Tesis sobre el tema "Disordered electron systems"
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Nahm, In Hyun. "Two dimensional disordered electron systems". Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330179.
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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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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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Arnold, Wolfram Till. "Theory of electron localization in disordered systems /". view abstract or download file of text, 2000. http://wwwlib.umi.com/cr/uoregon/fullcit?p9986736.
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Thesis (Ph. D.)--University of Oregon, 2000.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 199-204). Also available for download via the World Wide Web; free to UO users.
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Kearney, Michael John. "Electron transport in low dimensional disordered systems". Thesis, University of Warwick, 1988. http://wrap.warwick.ac.uk/91877/.
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The transport properties of low dimensional systems (especially wires) are investigated when the dominant scattering is due to the impurities and is elastic. Such a situation is expected to be relevant to experiments carried out at very low (liquid Helium) temperatures. Initially a Boltzmann formalism is used to illustrate the effects of multiple sub-band occupancy. Structure is found in the electrical conductivity, thermal conductivity and thermopower when plotted as a function of chemical potential, due to the lateral quantisation of the electron states. These quantum size effects (QSE) are most pronounced in the thermopower, which is expected to show sign changes when the chemical potential sweeps through a sub-band minimum. A more sophisticated treatment based on Green's function methods reveals the importance of lifetime broadening in quasi-one-dimensional systems, which smears out the single-particle density of states and the QSE. The type of behaviour expected of realistic devices is explored, and it is shown that the thermopower offers the best chance of observing confinement effects. The formal theory may also be applied to the weak localisation corrections in multi-sub-band systems. An expression for the correction term is obtained which is valid for arbitrary channel width, and enables the crossover from a linear to logarithmic scaling in L. to be demonstrated. A transverse inelastic length is derived, and shown to be the length scale which controls the system dimensionality rather than Lφ. The implication for experiment in narrow channels is discussed. Weak localisation corrections are also calculated for the thermopower and the thermal conductivity. This corrects a result due to Ting et al (1982) that there are no weak localisation corrections to the thermopower in 2D. These results are shown to be a consequence of a rather general scaling theory of thermal transport which has wider implications, such as for the behaviour expected near a Metal-Insulator transition for example. Comparison with the single parameter scaling theory of the zero temperature conductance is made. Fluctuation effects for thermal transport in mesoscopic samples are also explored (both numerically and analytically), and the analogue of universal conductance fluctuations explicitly demonstrated.
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Schwiete, Georg. "Supermatrix models for disordered, chaotic and interacting electron systems". [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973471522.
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Merkt, Rainer. "Density of states and delocalization in low dimensional disordered electron systems". [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=960264817.
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Seiler, Christian [Verfasser] y F. [Akademischer Betreuer] Evers. "A functional renormalization group approach to interacting disordered electron systems / Christian Seiler ; Betreuer: F. Evers". Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/1124068643/34.
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Siegert, Christoph. "Disorder effects in two dimensional electron systems". Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612312.
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Slevin, Keith Martin. "Electrons in disorded one dimensional systems". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47666.
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Forestier, Guillaume. "Transport quantique dans les verres de spins". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY023/document.
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Les travaux expérimentaux présentés dans cette thèse associent deux pans de la physique de la matière condensée, avec d'un côté la physique des verres de spins et de l'autre la physique mésoscopique. Le verre de spins est un exemple emblématique de système désordonné et frustré, il se caractérise à basse température par un ordre magnétique non conventionnel, où le désordre magnétique apparaît gelé. De plus, celui-ci est considéré comme un système modèle pour étudier les verres en général et de ce fait, il a fait l'objet de nombreuses études expérimentales et théoriques. Après d'importants efforts de recherche, la description de l'état fondamental de ce système a abouti à deux approches très différentes. La première, donnée par la résolution non triviale du problème en champ moyen, met en avant un état fondamental composé d'une multitude d'états organisés et hiérarchisés. La deuxième approche, dite des "gouttelettes", se base quant à elle sur la dynamique hors équilibre d'un unique état. Cependant, en dépit de ces contributions, la compréhension de cette phase est loin d'être complète et la nature de l'état fondamental reste encore un débat ouvert. Dans un conducteur mésoscopique, le transport se fait de manière cohérente : les électrons gardent la mémoire de leur phase, ce qui permet d'observer des effets d'interférences électroniques. La motivation à la base de ce travail est d'utiliser ces effets d'interférences comme outil pour étudier le verre de spins. En effet, étant donné que les interférences électroniques dépendent intiment de la disposition du désordre statique du conducteur, le transport cohérent peut se révéler être une sonde microscopique très efficace pour étudier la configuration du désordre dans un conducteur. Bien que quelques expériences pionnières de transport cohérent existent dans des verres de spins, ce domaine de recherche n'a que très peu été exploré. Néanmoins, il a connu un récent renouveau grâce à des travaux théoriques qui montrent de quelle manière cette sonde est sensible au désordre magnétique gelé et comment elle peut fournir des informations sur la nature de l'état fondamental du verre de spins. Ainsi, ce travail de thèse expérimental présente l'implémentation de mesure de transport dans des verres de spins mésoscopiques. La première partie de l'étude est consacrée aux caractéristiques générales de transport classique et quantique de ces systèmes. Nous avons examiné les propriétés de la résistivité en fonction de la température et du champ magnétique et nous montrons que ces systèmes mésoscopiques possèdent bien des comportements attendus pour des verres de spins. Dans une deuxième partie, nous nous sommes intéressés au comportement de la magnétorésistance à bas. Nous avons mis en avant que celle-ci présente une forte hystérésis dont l'amplitude dépend fortement, de la température dans la phase vitreuse et de la vitesse de balayage du champ magnétique. Nous avons argumenté que ce comportement particulier traduit la mise hors équilibre du système et montrons comment la température et la vitesse de balayage du champ magnétique pilotent l'écart à l'équilibre. Dans cette partie, nous avons aussi examiné par des mesures de transport la relaxation du système vers l'équilibre, après l'avoir excité. Nous présentons également les propriétés de transport étonnantes que nous avons observées à bas champ, résultant de protocoles en températures et en champs magnétiques plus complexesThe experiments presented in this thesis associate two fields of condensed matter physic, on the one hand with the spin glass physic and the other hand with the mesoscopic physic. The spin glass state is one of the most emblematic of disordered and frustred system and at low temperature, it is caracterized by an unconventionel order where the magnetic disorder is quenched. Moroever, it is considered as a model system for glasses in general and thereby it has been extensively studied, both experimentally and theoreticlly. After extensive research efforts, the description of fundamental state of the system has lead towards two well different approaches. The first, given by the mean field solution, highlights a fundamental composed of mulitple states organised and hierarchical. The second, called droplet model is based on the off--equilibrium dynamic of a unique ground state. However, despite these contributions, the understanding ot this phase is far from being complete and the nature of the ground state still remains an open question. In a mesoscopic conductor, the transport of electron is coherent: electrons keep the memory of their phase, so that one can observe interference effects. The main motivation of this work is to use these interference effects in order to to probe the spin glass state. Indeed, as electronic interference depends of the position of the static disorder, coherent transport can be a useful tool to study the configuration of the microscopic disorder. Althought few coherent transport experiments exist to probe the spin glass, this field of research has very little explored. Nevertheless, this area has been a revival thanks to theoritical work, showing how coherent transport is sensitived to the quenched disorder and how it may provide informations of the nature of fundamental state of spin glass. So, this experimental work deals with the implementation of transport measurements in mesoscopic spin glasses. The first part of the study is focused on the general charateristics of classical and quatum transport of these system. We have examined the resistivity as a function of the temperature and magnetic field and we show that these mesoscopic systems have a spin glass-like behaviour. In a second part, we have focused on the low field magnetoresistivity. We show that it presents a strong hysteresis, whose the amplitude is strongly depends, both of the temperature in the glassy phase and sweeping rate of the magnetic field. We argue that this particular behaviour is related to the out off-equilibrium of the system and we show how the temperature and the sweeping rate control the deviation to the equilibrium. In this part, we also examine by transport measurements how the system relaxes towards the equilibrium just after its excitation. In addition, we present surprinsing transport propreties that we observed, resulting of experimental protocols more sophisticated in temperatures and magnetic fields
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Baenninger, Matthias. "Interaction effects and disorder in two-dimensional electron systems". Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/280142.
