To see the other types of publications on this topic, follow the link: Highly correlated electrons.
Dissertations / Theses on the topic 'Highly correlated electrons'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 35 dissertations / theses for your research on the topic 'Highly correlated electrons.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Macarie, Liliana Sandina. "Correlated electrons and high-temperature superconductivity." Thesis, University of Warwick, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307992.
Full text
2
Alfonsov, Alexey. "High-field electron spin resonance study of electronic inhomogeneities in correlated transition metal compounds." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-74492.
Full textAbstract:
Electronic inhomogeneities play an important role in the definition of physical properties of correlated systems. To study these inhomogeneities one has to use local probe techniques which can distinguish electronic, magnetic and structural variations at the nanoscale. In the present work the high-field electron spin resonance technique (HF-ESR) is used to probe electronic and magnetic inhomogeneities in two transition-metal element based systems with very different properties. The first system is an iron based hightemperature superconductor, namely a member of a so called 1111-family, the (La,Gd)O1−xFxFeAs compound. Our HF-ESR spectroscopy study on Gd3+ ion has revealed that this material exhibits anisotropic interaction between Gd and Fe layers, which is frustrated in the absence of an external magnetic field. Moreover, the study of the superconducting samples has shown a coexistence of a static short range magnetic order with superconductivity up to high doping levels. The second system is a lightly hole doped cubic perovskite LaCoO3. Here, our HF-ESR investigation, complemented with static magnetometry and nuclear magnetic resonance techniques, has established that the hole doping induces a strong interaction between electrons on neighboring Co ions which leads to a collective high-spin state, called a spin-state polaron. These polarons are inhomogeneously distributed in the nonmagnetic matrix.
This thesis is organized in three chapters. The first chapter gives basic ideas of magnetism in solids, focusing on the localized picture. The aim of the second chapter is to introduce the method of ESR. The third chapter is dedicated to the study of 1111-type iron arsenide superconductors. In the first part X-band (9.5 GHz) ESR measurements on 2% and 5% Gd-doped LaO1−xFxFeAs are presented. In the second part a combined investigation of the properties of GdO1−xFxFeAs samples by means of thermodynamic, transport and high-field electron spin resonance methods is presented. The last, fourth chapter presents the investigation of the unexpected magnetic properties of lightly hole-doped LaCoO3 cobaltite by means of the electron spin resonance technique complemented by magnetization and nuclear magnetic resonance measurements.
3
Ruiz-Tijerina, David A. "Kondo Physics and Many-Body Effects in Quantum Dots and Molecular Junctions." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1385982088.
Full text
4
Ghazi, Mohammad Ebrahim. "High-resolution X-ray scattering studies of charge ordering in highly correlated electron systems." Thesis, Durham University, 2002. http://etheses.dur.ac.uk/3869/.
Full textAbstract:
Many important properties of transition metal oxides such as, copper oxide high- temperature superconductivity and colossal magnetoresistance (CMR) in manganites are due to strong electron-electron interactions, and hence these systems are called highly correlated systems. These materials are characterised by the coexistence of different kinds of order, including charge, orbital, and magnetic moment. This thesis contains high-resolution X-ray scattering studies of charge ordering in such systems namely the high-T(_c) copper oxides isostructural system, La(_2-x)Sr(_x)NiO(_4)) with various Sr concentrations (x = 0.33 - 0.2), and the CMR manganite system, Nd(_1/2)Sr(_1/2)MnO(_3)). It also includes a review of charge ordering in a large variety of transition metal oxides, such as ferrates, vanadates, cobaltates, nickelates, manganites, and cuprates systems, which have been reported to date in the scientific literature. Using high-resolution synchrotron X-ray scattering, it has been demonstrated that the charge stripes exist in a series of single crystals of La(_2-x)Sr(_x)NiO(_4)) with Sr concentrations (x = 0.33 - 0.2) at low temperatures. Satellite reflections due to the charge ordering were found with the wavevector (2Ɛ, 0, 1) below the charge ordering transition temperature, Tco, where 2 Ɛ is the amount of separation from the corresponding Bragg peak. The charge stripes are shown to be two-dimensional in nature both by measurements of their correlation lengths and by measurement of the critical exponents of the charge stripe melting transition with an anomaly at x = 0.25. The results show by decreasing the hole concentration from the x = 0.33 to 0.2, the well-correlated charge stripes change to a glassy state at x = 0.25. The electronic transition into the charge stripe phase is second-order without any corresponding structural transition. Above the second-order transition critical scattering was observed due to fluctuations into the charge stripe phase. In a single-crystal of Nd(_1/2)Sr(_1/2)MnO(_3) a series of phase transitions were observed using high-resolution synchrotron X-ray scattering. Above the charge ordering transition temperature, Tco, by measuring the peak profiles of Bragg reflections as a function of temperature, it was found that this crystal undergoes two transitions corresponding to the transition from a paramagnetic- to a ferromagnetic state at T ≈ 252 K, and the formation of a mixture of the antiferromagnetic and ferromagnetic phases below T ≈ 200 K. Below the charge ordering temperature, Tco =162 K, additional satellite reflections with the wavevector, q = (1/2, 0, 0), were observed due to Jahn-Teller distortion of the MnO(_6) octahedra caused by charge- and orbital ordering in sample. This transition was observed to be of first-order with a hysteresis width of 10 K. In addition, another very weak satellites with wavevector (1/2, 1, 1/2) were observed possibly due to spin ordering.
