Dissertations / Theses on the topic 'Experimental condensed matter physics'
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Daniilidis, Nikolaos. "Experimental studies of the Bragg Glass transition in niobium." View abstract/electronic edition; access limited to Brown University users, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3318303.
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Varner, Samuel John. "Experimental and computational techniques in carbon-13 NMR." W&M ScholarWorks, 1999. https://scholarworks.wm.edu/etd/1539623952.
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An efficient method for calculating NMR lineshapes from anisotropic second rank tensor interactions is presented. The algorithm produces lineshapes from asymmetric tensors by summing those from symmetric tensors. This approach significantly reduces the calculation time, greatly facilitating iterative nonlinear least squares fitting of experimental spectra. This algorithm has been modified to produce partially relaxed lineshapes and spectra of partially ordered samples.;Calculations for rapidly spinning samples show that spin-lattice relaxation time ( T1Z ) anisotropy varies with the angle between the spinning axis and the external field. When the rate of molecular motion is in the extreme narrowing limit, measurement of T1Z anisotropies for two different values of the spinning angle allows the determination of two linear combinations of the three static spectral densities, J0(0), J1(0) and J2(0). Experimental results for ferrocene demonstrate the utility of these linear combinations in the investigation of molecular dynamics with natural abundance 13C NMR. For ferrocene-d 10, deuteron T1Z and quadrupolar order relaxation time ( T1Q ) anisotropies, along with the relaxation time of the 13C magic angle spinning (MAS) peak, provide sufficient information to determine the orientation dependence of all three individual spectral densities. The experimental results include the first determination of J 0(0) in a solid sample.;A variety of experimental techniques were used in an investigation of the polyimides LaRC-IA, LaRC-TPI and LaRC-SI and related model compounds. Magic angle spinning was used to acquire 13C isotropic chemical shift spectra of these materials. The spectra were assigned as completely as possible. In addition, the principal components of some shielding tensors were measured using variable angle correlation spectroscopy. of those studied, LaRC-SI is the only polymer that is soluble. However, after it is heated past its glass transition temperature, LaRC-SI becomes insoluble. Experiments were performed in an attempt to identify causes of this behavior. 1H and 13C NMR spectra of soluble and insoluble LaRC-SI are significantly different when magnetization from nuclei in rigid regions of the polymer is suppressed. Hydration studies of LaRC-SI and LaRC-IA show that absorbed water plasticizes these polymers.
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Xu, Yan 1963 Jan 31. "Experimental study of the structure of Ni-Zr metallic glasses." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41212.
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This thesis presents a structural study of Ni-Zr metallic glasses. It is the first time that a careful complete and systematic investigation into the structure of a glassy metallic system has been carried out. The results have improved our understanding of the structure of metallic glasses and clarified confusion in previous studies. The total structure factors of melt-spun and sputtered amorphous Ni$ sb{x}$Zr$ sb{1-x}$, 0.25 $ le$ x $ le$ 0.86, were obtained with an accuracy of 1-4%. Accurate partial structure factors of Ni$ sb{0.33}$Zr$ sb{0.67}$ and Ni$ sb{0.67}$Zr$ sb{0.33}$ were obtained using x-ray and neutron diffraction while those of Ni$ sb{0.33}$Zr$ sb{0.67}$ were also obtained independently using isomorphous substitution. The results confirmed the reliability of the isomorphous substitution method for Ni-Zr glasses. We have found a strong correlation between the local atomic structure and the electron transport properties of Ni-Zr glasses. No structural difference between melt-spun and sputtered Ni-Zr glasses was found. Our results show that the Faber-Ziman partial structure factors of Ni-Zr glasses is strongly composition dependent. The local topological order in amorphous Ni$ sb{0.33}$Zr$ sb{0.67}$ is found to be quite similar to that in the BCT NiZr$ sb2$ compound whereas a discrepancy in the structure is found between amorphous Ni$ sb{0.67}$Zr$ sb{0.33}$ and the FCC Ni$ sb2$Zr compound. Our results have also shown that the Ni-Zr glasses are an almost random mixture of Ni and Zr atoms and that there is no correlation between the pre-peak in the neutron structure factor and the chemical short-range order in the metallic glass.