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This thesis reports an experimental study of transport on a mesoscopic lengthscale in the localised regime of two-dimensional electron systems (2DES) with varying disorder. Devices with dimensions of a few microns were fabricated from modulation doped GaAs/ AlGaAs heterostructures, where the strength of disorder was tuned by changing the width of the undoped spacer layer separating the 2DES from the charged dopants, which are the main source of disorder in these systems. The main motivation of the experiments was to study the interplay between electron-electron interactions and short-range disorder at low electron densities, while avoiding the impact of long-range charge inhomogeneities that are usually present in this regime. Indeed, several new observations have been achieved with this approach: Chapter 5 reports an universal behaviour of hopping magnetoresistance, with evidence of the average hopping distance being equal to the average electronelectron separation, and a quantisation of the hopping prefactor in units of the quantum of resistance h/e2. Chapter 6 discusses the temperature dependence of resistance. The main result is an apparent temperature driven metal-to-insulator transition with a crossover from activated transport at high temperatures to metallic transport at low temperatures. This observation persists to resistivities of several hundred times the quantum of resistance. In chapter 7 a new kind of resistance oscillations is reported, which appear as a function of electron density when a strong perpendicular magnetic field is applied. A strongly amplified pick-up of the Shubnikov-de Haas oscillation and a modification of t he quantum Hall effect are reported in chapter 8. Furthermore, a new technique for measuring the electron density in mesoscopic 2DES is presented in chapter 4.
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Winn, Martyn David. "Theoretical studies of the electronic properties of spatially disordered systems". Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279994.
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Pereira, Vítor Manuel. "Disorder and localization effects in correlated electronic systems". Tese, Porto : edição do autor, 2006. http://catalogo.up.pt/F?func=find-b&local_base=FCB01&find_code=SYS&request=000088367.
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Pereira, Vítor Manuel. "Disorder and localization effects in correlated electronic systems". Doctoral thesis, Porto : edição do autor, 2006. http://hdl.handle.net/10216/64278.
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Specht, Michael. "Etude expérimentale de systèmes désordonnés dans le régime de la localisation d'Anderson". Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10067.
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Ce travail est consacre a l'etude de la phase isolante de systemes desordonnes dans le regime de la localisation d'anderson. Les etats electroniques sont localises sur une echelle characteristique, la longueur de localisation, suite a des interferences destructives induites par le desordre. L'effet d'un champ magnetique sur la longueur de localisation a suscite plusieurs travaux theoriques recents. D'un cote la theorie de matrices aleatoires propose une dependance universelle de la longueur de localisation en fonction de la symmetrie du systeme. Un champ magnetique brise la symmetrie par rapport au renversement du sens du temps et peut induire un changement de la longueur de localisation quand un quantum de flux est mis a travers un site localise. D'un autre cote, la phase des fonctions d'onde lors d'un processus tunnel est sensible a un champ magnetique ce qui modifie l'element matriciel intersite. Pour etudier ces phenomenes nous nous sommes interesse dans un premier temps a la constante dielectrique. Cette quantite peut etre relie tres simplement a la longueur de localisation et represente donc une quantite tres importante si l'on s'interesse a la dependence de la longueur de localisation en fonction d'un champ magnetique applique. Par contre, a temperature finie un processus de relaxation de debye contribue a la constante dielectrique et doit etre separe dans une analyse des effets du champ. Nous presentons ici une etude assez complete de la constante dielectrique de systemes desordonnes yttrium-silicium en fonction d'un champ applique, de la temperature, de la frequence et de la longueur de localisation. Cette etude permet de bien separer l'effet du champ dans les differentes regimes et proche de la transition nous pouvons identifier un changement de la longueur de la localisation lorsqu'un quantum de flux est mise a travers un site localise. L'etude de la dependence en frequence montre que loin de la transition un modele de percolation permet de expliquer les lois d'echelle observe assez facilement. Proche de la transition, l'interaction coulombienne joue un role dominant a tres basse temperature et a l'aide d'un modele qui prend en compte un gap de coulomb dans la densite d'etat le comportement de la constante dielectrique est qualitativement bien decrit. Enfin nous avons etudie le magnetisme orbital dans les systemes yttrium-silicium tres proche de la transition. Nos resultats preliminaires suggerent que les effets sont induit par une brisure de la symmetrie par rapport au renversement du sens du temps, bien que une etude plus complete en fonction de la longueur de localisation est necessaire pour prouver l'origine orbital du signal observe.
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Ruess, Frank Joachim Physics Faculty of Science UNSW. "Atomically controlled device fabrication using STM". Awarded by:University of New South Wales. Physics, 2006. http://handle.unsw.edu.au/1959.4/24855.
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We present the development of a novel, UHV-compatible device fabrication strategy for the realisation of nano- and atomic-scale devices in silicon by harnessing the atomic-resolution capability of a scanning tunnelling microscope (STM). We develop etched registration markers in the silicon substrate in combination with a custom-designed STM/ molecular beam epitaxy system (MBE) to solve one of the key problems in STM device fabrication ??? connecting devices, fabricated in UHV, to the outside world. Using hydrogen-based STM lithography in combination with phosphine, as a dopant source, and silicon MBE, we then go on to fabricate several planar Si:P devices on one chip, including control devices that demonstrate the efficiency of each stage of the fabrication process. We demonstrate that we can perform four terminal magnetoconductance measurements at cryogenic temperatures after ex-situ alignment of metal contacts to the buried device. Using this process, we demonstrate the lateral confinement of P dopants in a delta-doped plane to a line of width 90nm; and observe the cross-over from 2D to 1D magnetotransport. These measurements enable us to extract the wire width which is in excellent agreement with STM images of the patterned wire. We then create STM-patterned Si:P wires with widths from 90nm to 8nm that show ohmic conduction and low resistivities of 1 to 20 micro Ohm-cm respectively ??? some of the highest conductivity wires reported in silicon. We study the dominant scattering mechanisms in the wires and find that temperature-dependent magnetoconductance can be described by a combination of both 1D weak localisation and 1D electron-electron interaction theories with a potential crossover to strong localisation at lower temperatures. We present results from STM-patterned tunnel junctions with gap sizes of 50nm and 17nm exhibiting clean, non-linear characteristics. We also present preliminary conductance results from a 70nm long and 90nm wide dot between source-drain leads which show evidence of Coulomb blockade behaviour. The thesis demonstrates the viability of using STM lithography to make devices in silicon down to atomic-scale dimensions. In particular, we show the enormous potential of this technology to directly correlate images of the doped regions with ex-situ electrical device characteristics.