5
Cricchio, Francesco. "Multipoles in Correlated Electron Materials." Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132068.
Full textAbstract:
Electronic structure calculations constitute a valuable tool to predict the properties of materials. In this study we propose an efficient scheme to study correlated electron systems with essentially only one free parameter, the screening length of the Coulomb potential. A general reformulation of the exchange energy of the correlated electron shell is combined with this method in order to analyze the calculations. The results are interpreted in terms of different polarization channels, due to different multipoles. The method is applied to various actinide compounds, in order to increase the understanding of the complicate behaviour of 5f electrons in these systems. We studied the non-magnetic phase of δ-Pu, where the spin polarization is taken over by a spin-orbit-like term that does not break the time reversal symmetry. We also find that a non-trivial high multipole of the magnetization density, the triakontadipole, constitutes the ordering parameter in the mysterious hidden order phase of the heavy-fermion superconductor URu2Si2. This type of multipolar ordering is also found to play an essential role in the hexagonal-based superconductors UPd2Al3, UNi2Al3 and UPt3 and in the dioxide insulators UO2, NpO2 and PuO2. The triakontadipole moments are also present in all magnetic actinides we considered, except for Cm. These results led us to formulate a new set of rules for the ground state of a system, that are valid in presence of strong spin-orbit coupling interaction instead of those of Hund; the Katt's rules. Finally, we applied our method to a new class of high-Tc superconductors, the Fe-pnictides, where the Fe 3d electrons are moderately correlated. In these materials we obtain the stabilization of a low spin moment solution, in agreement with experiment, over a large moment solution, due to the gain in exchange energy in the formation of large multipoles of the spin magnetization density.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 705
6
Sica, G. "Electron-electron and electron-phonon interactions in strongly correlated systems." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12194.
Full textAbstract:
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.
7
Chapman, James R. "Optical properties of highly correlated electron systems in a magnetic field." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389008.
Full text
8
Beebe, Melissa R. "Highly-Correlated Electron Behavior in Niobium and Niobium Compound Thin Films." W&M ScholarWorks, 2017. https://scholarworks.wm.edu/etd/1499450045.
Full textAbstract:
Electron correlations are the root of many interesting phenomena in materials, including phase transitions such as superconductivity and insulator-to-metal transitions, which are of great interest both for scientific understanding and for many applications. Such phase transitions can often be tailored in thin films, in which the geometry of the material is limited in one dimension. By studying how the physical structure of a thin film affects its correlated electron response, it is possible to obtain useful insight into both the nature of the electron correlations present in the material and how to control them for various applications. Niobium, an elemental superconductor, has the highest critical temperature and lower critical field of the naturally-occurring superconductors, making it attractive for many applications, particularly in the superconducting radio frequency (SRF) community. Several niobium-based compounds are also superconductors of interest; while the bulk materials are fairly well-understood, there is still a great deal to learn regarding the effects of the microstructure of thin films of these materials on their superconducting properties. Another niobium compound, niobium dioxide, exhibits a phase transition from a room-temperature insulating state to a high-temperature metallic state. Such insulator-to-metal transitions are not well-understood, even in bulk, and there is a great deal of debate over the mechanism that drives them. Experimental studies on niobium dioxide thin films are still somewhat rare and thus have the potential to contribute a great deal to the understanding of the mechanisms behind the transition. This dissertation presents structure-property correlation studies on niobium and niobium compound superconducting thin films such as those discussed above, and also reports on the first experimental studies of the light-induced insulator-to-metal transition in niobium dioxide.
9
Chernenkaya, Alisa [Verfasser]. "Electronic structure of highly-correlated low-dimensional organic conductors / Alisa Chernenkaya." Mainz : Universitätsbibliothek Mainz, 2017. http://d-nb.info/1134993609/34.
Full text
10
Elbahrawy, Mohammed. "High field electron magnetic resonance in complex correlated spin systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-39380.