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Giomi, Luca. "Unordinary order a theoretical, computational and experimental investigation of crystalline order in curved space /." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2009. http://wwwlib.umi.com/cr/syr/main.
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Kremeyer, Kevin P. 1968. "Experimental and computational investigations of binary solidification." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/289267.
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The topic of this dissertation is the solidification of a binary melt. The investigation is separated into three portions: An experimental investigation on the NH₄Cl--H₂O system; the development of a Cellular Automata code; and the development of a pair of coupled partial differential equations governing the evolution of an array of dendrites. Any necessary concepts are reviewed in the introduction. The experimental investigation focuses on the morphological transition from "slow" <100> dendrites to "fast" <111> dendrites. It is shown how the very complicated structures occurring during the transition actually have a simple explanation. The "slow-to-fast" transition has been previously investigated in the literature, and the relationships obtained in those studies can not account for the data collected in the present study. When "slow" dendrites are cooled into the "fast" regime, a curious stagnation of growth has also been observed. Additionally, two mechanisms are proposed as possible contributions to the order-of-magnitude jump in speed at the slow-to-fast transition. One mechanism is that of a "herringbone structure", and the other is that of a vortical fluid flow occurring at the tip of the dendrite. A relationship is also found which further indicates the importance of fluid flow. The cellular automata model developed in this dissertation has proven to be a valuable tool in gaining insight into the solidification process. The simulated growth is governed predominantly by the diffusion of solute and the Gibbs-Thomson effect. Solutal diffusion, is accurately treated, diffusing differently through liquid than through solid. The interface curvature is approximated using a template method, into which crystalline anisotropy has also been introduced. Several features were added to explore interface kinetics, solute partitioning, and fluid flow due to shrinkage. Simulations on a 100 x 100 system typically required less than a minute on a workstation, and only qualitative agreement with the experiments was sought. The partial differential equations for the evolution of a growing array of dendrites are derived taking into account only diffusion. It is explicitly shown how the non-conservative equations conserve all of the material in the solidifying system.
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Dhaubhadel, Rajan. "An experimental study of dense aerosol aggregations." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/663.
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Baggioli, Matteo. "Gravity, holography and applications to condensed matter." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/395205.
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Los sistemas fisicos fuertemente acoplados, junto a sus correspondientes y por lo general exoticas caracteristicas, son imposibles de tratar mediante los enfoques perturbativos convencionales que en estos casos no son capaces de proporcionar una herramienta controlable y robusta. Sin embargo, los efectos no perturbativos y fenomenos fuertemente correlacionados abundan en la fisica, especialmente en la Fisica de la Materia Condensada.
La correspondencia AdS / CFT, que nace de el estimulo de las ideas y esfuerzos empleados en descubrir una posible descripcion de la gravedad cuantica, proporciona una perspectiva inesperada e innovadora para hacer frente a las teorías de campo fuertemente acopladas. En su formulacion mas general este planteamiento ofrece un arma efectiva para hacer frente a ese tipo de problemas utilizando una descripcion dual de teorias gauge mediante teorias de gravedad que resulta ser mas simple que la original.
En los ultimos anos ha habido un gran numero de avances aplicando esta dualidad a temas modernos e innovadores en materia condensada, tales como la naturaleza de los metales raros o el mecanismo que subyace la superconductividad de alta Tc.
La relajacion del momento es un ingrediente omnipresente e inevitable de cualquier sistema realista en Materia Condensada. En los materiales del mundo real la presencia de un reticulo, de impurezas, o de desorden hacen que el momento se disipe, y se da lugar a efectos fisicos relevantes, tales como las propiedades de transporte de corriente continua sean finitas,es decir, la conductividad.
Hay varias preguntas abiertas relacionadas a dichas cantidades, especialmente en el limite de maxima relajacion donde surgen nuevos estados aislantes y transiciones de fase cuantica inesperadas entre los estados ultimos y metalicos (MIT) .
El objetivo principal de esta tesis es la introduccion de disipacion de momento y sus efectos en el contexto Ads/CMT, es decir, las aplicaciones de la dualidad Gauge-Gravedad en materia condensada.