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Kneten, Kristin Renae. "Effects of redox system structure on electron transfer kinetics at ordered graphite and disordered carbon electrodes /". The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487848078450307.
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Yildiz, Abdulkadir. "A new technique to calculate the electronic structure of disordered and quasicrystal systems in two-dimensions". Thesis, University of Leicester, 1995. http://hdl.handle.net/2381/35837.
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The purpose of this work is to investigate the electronic structure of two-dimensional structurally disordered solids and quasicrystals by means of the Beeby and Hayes method which is based on multiple scattering theory. Using this method, the formal expressions for a two-dimensional system, such as the dynamical matrix and the spectral density, are determined in terms of a self-consistent function. The expressions are then applied to two-dimensional models to evaluate the densities of electronic states. Two principal issues are investigated in the calculations of the density of states. One is to illustrate the convergence of the method through the results of calculations. The other issue is to observe the variation of densities of electronic states with- respect to varying the disorder in the structure. For the first case, different sizes of the dynamical matrix, which correspond to the atomic structure of the system, are solved, and for each matrix the density of states is calculated. It is found that the densities of states for a disordered system do not change after the matrix size (NxN) exceeds 101x101. In the second case, some particular models are chosen, such as 3-fold, 4-fold, 5-fold and 6-fold coordinated sites, and the densities of states are calculated for each model. It is shown that the densities of states vary significantly with increasing disorder in the structure. The electronic structure of a two-dimensional quasicrystal, i.e. a Penrose lattice, has also been investigated in the tight binding limit using this approach. We have in particular studied the vertex model of the lattice and calculated the density of electronic states and integrated density of electronic states. The method used is effectively for an infinite structure and produces no distortions from edge effects or periodic continuation. The vertex model, which is based on fat and thin rhombi, has three nearest interatomic distances, the short diagonal of a thin rhombus, the edge of a rhombus, and the short diagonal of a fat rhombus. We have found the effect of interactions involving these various distances in the DOS. For example, there exists a very high central peak at zero energy if only the shortest is taken, the peak disappears if the first and second shortest distances are taken, and when all three distances are included there are no gaps and no central peak. The density of electronic states is asymmetric in all three cases.
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Shrestha, Kiran (Engineer). "Electrical Conduction Mechanisms in the Disordered Material System P-type Hydrogenated Amorphous Silicon". Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc700106/.
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The electrical and optical properties of boron doped hydrogenated amorphous silicon thin films (a-Si) were investigated to determine the effect of boron and hydrogen incorporation on carrier transport. The a-Si thin films were grown by plasma enhanced chemical vapor deposition (PECVD) at various boron concentrations, hydrogen dilutions, and at differing growth temperatures. The temperature dependent conductivity generally follows the hopping conduction model. Above a critical temperature, the dominant conduction mechanism is Mott variable range hopping conductivity (M-VRH), where p = ¼, and the carrier hopping depends on energy. However, at lower temperatures, the coulomb interaction between charge carriers becomes important and Efros-Shklosvkii variable hopping (ES-VRH) conduction, where p=1/2, must be included to describe the total conductivity. To correlate changes in electrical conductivity to changes in the local crystalline order, the transverse optical (TO) and transverse acoustic (TA) modes of the Raman spectra were studied to relate changes in short- and mid-range order to the effects of growth temperature, boron, and hydrogen incorporation. With an increase of hydrogen and/or growth temperature, both short and mid-range order improve, whereas the addition of boron results in the degradation of short range order. It is seen that there is a direct correlation between the electrical conductivity and changes in the short and mid-range order resulting from the passivation of defects by hydrogen and the creation of trap states by boron. This work was done under the ARO grant W911NF-10-1-0410, William W. Clark Program Manager. The samples were provided by L-3 Communications.
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Zeng, Li. "Disordered electronic and magnetic systems - transition metal (Mn) and rare earth (Gd) doped amorphous group IV semiconductors (C, Si, Ge)". Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3284117.
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Thesis (Ph. D.)--University of California, San Diego, 2007.Title from first page of PDF file (viewed January 9, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 123-132).
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Rowlands, Derwyn Andrew. "The Korringa-Kohn-Rostoker nonlocal coherent-potential approximation : a new method for calculating the electronic structure of disordered metallic systems". Thesis, University of Warwick, 2004. http://wrap.warwick.ac.uk/59515/.
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The limitations of the current 'first-principles' effective medium approach to calculating the electronic structure of disordered systems are described. These limitations can be addressed by a cluster theory, and only very recently the first satisfactory cluster theory, the nonlocal coherent potential approximation, has been developed within a tight-binding framework. However an approach based on KKR multiple scattering is needed in order to treat the problem from first principles for ab-initio calculations. In this thesis, these ideas are reformulated in terms of multiple scattering theory and the Korringa-Kohn-Rostoker non-local coherent potential approximation (KKR-NLCPA) is introduced for describing the electronic structure of disordered systems. The KKR-NLCPA systematically provides a hierarchy of improvements upon the widely used local mean-field KKR-CPA approach and includes nonlocal correlations in the disorder configurations by means of a self-consistently embedded cluster. The KKR-NLCPA method satisfies all of the requirements for a successful cluster generalisation of the KKR-CPA; it determines a site-to-site translationally-invariant effective medium, it is herglotz analytic, becomes exact in the limit of large cluster sizes, reduces to the KKR-CPA for a single-site cluster, is straightforward to implement numerically, and enables the effects of short-range order upon the electronic structure to be investigated. In particular, it is suitable for combination with electronic density functional theory to give an ab-initio description of disordered systems. Future applications to charge correlation and lattice displacement effects in alloys and spin fluctuations in magnets amongst others are very promising. The method is illustrated by application to a simple one-dimensional model.
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Selm, Leo Joseph. "A family systems approach to treatment of addictive disorders confluence of two existing constructs /". View full text, 2002.
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Song, Yi. "AC conductivity and dielectric constant of systems near the percolation threshold /". The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu148726754698361.
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Römer, Rudolf A. "From localization to delocalization in disordered systems numerical studies of the influence of disorder and many-body interactions on the electronic transport properties of solids = Von Lokalisierung zu Delokalisierung in ungeordneten Systemen : numerische Untersuchungen zum Einfluß von Unordnung und Wechselwirkung auf die elektronischen Transporteigenschaften von Festkörpern /". [S.l. : s.n.], 2000. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9494962.