Full textAbstract:
In this thesis we used ESR to investigate magnetic properties of low D vandium and copper oxides in which small quantum spins are arranged in 1D chains and 2D layers. The thesis covers five different low dimensional spin systems. They turned out to be experimental reliazation of some of the most intersiting theoritical models in the field of quantum magnetism.
11
Edwards, Rachel Sian. "GHz measurements of correlated electron systems in high magnetic fields." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249567.
Full text
12
Haines, Charles Robert Sebastian. "Pressure tuned magnetism in d- and f-electron materials." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/282990.
Full textAbstract:
Quantum phase transitions (QPT) on the border of magnetism have provided a fertile hunting ground for the discovery of new states of matter, for example; the marginal Fermi Liquid and non Fermi Liquid states as well high T$_C$ cuprate and magnetically mediated superconductivity. In this thesis I present work on three materials in which it may be possible to tune the system through a magnetic QPT with the application of hydrostatic pressure. Although the details of the underlying physics are different in each of the materials, they are linked by the possibility of finding new states on the border of magnetism. Applying hydrostatic pressure, we have suppressed the ferromagnetic (FM) transition in metallic Fe$_2$P to very low temperature and to a potential QPT. Counter-intuitive broadening of the magnetic hysteresis leading up to the FM-AFM QPT may well be a crucial clue as to the nature of the model needed to understand this phase transition. A sharp increase in the quasi-particle scattering cross-section as well as the residual resistivity accompany a departure from the quadratic temperature dependence of the resistivity. This possible deviation from Fermi liquid behaviour is stable over a significant range of temperature. The unexplained upturn in the resistivity of CeGe that accompanies the AFM transition was studied under pressure. Pressure increased the residual resistivity as well as decreasing the relative size of the upturn, but had a moderate effect on the Neel temperature. The insensitivity of the N$\acute e$el temperature to pressure has been compared to its relative sensitivity to applied feld. The existence of the upturn and its evolution with pressure and applied feld can reasonably be argued to be due to the details of the electron band structure in the system. By applying pressure we have drastically reduced the resistivity of the insulating antiferromagnet NiPS$_3$. Concurrent work on FePS$_3$ has shown metallisation under pressure. It seems reasonable to speculate that NiPS$_3$ may also metallise at higher pressure. The energy gap is narrowed in both materials as pressure is increased. Magnetisation measurements have revealed a low temperature upturn indicating some possible ferromagnetic component or proximity to another magnetic state. A peak in the magnetisation is also seen at 45K in zero-feld cooled measurements. Both of these features point to a system with a complex magnetic ground state.
13
Alfonsov, Alexey [Verfasser], Bernd [Akademischer Betreuer] Büchner, and Rüdiger [Akademischer Betreuer] Klingeler. "High-field electron spin resonance study of electronic inhomogeneities in correlated transition metal compounds / Alexey Alfonsov. Gutachter: Bernd Büchner ; Rüdiger Klingeler. Betreuer: Bernd Büchner." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://d-nb.info/1067190694/34.
Full text
14
Weller, Matthias. "NMR NQR studies at very low temperatures and high pressures in strongly correlated electron systems." kostenfrei, 2007. http://e-collection.ethbib.ethz.ch/view/eth:30167.
Full text
15
Zegkinoglou, Ioannis. "Resonant and high energy X-ray scattering studies on strongly correlated electron systems in transition metal oxides." [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-30539.
Full text
16
Kim, Timur K. "The role of inter-plane interaction in the electronic structure of high Tc cuprates." Doctoral thesis, [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971334706.
Full text
17
Kim, Timur K. "The role of inter-plane interaction in the electronic structure of high Tc cuprates." Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24337.
Full textAbstract:
This thesis represents a systematic study of electronic structure of the modulation-free Pb-doped Bi2212 superconducting cuprates with respect to interlayer coupling done by using the angle-resolved photoemission spectroscopy (ARPES), which is a leading technique in the experimental investigation of the single particle excitations in solids. The results presented in this work indicate a very different origin for the observed complex spectra lineshape. Specifically, the peak-dip-hump lineshape can be easily understood in terms of the superposition of spectral features due to bilayer band splitting, namely the splitting of the CuO2 plane derived electronic structure in bonding and antibonding bands due to the interlayer coupling of CuO2 bilayer blocks within the unit cell of Bi2212. By performing experiments at synchrotron beamlines where the energy of the incoming photons can be tuned over a very broad range, the detailed matrix elements energy dependence for both bonding and antibonding bands was determined. This gave the opportunity to study the electronic properties these two bands separately. For the first time, it was proved that the superconducting gap has the same value and symmetry for both bands. Furthermore, having recognized and sorted out the bilayer splitting effects, it became possible to identify more subtle effects hidden in the details of the ARPES lineshapes. On underdoped samples an "intrinsic" peak-dip-hump structure due to the interaction between electrons and a bosonic mode was observed. Studying the doping, temperature, and momentum dependence of the photoemission spectra it was established that: the mode has a characteristic energy of 38-40 meV and causes strong renormalization of the electronic structure only in the superconducting state; the electron-mode coupling is maximal around the (?à,0) point in momentum space and is strongly doping dependent (being greatly enhanced in the underdoped regime). From the above, it was concluded that the bosonic mode must correspond to the sharp magnetic resonance mode observed in inelastic neutron scattering experiments, and that this coupling is relevant to superconductivity and the pairing mechanism in the cuprates.