Una manera conveniente y efectiva de romper la simetria traslacional de la teoria cuantica de campos dual es proporcionada por las teorias de gravedad masiva (GM), que constituye una herramienta facil y manejable para atacar varias e interesantes preguntas sobre sistemas fuertemente acoplados con disipacion de impulso. Originalmente concebido para resolver problemas en cosmologia, la GM puede ahora ser empleada bajo una perspectiva completamente nueva y podria convertirse en una herramienta útil para aplicaciones del ''mundo real'' y ''de bajas energias''. Consideramos modelos genericos de gravedad masiva en espacio-tiempos asintóticamente anti de Sitter y los analizamos usando tecnicas holograficas.Strongly coupled physical systems along with their corresponding, and usually exotic, features are elusive and not suitable to be described by conventional and perturbative approaches, which in those cases are not able to provide a controllable and robust tool for computations. Nevertheless non perturbative effects and strongly correlated frameworks are ubiquitous in nature, expecially in Condensed Matter physics. The AdS/CFT correspondence, born from the excitement of ideas and efforts employed in finding out a possible description of Quantum Gravity, lead to a flurry of fresh air into the subject, introducing an unexpected and brandnew perspective for dealing with strongly coupled field theories. In its more general formulation, known as Gauge-Gravity duality, this setup accounts for an effective and efficient weapon to tackle those kind of problems using a dual gravitational description which turns out to be way easier than the original one. In the last years, a huge number of developments have been achieved in applying the duality towards modern and hot condensed matter misteries, such as the Strange Metals nature or the mechanism underlying the High-Tc Superconductivity.\\ Momentum relaxation is an ever-present and unavoidable ingredient of any realistic Condensed Matter system. In real-world materials the presence of a lattice, impurities or disorder forces momentum to dissipate and leads to relevant physical effects such as the finiteness of the DC transport properties, i.e. conductivities. Several open questions are connected to those quantities expecially in the limit of strong momentum relaxation where novel insulating states appear and unexpected quantum phase transitions between the latter and metallic states (MIT) arise.\\[0.2cm] The main purpose of this thesis is the introduction of momentum dissipation and its consequent effects into the framework of AdS/CMT, namely the applications of the Gauge-Gravity duality to Condensed Matter. \\ A convenient and effective way of breaking translational symmetry of the the dual quantum field theory is provided by Massive Gravity (MG) theories, which constitues a tractable and easy tool to adress several interesting questions in strongly coupled systems with momentum dissipation. Born to solve cosmological puzzles, MG can now be reconsidered under a completely new perspective and could become a useful framework for ''Real-world" phenomena and "low energy" applications. We consider generic massive gravity models embedded into asymptotically Anti de Sitter spacetime and we analyze them using holographic techniques.
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Hamida, Youcef. "MAGNETISM IN A NUMBER OF METAL ORGANIC FRAMEWORKS (MOFs) WITH 1D AND 3D CHARACTERISTICS: AN EXPERIMENTAL AND ANALYTICAL STUDY." Diss., Temple University Libraries, 2012. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/195069.
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PhysicsPh.D.
Metal Organic Frameworks (MOFs) exhibit many excellent physical properties including magnetic properties for potential applications in devices. More importantly for the subject of this thesis, MOFs are ideal for the realization of low dimensional magnetism because of the large selection of ligands connecting magnetic centers in making the framework. The materials studied in this thesis include ten magnetic MOFs of the form M(L1)(L2) [M = Cu, Ni, Co, Fe, Mn; L1 = NDC, bpdc, BDC, BODC, N3; L2 = DMF, H2O, TED, bpy]. Polycrystalline powder samples as well as single crystal samples were synthesized. Their crystal structures were determined, and their magnetic and thermodynamic properties were measured and analyzed. Eight of these materials were characterized as 1D magnets and two as 3D magnets. In the 1D case it is found that above Tm [the temperature at which the magnetic susceptibility χ(T) has a peak] the magnetic behavior of MOFs (S ≥ 1) can be well described with the Classical Fisher Model (CFM). Near and below TC the spins take a more definite orientation than allowed for in the CFM and hence the Ising Model (IM) was used for fitting. Both CFM and IM yield fairly consistent intrachain couplings (J) when applied in their appropriate temperature region. To estimate the interchain exchange (J′), the susceptibility for a magnetic chain in the mean field of neighboring chains is used. In all cases, as expected, the ratio of J to J′ was less than 10%. The special case of Cu(N3)2bpy (S = ½) was analyzed with the spin ½ IM. Although the specific heat data (Ctotal) for