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Chemnitz, Techn. Univ., Habil.-Schr., 1999.Teilw. u.d.T.: From localization to delocalization: numerical studies of transport in disordered systems. Parallelt.: Von Lokalisierung zu Delokalisierung in ungeordneten Systemen.
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Dyck, Richard Henry. "Cytochrome oxidase histopathology in the central nervous system of developing rats displaying methylmercury-induced movement and postural disorders". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/27873.
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Sprague-Dawley rats were administered daily, subcutaneous injections of methylmercuric chloride at a dose of 5 mg/Hg/kg beginning on postnatal day 5. By their fourth postnatal week, animals exhibited a constellation of neurological signs of motor impairment which resembled the cerebral palsy syndrome of humans perinatally exposed to methylmercury. Routine histological examination of the brain revealed no gross differences between methylmercury-treated (MeHg), normal control (NC) or weight-matched littermates.
The histochemical localization of the mitochondrial enzyme cytochrome oxidase (CO) was utilized in Experiment I to examine possible alterations in the metabolic activity of motor nuclei which might contribute to the observed movement and postural disorders. A population of intensely-staining cytochrome oxidase neurons (ICONs) in the magnocellular portion of the red nucleus (RMC) and interrubral mesencephalon (IRM) were conspicuously present in all MeHg animals at the onset of motor impairment. These morphologically, histochemically, and anatomically distinct neurons did not exhibit intense CO staining in control animals. Conversely, a significant decrease was demonstrated in the oxidative metabolic activity of many neurons in the substantia nigra, zona reticulata of MeHg animals.
In Experiment II, the postnatal appearance of ICONs was morphometrically quantified in MeHg animals sacrificed at PND 14, 16, 18, 20, 22, or 25. The histochemically-defined onset of increased metabolic activity in ICONs was first observed on PND 16, at least one week before the onset of clinical signs of neurological impairment. This was the earliest manifestation of methylmercury neurotoxicity yet described in this animal model. A subsequent four-fold increase in the total number of ICONs at PND 18 was followed by a gradual decrease in number to PND 25. Significantly more of the ICONs were found in the IRM than in the RMC at PND 18 & 20.
The possibility that the increased activity of ICONs may result from disinhibition of specific afferents to the red nucleus was addressed by introducing either hemidecortication or hemicerebellectomy on PND 10 and then morphometrically determining the deviation from symmetry in the bilateral distribution of the total number of ICONs in the RMC and IRM at PND 22. The distribution of ICONs was symmetrical and not different in either hemidecorticate or unoperated controls. A significant (36%) decrease in the total number of ICONs was observed in both the RMC and IRM contralateral to hemicerebellectomy. The identical ipsilateral regions did not differ from control or hemidecorticate MeHg animals.
In Experiment III, the anatomical distribution of major histocompatability complex antigens (MHC) in the brain of MeHg animals was examined using immunohistochemical methods. MHC immunoreactivity was widely distributed throughout the brain of MeHg animals. Areas with low immunoreactivity, or lack of it, stand out and include all of the hippocampus, thalamus, pyriform and entorhinal cortex, and lateral cerebellar hemispheres. Moderate staining intensity was observed in neocortical areas, basal forebrain, caudate-putamen and cerebellar vermis. Strong immunoreactivity was found in red nucleus, substantia nigra, cingulate cortex, retrosplenial cortex, presubiculum, parasubiculum and vestibular nuclei.
It was suggested that the increased activity of ICONs likely contributes to the movement and postural disorders resulting from methylmercury intoxication. The increased activity in ICONs was determined to be, at least partially, dependent upon cerebellar input. The results are discussed with reference to the toxic effects of methylmercury and specifically to the susceptibility of GABAergic interneurons in perinatal trauma. Possible analogies are drawn between the mechanisms of methylmercury-induced cerebral palsy syndrome and those of other developmental movement and postural disorders.Medicine, Faculty of
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Langenfeld, Annette. "Etude de corrélations électroniques dans des systèmes désordonnés". Grenoble 1, 1993. http://www.theses.fr/1993GRE10081.
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Cette these est faite de deux parties independantes. La premiere partie traite les corrections quantiques a l'effet hall anormal. On peut montrer que les termes de l'anomalie coulombienne se compensent mutuellement en considerant la diffusion asymetrique des electrons de conduction par les moments magnetiques d'une couche metallique desordonnee. La contribution venant de la localisation faible est coupee par la diffusion asymetrique qui brise la coherence de phase. Les resultats sont en bon accord avec une experience recente sur des couches minces de fer desordonnees et ferromagnetiques. Dans la seconde partie, on etudie la formation de moments magnetiques localises dans des systemes comme des semiconducteurs dopes en phase metallique. Le calcul est base sur le modele de hubbard avec desordre hors-diagonal. En examinant le modele a une seule impurete faiblement rattachee au reseau, on trouve un moment magnetique localise, et cela meme dans l'approximation de hartree-fock pour la repulsion locale u. On associe a ce moment magnetique un effet kondo dont la nature et la dependance par rapport au desordre sont discutees. Les resultats sont compares a une experience recente mesurant le pouvoir thermoelectrique du si:p. La correspondance est satisfaisante
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Silva, James Clauton da [UNESP]. "Diagnóstico de distúrbios de tensão em sistemas de distribuição de energia elétrica usando um algoritmo imuno-neural". Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/115849.
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000808453.pdf: 1098297 bytes, checksum: 99a8ff6015e19ecb65fcf8b48a61bf82 (MD5)Nesta pesquisa, apresenta-se uma nova abordagem para o diagnóstico de distúrbios de tensão em sistemas de distribuição de energia elétrica, usando como ferramenta um algoritmo Imuno-Neural. Trata-se, basicamente, de realizar a junção de um algoritmo imunológico de seleção negativa com uma rede neural artificial ARTMAP-Fuzzy. Partindo-se das medições realizadas em uma subestação de distribuição por um sistema de aquisição de dados SCADA, um módulo imunológico é empregado para realizar a detecção, identificando anormalidades por meio de um janelamento das curvas oscilográficas, separando, desta forma, o sinal em parcelas menores para a análise. Assim, no módulo neural, a classificação das anormalidades é realizada. A principal aplicação desta nova ferramenta é auxiliar na tomada de decisões e facilitar a operação do sistema durante a ocorrência de perturbações de tensão. Visando ilustrar a eficiência do método proposto, foram realizadas simulações de sistemas de distribuição de energia elétrica contendo 33, 84 e 134 barras, respectivamente, usando-se o aplicativo EMTP. Os resultados obtidos com esta nova abordagem evidenciam uma melhoria em termos de eficiência e de precisão, quando comparados à literatura
In this research we present a new approach to the diagnosis of voltage disturbances in power distribution systems, using as one tool Immune Neural algorithm. This proposal is basically to hold the junction of an immune negative selection algorithm with an artificial neural network ARTMAP-Fuzzy. Thus, starting from measurements made in a distribution substation for SCADA system for acquiring data, an immunological module performs the detection process, identifying abnormalities through a windowing performed by the oscillographic curves, thereby separating the signal into smaller portions for analysis module and so on neural classification of abnormality is performed. The main application of this new tool is to assist in decision making and facilitate the operation of the system for failures. To evaluate the efficiency of the proposed method simulations of electric power distribution systems were performed in three systems EMTP software distribution containing 33, 84 and 134 bar, respectively. The results obtained with this new approach demonstrate accuracy and efficiency when compared to literature
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Silva, James Clauton da. "Diagnóstico de distúrbios de tensão em sistemas de distribuição de energia elétrica usando um algoritmo imuno-neural /". Ilha Solteira, 2014. http://hdl.handle.net/11449/115849.