18
Park, Jaena [Verfasser], and Rüdiger [Akademischer Betreuer] Klingeler. "High-field Electron Spin Resonance study on Correlated Transition Metal Compounds and Metal-Organic Compounds / Jaena Park ; Betreuer: Rüdiger Klingeler." Heidelberg : Universitätsbibliothek Heidelberg, 2015. http://d-nb.info/1180608984/34.
Full text
19
Yu, Xinyu. "High-temperature Bulk CMOS Integrated Circuits for Data Acquisition." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1144420886.
Full text
20
Müller, Beate. "Beyond the common view of Bi cuprates." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16221.
Full textAbstract:
Die vorliegende Arbeit befasst sich mit der elektronischen Struktur von Bi-Kupraten vom Normalzustand bis in den supraleitenden Zustand. Der Normalzustand von einschichtigen Bi-Kupraten wurde mittels polarisationsabhängiger XAS untersucht. Es konnte eine deutliche Polarisationsabhängigkeit der CuL3- und OK-Kante innerhalb der Kupferoxidebene beobachtet werden. Insbesondere in den Merkmalen, die den dotierten Löchern zugeordnet werden. Die Winkelabhängigkeit geht über die erwartete Hybridisierung von Cu3dx^2-y^2- und O2px,y-Orbitalen hinaus, und unterstützt somit Theorien, die auch Orbitale ausserhalb der Kupferoxidebene zur Beschreibung der elektronischen Struktur einbeziehen. Desweiteren wurde beobachtet, dass die Ladungs-Transfer-Lücke sich mit steigender Lochkonzentration vergrößert konform zu Theorien zum Zusammenbruch der Zhang-Rice-Singuletts im überdotierten Bereich. Mittels ARPES wurden die Anregungen nahe der Fermikante in antinodaler Richtung an zweischichtigen Bi-Kupraten untersucht. Die komplexe Linienform im zweischichtigen Bi-Kuprat, die aus Interlageneffekten resultiert, wurde durch die gezielte Ausnutzung von Matrixelementeffekten vereinfacht. Dadurch konnten, in Kombination mit der spezifischen Ausrichtung der Polarisation, vorherige, sich scheinbar widersprechende Beobachtungen am einschichtigen und zweischichtigen Bi-Kuprat in Einklang gebracht werden. Es konnte gezeigt werden, dass im zweischichtigen Bi-Kuprat eine Anregung zusätzlich zum bindenden und antibindenden Band existiert, welche mit dem antibindenden Band korreliert zu sein scheint. Außerdem zeigt es Gemeinsamkeiten mit dem scharfen Peak, der im einschichtigen Bi-Kuprat gefunden wurde. So besteht es über die supraleitende Sprungtemperatur Tc hinaus, und verschwindet vermutlich bei oder über der Pseudolücken-Temperatur T*. Die ARPES Messungen lassen sich am Besten innerhalb des Modells elektronischer Inhomogenitäten erklären, welches Hochtemperatursupraleitung aus Streifen ableitet.The electronic structure of Bi cuprates from the normal state down to the superconducting state has been investigated. The normal state electronic structure is probed by polarization dependent XAS on single layer Bi cuprates. With the x-ray beam being incident normal to the CuO2 plane the azimuthal angle was varied to explore the polarization effects on orbitals within the plane. In the CuL3- as well as the OK-edge spectra, the spectral features related to the doped holes showed a distinct polarization dependence within the CuO2 plane. The revealed polarization dependence is more complex than expected from hybridization of Cu3dx^2-y^2 and O2px,y orbitals only. Thus, the results support the inclusion of out-of-plane orbitals into the description of the electronic structure as has been previously theoretically proposed. Furthermore, the charge transfer gap has been observed to rise with rising hole concentration supporting theories of the instability of Zhang-Rice-singlets in the overdoped regime. By ARPES the excitations close to the Fermi surface in the antinodal region of double layer Bi cuprates have been investigated. The complex lineshape in double layer Bi cuprates that results from interlayer effects has been disentangled by exploiting matrix element effects. In combination with distinct polarization settings this enabled to unify seemingly inconsistent observations made on single and double layer Bi cuprates. The existence of an excitation additional to antibonding and bonding band could be shown in the double layer Bi cuprate. This additional excitation is probably connected to the antibonding band. It furthermore shows similarities to the sharp peak observed in single layer Bi cuprates. It persists to temperatures above the superconducting temperature Tc, and presumably vanishes at or above the pseudogap temperature T*. The ARPES results could be best explained within the model of electronic inhomogeneity which derives superconductivity from stripes.