most of the 1D MOFs showed no clear phase transition, a low temperature fit to the electron-phonon specific heats yielded apparent heavy fermion-like &gamma values on the order of several hundred mJ/mol K2. The lattice specific heat (C lattice) was estimated using a Debye-Einstein hybrid model. Subtracting Clattice from Ctotal, magnetic specific heat (CM) with a broad peak characteristic of low dimensional magnetism was obtained. The peak in CM was at temperature near that expected from χ(T) fits. The J values obtained from the magnetic specific heat fits were in good agreement with those obtained from χ(T) fits. Once the magnetic specific heat was accounted for, γtakes values in the expected range of few mJ/mol K2. For 3D MOFs [Mn(N3)2bpy and Fe(N3)2bpy], the existence of long range canted antiferromagnetic ordering was observed in both magnetic and specific heat measurements with phase transitions at 38 K and 20 K in the case of Mn(N3)2bpy and Fe(N3)2bpy, respectively. These transition temperatures are considered fairly high for molecular based materials. In both Mn(N3)2bpy and Fe(N3)2bpy, the χ(T) data fit well to the Heisenberg model for a diamond-type network. The transition can clearly be seen with an abrupt increase in the magnetization below TC and a shift to a higher temperature in the specific heat when measured under an applied magnetic field. The systematic approach in this work led to the successful estimate of C lattice resulting in meaningful fitting of χ(T) and Cmagnetic to the appropriate theoretical models in magnetism. It also led the discovery of ferrimagnets or canted antiferromagnets M(N3)2bpy with large coercivity and rather high transition temperature. The results of this study have been published in three articles in the Journal of Applied physics, and two manuscripts are under preparation for submission [1-5].
Temple University--Theses
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KIM, Eui-Jong. "Development of numerical models of vertical ground heat exchangers and experimental verification : domain decomposition and state model reduction approach." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00684138.
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Ground-source heat pump systems with vertical ground heat exchangers (GHE) are gaining popularity worldwide for their higher coefficients of performance and lower CO2 emissions. However, the higher initial cost of installing the borehole GHEs is a main obstacle to spread the systems. To reduce the required total GHE length and efficiently operate the systems, various systems such as hybrid ones (e.g. solar heat injection) have recently been introduced. Accurate prediction of heat transfer in and around boreholes of such systems is crucial to avoid costly overdesigns or catastrophic failures of undersized systems as it is for typical GCHP systems. However, unlike the traditional sizing methods, it is increasingly required to take into account detailed borehole configuration and transient effects (e.g. short circuit effects between U-tubes). Many of the existing GHE models have been reviewed. Some of these models have serious limitations when it comes to transient heat transfer, particularly in the borehole itself. Accordingly, the objective of this thesis is to develop a model that is capable to accurately predict thermal behaviors of the GHEs. A precise response to input variations even in a short time-step is also expected in the model. The model also has to account for a correct temperature and flux distribution between the U-tubes and inside the borehole that seems to be important in the solar heat injection case. Considering these effects in 3D with a detailed mesh used for describing the borehole configurations is normally time-consuming. This thesis attempts to alleviate the calculation time using state model reduction techniques that use fewer modes for a fast calculation but predict similar results. Domain decomposition is also envisaged to sub-structure the domain and vary the time-step sizes. Since the decomposed domains should be coupled one another spatially as well as temporally, new coupling methods are proposed and validated particularly in the FEM. For the simulation purpose, a hybrid model (HM) is developed that combines a numerical solution, the same one as the 3D-RM but only for the borehole, and well-known analytical ones for a fast calculation. An experimental facility used for validation of the model has been built and is described. A comparison with the experimental results shows that the relatively fast transients occurring in the borehole are well predicted not only for the outlet fluid temperature but also for the grout temperatures at different depths even in very short time-steps. Even though the current version of 3D-RM is experimentally validated, it is still worth optimizing the model in terms of the computational time. Further simulations with the 3D-RM are expected to be carried out to estimate the performance of new hybrid systems and propose its appropriate sizing with correspondent thermal impacts on the ground. Finally, the development of the model 3D-RM can be an initiation to accurately model various types of GHE within an acceptable calculation time.