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Orientador: Carlos Roberto MinussiBanca: Francisco Villarreal Alvarado
Banca: Fernando Cezar Vieira Malange
Resumo: Nesta pesquisa, apresenta-se uma nova abordagem para o diagnóstico de distúrbios de tensão em sistemas de distribuição de energia elétrica, usando como ferramenta um algoritmo Imuno-Neural. Trata-se, basicamente, de realizar a junção de um algoritmo imunológico de seleção negativa com uma rede neural artificial ARTMAP-Fuzzy. Partindo-se das medições realizadas em uma subestação de distribuição por um sistema de aquisição de dados SCADA, um módulo imunológico é empregado para realizar a detecção, identificando anormalidades por meio de um janelamento das curvas oscilográficas, separando, desta forma, o sinal em parcelas menores para a análise. Assim, no módulo neural, a classificação das anormalidades é realizada. A principal aplicação desta nova ferramenta é auxiliar na tomada de decisões e facilitar a operação do sistema durante a ocorrência de perturbações de tensão. Visando ilustrar a eficiência do método proposto, foram realizadas simulações de sistemas de distribuição de energia elétrica contendo 33, 84 e 134 barras, respectivamente, usando-se o aplicativo EMTP. Os resultados obtidos com esta nova abordagem evidenciam uma melhoria em termos de eficiência e de precisão, quando comparados à literatura
Abstract: In this research we present a new approach to the diagnosis of voltage disturbances in power distribution systems, using as one tool Immune Neural algorithm. This proposal is basically to hold the junction of an immune negative selection algorithm with an artificial neural network ARTMAP-Fuzzy. Thus, starting from measurements made in a distribution substation for SCADA system for acquiring data, an immunological module performs the detection process, identifying abnormalities through a windowing performed by the oscillographic curves, thereby separating the signal into smaller portions for analysis module and so on neural classification of abnormality is performed. The main application of this new tool is to assist in decision making and facilitate the operation of the system for failures. To evaluate the efficiency of the proposed method simulations of electric power distribution systems were performed in three systems EMTP software distribution containing 33, 84 and 134 bar, respectively. The results obtained with this new approach demonstrate accuracy and efficiency when compared to literature
Mestre
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Andrade, Eric de Castro e. "Cálculos numéricos de sistemas eletrônicos desordenados correlacionados". [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277676.
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Orientador: Eduardo MirandaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Sistemas eletrônicos fortemente correlacionados desordenados possuem dois mecanismos básicos para a localização eletrônica e a subsequente destruição do estado metálico: o de Mott (causado pela interação elétron-elétron) e o de Anderson (causado pela desordem). Nesta tese, estudamos como estes mecanismos competem dentro da fase metálica e também como afetam o comportamento crítico do sistema, empregando uma generalização para o caso desordenado do cenário de Brinkman-Rice para a transição de Mott. Investigamos os efeitos de desordem fraca e moderada sobre a transição metal-isolante de Mott a T = 0 em duas dimensões. Para desordem sucientemente baixa, a transição mantém sua característica do tipo Mott, na qual temos os pesos de quasipartícula Zi indo a zero na transição e uma forte blindagem da desordem na região crítica. Em contraste com o comportamento encontrado para d = 8 , no nosso caso as flutuações espaciais dos pesos de quasipartícula são fortemente amplificadas próximo à transição de Mott de tal forma que eles adquirem uma distribuição do tipo lei de potência P (Z) ~ Z a-1 ,com a --> 0 na transição. Tal comportamento altera completamente as características desta transição com relação ao caso limpo, e é um indício robusto da emergência de uma fase de Griffiths eletrônica precedendo a transição metal-isolante de Mott, com uma fenomenologia surpreendentemente similar àquela do "ponto fixo de desordem infinita" encontrada em magnetos quânticos. Uma consequência imediata dessas novas características introduzidas pela desordem é que estados eletrônicos próximos à superfície de Fermi tornam-se mais homogêneos na região crítica, ao passo que estados com maiores energias têm o comportamento oposto: eles apresentam uma grande inomogeneidade precisamente nas vizinhanças da transição de Mott. Sugerimos que uma desordem efetiva dependente da interação é uma característica comum a todos os sistemas de Mott desordenados. Estudamos também como os efeitos bem conhecidos das oscilações de longo alcance de Friedel são afetados por fortes correlações eletrônicas. Primeiramente, mostramos que sua amplitude e alcance são consideravelmente suprimidos em líquidos de Fermi fortemente renormalizados. Posteriormente, investigamos o papel dos espalhamentos elásticos e inelásticos na presença dessas oscilações. Em geral, nossos resultados analíticos mostram que um papel proeminente das oscilações de Friedel é relegado a sistemas fracamente interagentes. Abordamos, por m, os efeitos das interações sobre o isolante de Anderson em uma dimensão. Construímos a função de escala ß (g) e mostramos que a escala de "crossover" g *, que marca a transição entre o regime ôhmico e o localizado da condutância, é renormalizada pelas interações. Como consequência, embora não haja a emergência de estados verdadeiramente estendidos, o regime ôhmico de g estende-se agora por uma região consideravelmente maior do espaço de parâmetros.