21
Qiu, Lei. "Exploring 2D Metal-Insulator Transition in p-GaAs Quantum Well with High rs." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1386337954.
Full text
22
Romain, Vasseur. "Indecomposabilité dans les théories des champs et applications aux systèmes désordonnés et aux problèmes géométriques." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00876155.
Full textAbstract:
Les théories des champs conformes logarithmiques (LCFTs) sont cruciales pour décrire le comportement critique de systèmes physiques variés: les transitions de phase dans les systèmes électroniques désordonnés sans interaction (comme par exemple la transition entre plateaux dans l'effet Hall quantique entier), les points critiques désordonnés dans les systèmes statistiques classiques (comme le modèle d'Ising avec liens aléatoires), ou encore les modèles géométriques critiques (comme la percolation ou les marches aléatoires auto-évitantes). Les LCFTs décrivent des théories non unitaires, qui ne seraient probablement pas pertinentes dans le contexte de la physique des particules, mais qui apparaissent naturellement en matière condensée et en physique statistique. Sans cette condition d'unitarité, toute la puissance algébrique qui a fait le succès des théories conformes est fortement compromise à cause de ''l'indécomposabilité'' de la théorie des représentations sous-jacente. Ceci a pour conséquence de modifier les fonctions de corrélation algébriques par des corrections logarithmiques, et réduit sévèrement l'espoir d'une classification générale. Le but de cette thèse est d'analyser ces théories logarithmiques en étudiant leur régularisation sur réseau, l'idée principale étant que la plupart des difficultés algébriques causées par l'indécomposabilité sont déjà présentes dans des systèmes de taille finie. Notre approche consiste à considérer des modèles statistiques critiques avec matrice de transfert non diagonalisable (ou des chaînes de spins critiques avec Hamiltonien non diagonalisable) et d'analyser leur limite thermodynamique à l'aide de différentes méthodes numériques, algébriques et analytiques. On explique en particulier comment mesurer numériquement les paramètres universels qui caractérisent les représentations indécomposables qui apparaissent à la limite continue. L'analyse détaillée d'une vaste classe de modèles sur réseau nous permet également de conjecturer une classification de toutes les LCFTs chirales pertinentes physiquement, pour lesquelles la seule symétrie est donnée par l'algèbre de Virasoro. Cette approche est aussi partiellement étendue aux théories non chirales, avec une attention particulière portée au problème bien connu de la formulation d'une théorie des champs cohérente qui décrirait la percolation en deux dimensions. On montre que les modèles sur réseaux périodiques ou avec bords peuvent être reliés algébriquement seulement dans le cas des modèles minimaux, impliquant des conséquences intéressantes pour les théories des champs sous-jacentes. Un certain nombre d'applications aux systèmes désordonnés et aux modèles géométriques sont également abordées, avec en particulier une discussion détaillée des observables avec comportement logarithmique au point critique dans le modèle de Potts en dimension arbitraire.
23
Säll, Erik. "Design of a Low Power, High Performance Track-and-Hold Circuit in a 0.18µm CMOS Technology." Thesis, Linköping University, Department of Electrical Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-1353.
Full textAbstract:
This master thesis describes the design of a track-and-hold (T&H) circuit with 10bit resolution, 80MS/s and 30MHz bandwidth. It is designed in a 0.18µm CMOS process with a supply voltage of 1.8 Volt. The circuit is supposed to work together with a 10bit pipelined analog to digital converter.
A switched capacitor topology is used for the T&H circuit and the amplifier is a folded cascode OTA with regulated cascode. The switches used are of transmission gate type.
The thesis presents the design decisions, design phase and the theory needed to understand the design decisions and the considerations in the design phase.
The results are based on circuit level SPICE simulations in Cadence with foundry provided BSIM3 transistor models. They show that the circuit has 10bit resolution and 7.6mW power consumption, for the worst-case frequency of 30MHz. The requirements on the dynamic performance are all fulfilled, most of them with large margins.
24
Texier, Yoan. "Diagramme de phase et corrélations électroniques dans les supraconducteurs à base de Fer : une étude par RMN." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00869743.
