technique was used on magnesium atoms to obtain a set of atomic collision parameters (ACPs), which describe the interaction. This was achieved by exciting a beam of magnesium atoms to the 3(1)P(1) excited state using resonant laser radiation around 285 nm, and using an electron beam with well defined momentum to de-excite the atoms. The momentum of the outgoing electrons was measured as the polarisation and scattering angle were varied, to obtain the ACPs. These measurements were carried out over an angular range of 30 degrees to 120 degrees and with incident energies equivalent to 35 eV, 40 eV, 45 eV, and 55 eV. A set of theoretical data was compared to the experimental results and found to be reasonably accurate at describing the interaction. Laser-aligned and ground-state (e,2e) ionisation measurements were taken from the 4(1)S(0) and 4(1)P(1) states of calcium. The measurements were taken with the energy of the scattered and ejected electrons set at 30 eV, and with one outgoing electron angle set to 45 degrees. The differential cross section was determined for a range of angles of the second electron, ranging from 30 degrees to 65 degrees. The incident and outgoing electron momenta were all defined in the same plane with the laser polarisation being in a plane perpendicular to the incident electron. The laser aligned (e,2e) measurements were compared to two theoretical models, one of which (a 3DW model) predicted an identically zero cross section when the laser polarisation was perpendicular to the scattering plane. The other model (a TDCC model) predicted a non-zero cross section, in agreement with the experiment. Simultaneous time-resolved two-colour photoionisation from the 5(2)P(3/2) and 6(2)P(3/2) states of rubidium was also conducted. These experiments investigated two pathways to creating 0.36 eV photoelectrons from rubidium. Photoelectrons were produced by either using laser radiation at ~780 nm to resonantly excite atoms to the 5(2)P(3/2) state followed by laser radiation at ~420 nm to ionise the atoms, or laser radiation at ~420 nm was used to resonantly excite atoms to the 6(2)P(3/2) state followed by radiation at ~780 nm which then ionised the atoms. Ionisation differential cross sections were measured over a full 360 degrees by rotating the laser polarisation vectors. By selectively detuning the laser beam so as to select individual ionisation pathways, and then by tuning both lasers to resonance, quantum interferences between the pathways that lead to ionisation were observed.
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Khalafalla, Mohammed Alshaikh Hamid. "Electron transport in nanocrystalline silicon : electrostatic and wavefunction interactions." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616240.
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