Abstract: Disordered strongly correlated electronic systems have two basic routes towards localization underlying the destruction of the metallic state: the Mott route (driven by electron-electron interaction) and the Anderson route (driven by disorder). In this thesis, we study how these two mechanisms compete in the metallic phase, and also how they change the critical behavior of the system, within a generalization to the disordered case of the Brinkman-Rice scenario for the Mott transition. We investigate the effects of weak to moderate disorder on the Mott metal-insulator transition at T = 0 in two dimensions. For sufficiently weak disorder, the transition retains the Mott character, as signaled by the vanishing of the local quasiparticle weights Zi and strong disorder screening at criticality. In contrast to the behavior in d = 8, here the local spatial fluctuations of quasiparticle parameters are strongly enhanced in the critical regime, with a distribution function P(Z) ~ Z a-1 and a --> 0 at the transition. This behavior indicates the robust emergence of an electronic Griffiths phase preceding the MIT, in a fashion surprisingly reminiscent of the " Infinite Randomness Fixed Point" scenario for disordered quantum magnets. As an immediate consequence of these new features introduced by disorder, we have that the electronic states close to the Fermi energy become more spatially homogeneous in the critical region, whereas the higher energy states show the opposite behavior: they display enhanced spatial inhomogeneity precisely in the close vicinity to the Mott transition. We suggest that such energy-resolved disorder screening is a generic property of disordered Mott systems. We also study how well-known effects of the long-ranged Friedel oscillations are affected by strong electronic correlations. We first show that their range and amplitude are signifficantly suppressed in strongly renormalized Fermi liquids. We then investigate the interplay of elastic and inelastic scattering in the presence of these oscillations. In the singular case of two-dimensional systems, we show how the anomalous ballistic scattering rate is conned to a very restricted temperature range even for moderate correlations. In general, our analytical results indicate that a prominent role of Friedel oscillations is relegated to weakly interacting systems. Finally, we discuss the effects of correlations on the Anderson insulator in one dimension. We construct the scaling function ß(g) and we show that the crossover scaling g*, which marks the transition between the ohmic and the localized regimes of the conductance, is renormalized by the interactions. As a consequence, we show that, although truly extend states do not emerge, the ohmic regime covers now a considerably larger region in the parameter space.
Doutorado
Física da Matéria Condensada
Doutor em Ciências
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Zschornak, Matthias [Verfasser], Dirk C. [Akademischer Betreuer] Meyer, Dirk C. [Gutachter] Meyer y Sibylle [Gutachter] Gemming. "Defect-induced local electronic structure modifications within the system SrO - SrTiO3 - TiO2 : symmetry and disorder / Matthias Zschornak ; Gutachter: Dirk C. Meyer, Sibylle Gemming ; Betreuer: Dirk C. Meyer". Freiberg : Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2015. http://d-nb.info/1220912123/34.
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Akkermans, Éric. "Propagation d'ondes dans les milieux désordonnés". Grenoble 1, 1986. http://www.theses.fr/1986GRE10050.
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Les phenomenes etudies font intervenir la phase de l'onde et la dimensionalite de l'espace de propagation. Dans le cas des systemes uni et bidimensionnels, les ondes subissant des collisions multiples elastiques interferent fortement et conduisent a des modes propres exponentiellement localises. Leur structure est etudiee sur la base d'un modele particulier de potentiel incommensurable. Le transport des phonons et des electrons dans les systemes unidimensionnels desordonnes a ete plus generalement caracterise
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Burdin, Sébastien. "Théories de champ moyen pour les systèmes d'électrons à fortes corrélations". Habilitation à diriger des recherches, Université Sciences et Technologies - Bordeaux I, 2012. http://tel.archives-ouvertes.fr/tel-00711167.
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Ce mémoire d'habilitation à diriger les recherches présente des théories de champ moyen que j'ai appliquées à l'étude de systèmes d'électrons à fortes corrélations. Il s'appuie sur des travaux que j'ai effectués, pour certains dans la continuité de ma thèse, pour d'autres dans des directions nouvelles. L'une des problématiques centrales est celle des transitions de phases quantiques, et les systèmes considérés ont le point commun de décrire des impuretés quantiques, réelles ou artificielles. Les différentes méthodes de champ moyen utilisées sont présentées par des exemples dans le cadre de problèmes physiques particuliers. Après un premier chapitre introductif fortement focalisé sur l'exemple des composés d'électrons f, ce mémoire est structuré en trois chapitres principaux connectés respectivement aux trois thématiques suivantes : les composés Kondo, les liquides de spin, et les systèmes désordonnés.
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Pereira, Ana Luiza Cardoso 1976. "Destino dos estados estendidos e origem dos estados localizados no regime Hall quântico". [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277032.
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Orientadores: Peter A. B. Schulz, John T. ChalkerTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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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
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Paulin, Guillaume. "Transport électronique et Verres de Spins". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2010. http://tel.archives-ouvertes.fr/tel-00556836.
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The results reported in this thesis contribute to the understanding of disordered systems, to mesoscopic physics on the one hand, and to the physics of spin glasses on the other hand. The first part of this thesis studies numerically coherent electronic transport in a non magnetic metal accurately doped with frozen magnetic impurities (a low temperature spin glass). Thanks to a recursive code that calculates the two terminal conductance of the system, we study in detail the metallic regime of conduction (large conductance) as well as the insulating regime (small conductance). In both regimes, we highlight a universal behavior of the system. Moreover, a study of correlations between the conductance of different spin configurations of impurities allows us to link these correlations with correlations between spin configurations. This study opens the route for the first experimental determination of the overlap via transport measurements. A second part of this thesis deals with the study of the mean field Sherrington-Kirkpatrick model, which describes the low temperature phase of an Ising spin glass. We are interested here in the generalization of this model to quantum spins (i.e including the possibility to flip by quantum tunneling) of this classical model that was well studied during the past thirty years. We deduce analytically motion equations at the semi-classical level, for which the influence of quantum tunneling is weak, and we compare them with the classical case. We finally solve numerically these equations using a pseudo-spectral method.
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Adroguer, Pierre. "Propriétés de transport électronique des isolants topologiques". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2013. http://tel.archives-ouvertes.fr/tel-00832048.
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Les travaux présentés dans cette thèse ont pour objectif d'apporter à la physique mésoscopique un éclairage concernant la compréhension des propriétés de transport électroniques d'une classe de matériaux récemment découverts : les isolants topologiques.La première partie de ce manuscrit est une introduction aux isolants topologiques, mettant en partie l'accent sur leurs spécificités par rapport aux isolants "triviaux" : des états de bords hélicaux (dans le cas de l'effet Hall quantique de spin en 2 dimensions) ou de surface relativistes (pour les isolants topologiques tridimensionnels) robustes vis-à-vis du désordre.La deuxième partie propose une sonde de l'hélicité des états de bords de l'effet Hall quantique de spin en étudiant les propriétés remarquables de l'injection de paires de Cooper dans cette phase topologique.La troisième partie étudie la diffusion des états de surface des isolants topologiques tridimensionnels dans le régime cohérent de phase. L'étude de la diffusion, de la correction quantique à la conductance (antilocalisation faible) et de l'amplitude des fluctuations universelles de conductance de fermions de Dirac sans masse est présentée. Cette étude est aussi menée dans la cas d'états de surface dont la surface de Fermi présente la déformation hexagonale observée expérimentalement.
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Lepage, Hadrien. "Modélisation de solides à nanocristaux de silicium". Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00753248.