Full textAbstract:
La découverte en 2008 de supraconductivité à relativement haute température (Tc,max = 56K) dans les pnictures de Fer a ravivé les questions fondamentales sur l'origine et la nature de la supraconductivité posés par les supraconducteurs non conventionnels. En particulier, la présence d'une phase antiferromagnétique à proximité de celle supraconductrice dans leur diagramme de phase pose la question du lien entre magnétisme et supraconductivité. Ces supraconducteurs à base de Fe présentent un diagramme de phase générique, mais quelques exceptions remettent en question une description qui se voudrait universelle. Nous avons choisi d'étudier ces cas particuliers grâce à une sonde locale, la résonance magnétique nucléaire (RMN). Nos observations nous ont non seulement permis de comprendre la raison de ces exceptions, mais aussi de s'en servir pour mieux sonder les corrélations magnétiques dans ces matériaux, un ingrédient clé pour la compréhension de la supraconductivité. Premier sujet, la coexistence de supraconductivité et de magnétisme : celle-ci a été observée dans la plupart des supraconducteurs à base de Fer de façon homogène ou inhomogène, mais toujours pour des états magnétiques à faible TN et faibles moments en accord avec des descriptions itinérantes à faibles corrélations. Pourtant un nouveau composé au Sélénium est venu remettre en cause ces conclusions en présentant une apparente coexistence homogène entre une forte supraconductivité macroscopique (Tc ≈ 30K) et un très fort antiferromagnétisme (TN ≈ 600K, moments magnétiques de valeur élevée de 3.3µB). Cette observation suggère donc une description ici plutôt en terme d'isolants de Mott contrairement aux autres supraconducteurs à base de Fer. Nos mesures RMN permettent de montrer en fait l'existence d'une séparation de phase et de statuer sur la stœchiométrie et les propriétés électroniques des différentes phases, pour finalement réconcilier ce composé et les autres familles. Deuxième exception : dans la famille archétype BaFe₂As₂, tous les dopages sur site Fer ou Arsenic ou même l'application de pression mènent à la supraconductivité, sauf dans le cas du dopage au Manganèse ou au Chrome en site Fer, qui ne provoquent pas l'apparition de la supraconductivité. Nos mesures RMN nous ont permis de sonder la nature de la transition magnétique, mais aussi l'état métallique de ces composés substitués. Nous montrons en particulier que le trou supplémentaire du Manganèse substitué à la place du Fer reste en fait localisé sur son site et se manifeste alors par un moment magnétique localisé. Cette étude du dopage par le Manganèse ouvre la voie à l'idée d'utiliser le Manganèse en faible concentration comme source de moments localisés qui polarisent magnétiquement leur environnement. Cette polarisation permet en effet de caractériser la nature même des corrélations de spin. Nous avons donc utilisé la RMN ainsi que la magnétométrie-SQUID pour mesurer cette polarisation dans des composés supraconducteurs pour sonder les corrélations de spins de ces systèmes. Nous concluons que ces corrélations sont plutôt faibles et indépendantes de la température dans les composés dopés en électrons.
25
Shevchenko, Pavel V. "Quantum phenomena in strongly correlated electron systems /." 1999. http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-NUN20001116.154442/index.html.
Full text
26
Johnston, Steven Sinclair. "Electron-phonon Coupling in Quasi-Two-Dimensional Correlated Systems." Thesis, 2010. http://hdl.handle.net/10012/5274.
Full textAbstract:
Over the past 20 years a great deal of progress has been made towards understanding the physics of the high-temperature (high-Tc) cuprate superconductors. Much of the low- energy physics of these materials appears to be captured by two-dimensional Hubbard or t-J models which have provided significant insight into a number of properties such as the pseudogap, antiferromagnetism and superconductivity itself. However, intrinsically planar models are unable to account for the large variations in Tc observed across materials nor do they capture the electron-phonon (el-ph) interaction, the importance of which a number of experimental probes now indicate.
This thesis examines the el-ph interaction in cuprates using a combination of analytical and numerical techniques. Starting from the microscopic mechanism for coupling to in-plane and c-axis polarized oxygen phonons, the theory of el-ph coupling is presented. The el-ph self-energy is derived in the context of Migdal-Eliashberg theory and then applied to understanding the detailed temperature and doping dependence of the renormalizations observed by Angle-resolved photoemission spectroscopy. The qualitative signatures of el- boson coupling in the density of states of a d-wave superconductor are also examined on general grounds and a model calculation is presented for el-ph coupling signatures in the density of states. Following this, the theory is extended to include the effects of screening and the consequences of this theory are explored. Due to the quasi-2D nature of the cuprates, screening is found to anomalously enhance the el-ph contribution to d-wave pairing. This result is then considered in light of the material and doping dependence of Tc and a framework for understanding the materials variations in Tc is presented. From these studies, a detailed picture of the role of the el-ph interaction in the doped cuprates emerges where the interaction, working in conjunction with a dominant pairing interaction, provides much of the materials variations in Tc observed across the cuprate families.