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Hinton, Michael J. "Superfluidity in Ultrathin Cuprates and Niobium/Ferromagnetic Heterostructures." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1420673882.
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Andersson, Mikael Svante. "Interacting Magnetic Nanosystems : An Experimental Study Of Superspin Glasses." Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-319717.
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This thesis presents experimental results on strongly interacting γ-Fe2O3 magnetic nanoparticles and their collective properties. The main findings are that very dense randomly packed (≈60%) γ-Fe2O3 nanoparticles form a replica of a spin glass. The magnetic properties of the nanoparticle system are in most regards the same as those of an atomic spin glass. The system is therefore proposed as a model superspin glass. In superspin glasses the interacting building blocks that form the collective state are single domain nanoparticles, superspins with a magnetic moment of about 10000 μB, which can be compared to the atomic magnetic moment in spin glasses of approximately 1 μB. It was found that the relaxation time of the individual nanoparticles impacts the collective properties and governs the superspin dimensionality. Several dense compacts, each prepared with nanoparticles of a specific size, with diameters 6, 8, 9 and 11.5 nm, were studied. All the studied compacts were found to form a superspin glass state. Non-interacting reference samples, consisting of the same particles but coated with a silica shell, were synthesized to determine the single particle magnetic properties. It was also found that the effects of the nanoparticle size distribution, which lead to a variation of the magnetic properties, can be mitigated by having strong enough interparticle interactions. The majority of the work was carried out using SQUID magnetometry.
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Nawarange, Amruta V. "Optical Emission Spectroscopy during Sputter Deposition of CdTe Solar Cells and CuTe-Based Back Contacts." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1321656598.
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Stepanov, Petr. "Spin and Charge Transport in Monolayer and Trilayer Graphene in the Quantum Hall Regime." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1532103607994675.
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Triana, Carlos A. "Atomic short-range order, optical and electronic properties of amorphous transition metal oxides : An experimental and theoretical study of amorphous titanium aTiO2 and tungsten aWO3 solid thin-film oxides." Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-318193.
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Amorphous transition metal oxides [aTMOs], have emerged as innovative functional materials for wide-ranging electronic, optical and energy-related applications. However, no systematic and broadly applicable method exists to assess their atomic-scale correlations, and since the optical and electronic processes are local structure-dependent, still there are not well-stablished mechanisms that suitably explain the physical properties of aTMOs. This thesis presents experimental and theoretical studies of the atomic short-range order, optical and electronic properties, and state-defects induced by Li+-ion-intercalation and oxygen-vacancies in amorphous titanium aTiO2 and tungsten aWO3 thin-film oxides. Those properties play a key role for application in high energy-density Li+-ion batteries and in switchable dynamical modulation of solar-irradiation transmittance for energy efficient "smart windows", where the disorder-dependent Li+-ion-intercalation and oxygen-vacancy-induced defect-states influence charge-carrier transfer mechanisms. After introducing the scope of this thesis, the fundamental theoretical concepts describing the experimental findings on amorphous solids are reviewed. Thereafter, a comprehensive analysis on the optical absorption phenomena experimentally observed in oxygen-deficient and Li+-ion-intercalated aLixTiO2−y and aLixWO3−y thin-films and a discussion on the electrochromic properties are presented. The optical absorption is described in the framework of the small polaron absorption model. Finally, a state-of-the-art systematic procedure involving theory and experiment in a self-consistent computational framework is implemented to unveil the atomic-scale structure of aTiO2 and aWO3, and its role for the electronic properties. The procedure is based in Reverse Monte Carlo [RMC] and Finite Difference Method [FDM] simulations of X-ray-Absorption spectra to construct a disordered theoretical model having the same bonding and coordination distribution as the experimental system. Ab-initio molecular dynamics simulations and density functional theory are then used to assess defect-states induced by Li+-ion-intercalation and oxygen-vacancies in aTiO2 and aWO3 oxides. The schemes introduced in this study offer a consistent route to experimentally and theoretically assess the role of the atomic-scale structure on the optical and electronic properties of aTiO2 and aWO3 and could be extended to the study of other aTMOs. The final results provide crucial insight towards the understanding of optical and electronic mechanisms where disorder-dependent ion-intercalation and oxygen-vacancy-induced localized defect-states influence charge transfer mechanisms of crucial importance for wide ranging optical and energy-related application of aTiO2 and aWO3 oxides.