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Les propriétés physico-chimiques d'un nanocristal semi-conducteur sphérique, intermédiaires entre la molécule et le solide, dépendent de sa taille. Empilés ou dispersés, ces nanocristaux sont les briques architecturales de nouveaux matériaux fonctionnels aux propriétés ajustables, en particulier pour l'optoélectronique. Cette thèse s'inscrit dans le développement de ces nouveaux matériaux et présente avant tout une méthodologie pour la simulation du transport électronique dans un solide à nanocristaux en régime de faible couplage électronique appliquée à des nanocristaux de silicium dans une matrice de SiO2 pour les applications photovoltaïques. La cinétique du déplacement des porteurs est liée au taux de transfert tunnel (hopping) entre nanocristaux. Ces taux sont calculés dans le cadre de la théorie de Marcus et prennent en compte l'interaction électron-phonon dont l'effet du champ de polarisation dans la matrice ainsi que les interactions électrostatiques à courte et longue portée. Le calcul des états électroniques (électrons et trous) en théorie k.p associé à l'utilisation de la formule de Bardeen donne au code la capacité, par rapport à la littérature, de fournir des résultats (mobilité ou courant) en valeur absolue. Les résultats de mobilité ainsi obtenus pour des empilements cubiques idéaux viennent contredire les résultats de la littérature et incitent à considérer d'autres matériaux notamment en ce qui concerne la matrice pour obtenir de meilleurs performances. En outre, les résultats de simulation de dispositifs montrent l'impact considérable des électrodes sur les caractéristiques courant-tension. Aussi, un nouvel algorithme Monte-Carlo Cinétique accéléré a été adapté afin de pouvoir reproduire le désordre inhérent à la méthode de fabrication tout en maintenant un temps de simulation raisonnable. Ainsi l'impact du désordre en taille se révèle faible à température ambiante tandis que les chemins de percolation occultent la contribution des autres chemins de conduction. Des résultats de caractérisation comparés aux simulations tendent par ailleurs à indiquer que ces chemins peuvent concentrer les porteurs et exhiber un phénomène de blocage de coulomb. Enfin, la section efficace d'absorption est calculée théoriquement et permet d'obtenir le taux de génération sous illumination qui se révèle proche du silicium massif. Et une méthode en microscopie à sonde de Kelvin est décrite pour caractériser la durée de vie des porteurs c'est-à-dire le taux de recombinaison, les résultats ainsi obtenus étant cohérents avec d'autres techniques expérimentales.
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Schwiete, Georg [Verfasser]. "Supermatrix models for disordered, chaotic and interacting electron systems / von Georg Schwiete". 2004. http://d-nb.info/973471522/34.
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Merkt, Rainer [Verfasser]. "Density of states and delocalization in low dimensional disordered electron systems / vorgelegt von Rainer Merkt". 2000. http://d-nb.info/960264817/34.
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Zou, Yue. "Quantum Phases and Phase Transitions in Disordered Low-Dimensional Systems: Thin Film Superconductors, Bilayer Two-Dimensional Electron Systems, and One-Dimensional Optical Lattices". Thesis, 2011. https://thesis.library.caltech.edu/6024/2/thesis_v5.pdf.
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The study of various quantum phases and the phase transitions between them in low-dimensional disordered systems has been a central theme of recent developments of condensed matter physics. Examples include disordered thin film superconductors, whose critical temperature and density of states can be affected by a normal metallic layer deposited on top of them; amorphous thin films exhibiting superconductor-insulator transitions (SIT) tuned by disorder or magnetic field; and bilayer two-dimensional electron systems at total filling factor ν=1, which exhibit interlayer coherent quantum Hall state at small layer separation and have a phase transition tuned by layer separation, parallel magnetic field, density imbalance, or temperature. Although a lot of theoretical and experimental investigations have been done, many properties of these phases and natures of the phase transitions in these systems are still being debated. Here in this thesis, we report our progress towards a better understanding of these systems. For disordered thin film superconductors, we first propose that the experimentally observed lower-than-theory gap-Tc ratio in bilayer superconducting-normal-metal films is due to inhomogeneous couplings. Next, for films demonstrating superconductor-insulator transitions, we propose a new type of experiment, namely the drag resistance measurement, as a method capable of pointing to the correct theory among major candidates such as the quantum vortex picture and the percolation picture. For bilayer two-dimensional electron systems, we propose that a first-order phase transition scenario and the resulting Clausius-Clapeyron equations can describe various transitions observed in experiments quite well. Finally, in one-dimensional optical lattices, we show that one can engineer the long-sought-after random hopping model with only off-diagonal disorder by fast-modulating an Anderson insulator.
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Khan, Niaz Ali. "Correlated Disorder in One-dimensional Electronic Systems". Tese, 2019. https://hdl.handle.net/10216/122099.
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Khan, Niaz Ali. "Correlated Disorder in One-dimensional Electronic Systems". Doctoral thesis, 2019. https://hdl.handle.net/10216/122099.
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Tanasković, Darko Dobrosavljevic Vladimir. "Anomalous metallic behavior in strongly correlated electron systems with disorder". Diss., 2005. http://etd.lib.fsu.edu/theses/available/etd-07082005-202115.
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Thesis (Ph. D.)--Florida State University, 2005.Advisor: Dr. Vladimir Dobrosavljevic, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Sept. 20, 2005). Document formatted into pages; contains ix, 126 pages. Includes bibliographical references.
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Hsu, Hsiu-Chuan y 許琇娟. "Effects of Disorder on Spin Hall Conductivityin Two Dimensional Electron Systems". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/23440691702132772959.
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碩士國立臺灣大學
物理研究所
96
The novel phenomenon of intrinsic spin Hall e ect (ISHE) is that a dissipationless transverse spin-polarized current being induced only by applying an external electric field in a spin-orbit coupling material. It is unlike the extrinsic SHE, which arises from being scattered by the spin-orbit coupling impurities. However, the interplay between disorder and ISHE is still unclear. To understand whether the presence of disorder reduces or has no effect on the intrinsic value is important in predicting experimental detections. On the other hand, since the lateral movement of electrons in spin Hall effect can be recognized as the orbital motion, ISHE always accompanies the orbital angular momentum (OAM) Hall effect. The OAM Hall conductivity is the same in magnitude, but opposite in sign with the spin Hall conductivity (SHC) in the Rashba model. The suppression of SHC in the disordered Rashba model has already been studied by several authors, but the disorder effect on the OAM Hall e ect has not yet been known. In this thesis, the effects of short-ranged and spin-independent disorder on spin Hall conductivity in the Rashba, Dresselhaus and wurtzite model and on OAM Hall conductivity in the Rashba model and the Dresselhaus model have been studied in the linear response regime. Two methods were employed, the vertex correction within the ladder approximation and by the momentum relaxation time approximation. The effective conserved spin current gives the insights into the spin torque contribution to the ISHC. We found that by momentum relaxation time approximation, the spin torque contribution was one order smaller than the conventional contribution in the disordered system. Moreover, the SHC calculated from the effective conserved spin Hall current changed sign from the intrinsic system to the disordered system, while the SHC calculated from the conventional spin Hall current did not change sign. Results from the two methods imply that the spin torque contribution to the SHC may be from the electrons in the Fermi sea, unlike the conventional contribution to the SHC, which was from the electrons at the Fermi level. The results of the vertex correction of OAM Hall conductivity had a divergent term in the d.c. limit. The divergent term was due to the gauge dependent property of the ill-defined position operator in momentum space. Nonetheless, the OAM Hall conductivities recovered e/8pi in the ballistic limit and vanished in the diordered limit when only the interband contribution was taken into account. How to solve this ambiguity is still under study.