Turning towards numerical techniques, small cluster calculations are presented which examine the effects of a local oxygen dopant in an otherwise ideal Bi2Sr2CaCu2O8+δ crystal. Here, it is demonstrated that the dopant locally enhances electronic properties such as the antiferromagnetic exchange energy J via local el-ph coupling to planar local oxygen vibrations. Finally, in an effort to extend the scope of this work to the underdoped region of the phase diagram, an examination of the properties of the single-band Hubbard and Hubbard-Holstein model is carried out using Determinant Quantum Monte Carlo. Here focus is placed on the spectral properties of the model as well as the competition between the the antiferromagnetic and charge-density-wave orders. As with the small cluster calculations, a strong interplay between the magnetic and lattice properties is observed.
27
Zhou, Wenduo. "Monte Carlo summation of higher order Feynman diagram expansions for strongly correlated electron models." 2006. http://purl.galileo.usg.edu/uga%5Fetd/zhou%5Fwenduo%5F200608%5Fphd.
Full text
28
Richter, Felix [Verfasser]. "Theory of radiation for bounded media systems with highly correlated electron-hole plasmas / vorgelegt von Felix Richter." 2009. http://d-nb.info/1003039928/34.
Full text
29
Gupta, Subhra Sen. "Theoretical Investigations Of Core-Level Spectroscopies In Strongly Correlated Systems." Thesis, 2006. http://hdl.handle.net/2005/421.
Full textAbstract:
Ever since the discovery of exotic phenomena like high temperature (Tc) superconductivity
in the cuprates and colossal magnetoresistance in the manganites, strongly correlated electron systems have become the center of attention in the field of condensed matter physics research. This renewed interest has been further kindled by the rapid development of sophisticated experimental techniques and tremendous computational power. Computation plays
a pivotal role in the theoretical investigation of these systems, because one cannot explain their complicated phase diagrams by simple, exactly solvable models. Among the plethora of experimental techniques, various kinds of high energy electron spectroscopies are fast gaining importance due to the multitude of physical properties and phenomena which they
can access. However the physical processes involved and the interpretation of the spectra obtained from these spectroscopies are extremely complex and require extensive theoretical modelling. This thesis is concerned with the theoretical modelling of a certain class of high energy electron spectroscopies, viz. the core-level electron spectroscopies, for strongly correlated systems of various kinds. The spectroscopies covered are Auger electron spectroscopy
(AES), core-level photoemission spectroscopy (core-level PES) and X-ray absorption spec-
troscopy (XAS), which provide non-magnetic information, and also X-ray magnetic circular
and linear dichroism (XMCD and XMLD), which provide magnetic information.
.
30
Han, Fuxiang. "Coexistance of spin and charge density fluctuations in strongly correlated systems." Thesis, 1993. http://hdl.handle.net/1957/35825.
Full textAbstract:
Spin and charge density fluctuations are important excitations in the strongly correlated systems, especially in the recently discovered high temperature superconductors. Several different theories on high temperature superconductors have been proposed based on spin fluctuations. However, experiments have also shown the existence of strong charge fluctuations. It is, therefore, desirable to investigate the physical consequences of the coexistence of strong spin and charge density fluctuations. As a first step toward a full understanding of both spin and charge excitations, a self-consistent theory is established. In this self-consistent theory, there are three important quantities, the spin susceptibility, the charge susceptibility, and the phonon Green's function. These three quantities are coupled together by the electron-phonon and phonon-spin fluctuation interactions. The phonon-spin fluctuation interaction is derived by making use of the spin-orbital coupling.
For a strongly correlated system, the spin and charge density excitations have to be considered self-consistently. They are intimately related.
The effects of antiparamagnons on phonons are also investigated. Antiparamagnons can have dramatic effects on phononic properties. It is found that new modes are formed in the presence of antiferromagnetic spin fluctuations.
The de Haas-van Alphen effect in marginal and nearly antiferromagnetic Fermi liquids is studied. It is found that the de Haas-van Alphen frequency is unaffected by the anomalous response functions of the marginal and nearly antiferromagnetic Fermi liquids due to the absence of real parts of self-energies on the imaginary frequency axis.Graduation date: 1993
31
Elbahrawy, Mohammed Yehia Taha Ahmed [Verfasser]. "High field electron magnetic resonance in complex correlated spin systems / von Mohammed Yehia Taha Ahmed Elbahrawy." 2010. http://d-nb.info/1008110426/34.
Full text
32
Zegkinoglou, Ioannis [Verfasser]. "Resonant and high-energy X-ray scattering studies on strongly correlated electron systems in transition metal oxides / vorgelegt von Ioannis Zegkinoglou." 2007. http://d-nb.info/98408469X/34.