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Wolfe, Christopher Stuart. "Novel Techniques for Detection and Imaging of Spin Related Phenomena: Towards Sub-Diffraction Limited Resolution." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437316315.
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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.
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Mroz, Michael V. "Characterization of Morphological and Chemical Properties of Scandium Containing Cathode Materials." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou158470102410177.
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Paul, Sanjoy. "CHARGE TRANSPORT IN LIQUID CRYSTALLINE SMECTIC AND DISCOTIC ORGANIC SEMICONDUCTORS: NEW RESULTS AND EXPERIMENTAL METHODOLOGIES." Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1469836810.
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Saers, Robert. "Ultracold rubidium atoms in periodic potentials." Doctoral thesis, Umeå universitet, Fysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1821.
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This thesis includes both experimental and theoretical investigations, presented in a series of eight papers. The experimental part ranges from the construction procedures of an apparatus for Bose-Einstein condensates, to full scale experiments using three different set-ups for ultracold atoms in optical lattices. As one of the main themes of the thesis, an experimental apparatus for production of Bose-Einstein Condensates is under construction. A magneto-optically trapped sample, hosting more than 200 million 87Rb atoms, have successfully been loaded into a magnetic trap with high transfer rate. The lifetime of the sample in the magnetic trap is in the range of 9 s, and the atoms have been shown to respond to evaporative cooling. The experiment is ready for optimization of the magnetic trap loading, and evaporative cooling parameters, which are the final steps for reaching Bose-Einstein condensation. The set-up is designed to host experiments including variable geometry optical lattices, and includes the possibility to align laser beams with high angular precision for this purpose. The breakdown of Bloch waves in a Bose-Einstein condensate is studied, attributed to the effect of energetic and dynamical instability. This experimental study is performed using a Bose-Einstein condensate in a moving one-dimensional optical lattice at LENS, Florence Italy. The optical lattice parameters, and the thermal distribution of the atomic sample required to trigger the instabilities, are detected, and compared with a theoretical model developed in parallel with the experiments. In close connection with these one-dimensional lattice studies, an experimental survey to characterize regimes of superradiant Rayleigh scattering and Bragg scattering is presented. Tunneling properties of repulsively bound atom pairs in double well potentials are characterized in an experiment at Johannes Gutenberg University, Mainz Germany. A three-dimensional optical lattice, producing an array of double wells with tunable properties is let to interact with a Bose-Einstein condensate. Pairs of ultracold atoms are produced on one side in the double wells, and their tunneling behavior, dependent on potential barrier and repulsion properties, is studied. A theoretical study of the crossover between one- and two-dimensional systems has been performed. The simulations were made for a two-dimensional array of atoms, where the behavior for different tunneling probabilities and atom-atom repulsion strengths was studied. Scaling relations for systems of variable sizes have been examined in detail, and numerical values for the involved variables have been found.
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Xu, Jinsong. "Electronic and Spin Dependent Phenomena in Two-Dimensional Materials and Heterostructures." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531925662989238.
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Michel, Amelie. "Etude du comportement des gaz de fission dans le dioxyde d'uranium : mécanismes de diffusion, nucléation et grossissement de bulles." Phd thesis, Université de Caen, 2011. http://tel.archives-ouvertes.fr/tel-00691286.
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Lors de l'irradiation en réacteur du combustible, sont générés des gaz de fission, principalement xénon et krypton, soumis à plusieurs phénomènes : la diffusion et la précipitation. Ces différents phénomènes peuvent avoir des conséquences néfastes sur les propriétés physico-chimiques du combustible et sur son comportement en réacteur. L'objectif de ce travail est d'améliorer la compréhension du comportement des gaz de fission en identifiant les mécanismes régissant les phénomènes de diffusion, de nucléation et de grossissement de bulles. Pour ce faire, des études à effets séparés ont été mises en place couplant des irradiations/implantations aux ions à des caractérisations fines sur Grands Instruments. L'influence de plusieurs paramètres tels que le type de gaz, sa concentration et la température a été mise en évidence. L'interprétation des mesures de relâchement réalisées par Spectrométrie de Désorption Thermique au CENBG de Bordeaux, a permis de déterminer des coefficients de diffusion du xénon et du krypton dans le dioxyde d'uranium. Un mécanisme de nucléation hétérogène sur les germes de défauts a été démontré à l'aide d'expériences sur la plate-forme JANNuS d'Orsay couplant un implanteur, un accélérateur et un Microscope Electronique en Transmission (MET). Enfin, des caractérisations par MET et par spectroscopie d'absorption X d'échantillons implantés en gaz et recuits ont mis en évidence le grossissement des bulles par capture d'atomes de gaz et de lacunes.