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Hsu, Hsiu-Chuan. "Effects of Disorder on Spin Hall Conductivity in Two Dimensional Electron Systems". 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2107200815240000.
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Aamir, Mohammed Ali. "Impact of Disorder and Topology in Two Dimensional Systems at Low Carrier Densities". Thesis, 2016. http://hdl.handle.net/2005/3118.
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Two dimensional (2D) systems with low carrier density is an outstanding platform for studying a wide spectrum of physics. These include both classical and quantum effects, arising from disorder, Coulomb interactions and even non-trivial topological properties of band-structure. In this thesis, we have explored the physics at low carrier number density in GaAs/AlGaAs heterostructure and bilayer graphene, by investigating in a larger phase space using a variety of electrical measurement tools.
A two-dimensional electron system (2DES) formed in a GaAs/AlGaAs heterostructure offers an avenue to build a variety of mesoscopic devices, primarily because its surface gates can very effectively control its carrier density profile. In the first half of the thesis, we study the relevance of disorder in two kinds of devices made in a 2DES. A very strong negative gate voltage not only reduces the carrier density of the 2DES, but also drives it to a disordered state. In this state, we explore a new direction in parameter space by increasing in-plane electric field and investigating its magneto-resistance (MR). At sufficiently strong gate voltage and source-drain bias, we discover a remarkably linear MR. Its enormous magnitude and weak temperature dependence indicate that this is a classical effect of disorder. In another study, we examine a specially designed dual-gated device that can induce low number density in a periodic pattern. By applying appropriate gate voltages, we demonstrate the formation of an electrostatically tunable quantum dot lattice and study the impact of disorder on it. This work is important in paving way for solid state based platform for experimental simulations of artificial solids.
The most striking property of bilayer graphene is the ability to open its band gap by a perpendicular electric field, giving the prospects of enabling a large set of de-vice applications. However, despite a band gap, a number of transport mechanisms are still active at very low densities that range from hopping transport through bulk to topologically protected 1D transport at the edges or along 1D crystal dislocations. In the second half of the thesis, we have used higher order statistical moment of resistance/conductance fluctuations, namely the variance of the fluctuations, to complement averaged resistance/conductance, and study and infer the dominant transport mechanism at low densities in a gapped bilayer graphene. Our results show possible evidence of percolative transport and topologically protected edge transport at different ranges of low number densities. We also explore the same phase space by studying its mesoscopic conductance fluctuations at very low temperatures. This is the first of its kind systematic experiment in a dual-gated bilayer graphene device. Its conductance fluctuations have several anomalous features suggesting non-universal behaviour which is at odds with conventional disordered systems.
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Zschornak, Matthias. "Defect-induced local electronic structure modifications within the system SrO - SrTiO3 - TiO2: symmetry and disorder". Doctoral thesis, 2014. https://tubaf.qucosa.de/id/qucosa%3A22987.
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Owing to their versatile orbital character with both local and highly dispersive degrees of freedom, transition metal oxides span the range of ionic, covalent and metallic bonding. They exhibit a vast diversity of electronic phenomena such as high dielectric, piezoelectric, pyroelectric, ferroelectric, magnetic, multiferroic, catalytic, redox, and superconductive properties. The nature of these properties arises from sensitive details in the electronic structure, e.g. orbital mixing and orbital hybridization, due to non-stoichiometry, atomic displacements, broken symmetries etc., and their coupling with external perturbations.
In the work presented here, these variations of the electronic structure of crystals due to structural and electronic defects have been investigated, exemplarily for the quasi-binary system SrO - SrTiO3 - TiO2. A number of binary and ternary structures have been studied, both experimentally as well as by means of electronic modeling. The applied methods comprise Resonant X-ray Scattering techniques like Diffraction Anomalous Fine Structure, Anisotropy of Anomalous Scattering and X-ray Absorption Fine Structure, and simultaneously extensive electronic calculations by means of Density Functional Theory and Finite Difference Method Near-Edge Structure to gain a thorough physical understanding of the underlying processes, interactions and dynamics.
It is analyzed in detail how compositional variations, e.g. manifesting as oxygen vacancies or ordered stacking faults, alter the short-range order and affect the electronic structure, and how the severe changes in mechanical, optical, electrical as well as electrochemical properties evolve. Various symmetry-property relations have been concluded and interpreted on the basis of these modifications in electronic structure for the orbital structure in rutile TiO2, for distorted TiO6 octahedra and related switching mechanisms of the Ti valence, for elasticity and resistivity in strontium titanate, and for surface relaxations in Ruddlesden-Popper phases.
Highlights of the thesis include in particular the methodical development regarding Resonant X-Ray Diffraction, such as the first use of partially forbidden reflections to get the complete phase information not only of the tensorial structure factor but of each individual atomic scattering tensor for a whole spectrum of energies, as well as the determination of orbital degrees of freedom and details of the partial local density of states from these tensors.
On the material side, the most prominent results are the identification of the migration-induced field-stabilized polar phase and the exergonic redox behavior in SrTiO3 caused by defect migration and defect separation.
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Lagerquist, Olle. "Neuromuscular electrical stimulation and the central nervous system". Phd thesis, 2009. http://hdl.handle.net/10048/537.
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Thesis (Ph.D.)--University of Alberta, 2009.A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Faculty of Physical Education and Recreation, Center for Neuroscience. Title from pdf file main screen (viewed on September 17, 2009). Includes bibliographical references.
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(10724028), Jason David Ummel. "NONINVASIVE MEASUREMENT OF HEARTRATE, RESPIRATORY RATE, AND BLOOD OXYGENATION THROUGH WEARABLE DEVICES". Thesis, 2021.
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The last two decades have shown a boom in the field of wearable sensing technology. Particularly in the consumer industry, growing trends towards personalized health have pushed new devices to report many vital signs, with a demand for high accuracy and reliability. The most common technique used to gather these vitals is photoplethysmography or PPG. PPG devices are ideal for wearable applications as they are simple, power-efficient, and can be implemented on almost any area of the body. Traditionally PPGs were utilized for capturing just heart rate, however, recent advancements in hardware and digital processing have led to other metrics including respiratory rate (RR) and peripheral oxygen saturation (SpO2), to be reported as well. Our research investigates the potential for wearable devices to be used for outpatient apnea monitoring, and particularly the ability to detect opioid misuse resulting in respiratory depression. Ultimately, the long-term goal of this work is to develop a wearable device that can be used in the rehabilitation process to ensure both accountability and safety of the wearer. This document details contributions towards this goal through the design, development, and evaluation of a device called “Kick Ring”. Primarily, we investigate the ability of Kick Ring to record heartrate (HR), RR, and SpO2. Moreover, we show that the device can calculate RR in real time and can provide an immediate indication of abnormal events such as respiratory depression. Finally, we explore a novel method for reporting apnea events through the use of several PPG characteristics. Kick Ring reliably gathers respiratory metrics and offers a combination of features that does not exist in the current wearables space. These advancements will help to move the field forward, and eventually aid in early detection of life-threatening events.