Full text
33
Rourke, Patrick Michael Carl. "Electronic States of Heavy Fermion Metals in High Magnetic Fields." Thesis, 2009. http://hdl.handle.net/1807/17825.
Full textAbstract:
Heavy fermion metals often exhibit novel electronic states at low temperatures, due to competing interactions and energy scales. In order to characterize these states, precise determination of material electronic properties, such as the Fermi surface topology, is necessary. Magnetic field is a particularly powerful tool, since it can be used as both a tuning parameter and probe of the fundamental physics of heavy fermion compounds.
In CePb3, I measured magnetoresistance and torque for 23 mK ≤ T ≤ 400 mK, 0 T ≤ H ≤ 18 T, and magnetic field rotated between the (100), (110), and (111) directions. For H||(111), my magnetoresistance results show a decreasing Fermi liquid temperature range near Hc, and a T^2 coefficient that diverges as A(H) ∝ |H −Hc|^−α, with Hc ~ 6 T and α ~ 1. The torque exhibits a complicated dependence on magnetic field strength and angle. By comparison to numerical spin models, I find that the “spin-flop” scenario previously thought to describe the physics of CePb3 does not provide a good explanation of the experimental results.
Using novel data acquisition software that exceeds the capabilities of a traditional measurement set-up, I measured de Haas–van Alphen oscillations in YbRh2Si2 for 30 mK ≤ T ≤ 600 mK, 8 T ≤ H ≤ 16 T, and magnetic field rotated between the (100), (110), and (001) directions. The measured frequencies smoothly increase as the field is decreased through H0 ≈ 10 T. I compared my measurements to 4f-itinerant and 4f-localized electronic structure calculations, using a new algorithm for extracting quantum oscillation information from calculated band energies, and conclude that the Yb 4f quasi-hole remains itinerant over the entire measured field range, with the behaviour at H0 caused by a Fermi surface Lifshitz transition. My measurements are the first to directly track the Fermi surface of YbRh2Si2 across this field range, and rule out the 4f localization transition/crossover that was previously proposed to occur at H0.
34
蔣永勝. "The correlated study of the industry students of electronic department in senior industrial vocational high schools toward the career planning and skill-learning motivation." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/09212832683915819351.
Full textAbstract:
碩士國立彰化師範大學
工業教育與技術學系
93
The major purpose of this study is to explore the issues of the electrical engineering department students in vocational high school toward the Students Career Planning in the central area of Taiwan. To achieve the purpose, the correlation of skill- learning motivation was reviewed and analyzed as the framework of this study. The research adopted a questionnaire survey to collect empirical data. 1034 electrical engineering department students were chosen as objects and they came from 13 different schools, including vocational, agricultural, commercial high schools in a stratified random sampling way from the central area in Taiwan. The total valid questionnaires were 704, because only 840 out of 1034 questionnaires were returned and 136 were invalid. The validity rate was about 84%. The data of these valid questionnaires were analyzed with the methods of the descriptive statistics, t-test and one-way ANOVA. According to the results and suggests of the questionnaire analysis, findings could be seen: Ⅰ、Conclusions 1. There was no significant difference among careering feeling, career belief, and career plan for different grade students in the department of electrical. 2. Students in the department of electrical engineering in different types of schools have no obvious difference from another on behavior of skill-learning motivation. However, there are significant difference among the other orientations: cognitive、humanistic、controlled-meaning、learning-achievement and social-learning. It is found that the skill-learning motivation of vocational school is higher than commercial and agricultural school, and agricultural school is higher than commercial school. 3. There are positive correlations between control belief in skill-learning motivation and career planning for students in the department of electrical engineering.
35
Hershberg, Benjamin Poris. "Ring amplification for switched capacitor circuits." Thesis, 2012. http://hdl.handle.net/1957/31112.
Full textAbstract:
A comprehensive and scalable solution for high-performance switched capacitor amplification is presented. Central to this discussion is the concept of ring amplification. A ring amplifier is a small modular amplifier derived from a ring oscillator that naturally embodies all the essential elements of scalability. It can amplify with accurate rail-to-rail output swing, drive large capacitive loads with extreme efficiency using slew-based charging, naturally scale in performance according to process trends, and is simple enough to be quickly constructed from only a handful of inverters, capacitors, and switches. In addition, the gain-enhancement technique of Split-CLS is introduced, and used to extend the efficacy of ring amplifiers in specific and other amplifiers in general. Four different pipelined ADC designs are presented which explore the practical implementation options and design considerations relevant to ring amplification and Split-CLS, and are used to establish ring amplification as a new paradigm for scalable amplification.Graduation date: 2012
Access restricted to the OSU Community, at author's request, from July 19, 2012 - July 19, 2013