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Tayade, Renuka. "Theoretical and experimental contribution to the study of exchange-spring magnets." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2014. http://tel.archives-ouvertes.fr/tel-01062741.
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This thesis is divided into two parts, experimental part presenting the synthesis of exchange spring magnets and theoretical part showing the magnetization dynamics of exchange spring magnets. For the synthesis, ferrite and metal alloy based magnets using mechanical milling and ultrasonic mixing are studied. This part discusses the difficulty in controlling the microstructure during synthesis. Several samples with varying volume fractions of the soft phase are synthesized. It is found that mechanical milling initiates a reaction and this leads to disintegration of the ferrite phase into its intermediate phases. Samples prepared using ultrasonic mixing however show presence of the ferrite phase up to very large volume fraction of the soft alloy phase which provides better perspective for the synthesis. Dynamics of the exchange spring system is studied theoretically using micromagnetic theory. Microwave assisted magnetization reversal are studied in the bulk bilayer exchange coupled system. We investigate the nonlinear magnetization reversal dynamics in a perpendicular exchange spring media using the Landau-Lifshitz equation. In the limit of the infinite thickness of the system, the propagation field leads the reversal of the system. The reduction of the switching field and the magnetization profile in the extended system are studied numerically. The possibility to study the dynamics analytically is discussed and an approximation where two P-modes are coupled by an interaction field is presented. The ansatz used for the interaction field is validated by comparison with the numerical results. This approach is shown to be equivalent to two exchange coupled macrospins.
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Borshch, Volodymyr. "Nanosecond Electric Modification of Order Parameters." Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1416443341.
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Pesquera, Herrero David. "Strain and interface-induced charge, orbital and spin orderings in transition-me tal oxide perovskites." Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/283932.
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Courtois, Hervé. "Supraconductivité de proximité dans les nanostructures métalliques artificielles." Phd thesis, Université Joseph Fourier (Grenoble), 1994. http://tel.archives-ouvertes.fr/tel-00116792.
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Nous avons étudié l'effet de proximité dans un système mésoscopique comportant un conducteur de métal normal N en contact avec des îles supraconductrices S latérales. Une méthode d'évaporation métallique oblique sur un masque submicronique suspendu a été mise au point sous ultra-vide, nous permettant de contrôler la qualité de l'interface N-S depuis un contact métallique parfait jusqu'à une barrière tunnel. Nous présentons un nouveau type de filtre haute-fréquence large bande, minituarisé sur un substrat de cuivre, efficace jusqu'à très haute fréquence (20 GHz) et dédié au filtrage absolu d'échantillons mésoscopiques. Les mesures de transport jusqu'à très basse température (20 mK) montrent que le comportement du transport dans un métal normal en proximité avec un supraconducteur dépend fortement des paramètres microscopiques que sont la longueur de cohérence des paires d'électrons, la longueur équivalente de barrière à l'interface et la dimension latérale des jonctions. Le couplage Josephson montre un comportement en température nouveau, décrit par les modèles classiques dans un régime propre pour la longueur de cohérence normale. L'observation de centres de gliseement de phase à basse température exemplifie le caractère de bande interdite nulle de la supraconductivité de proximité. Dans une géométrie de réseau bideimensionnel, un nouveau régime d'anisotropie extrême est réalisé, se caractérisant par une oscillation très piquée de la température de transition résistive en fonction du champ magnétique. Dans un conducteur normal en anneau, un flux magnétique permet de piloter l'interférence entre les courants supraconducteurs selon un effet de type SQUID. Les corrections de conductance liées à la localisation faible dans le conducteur normal au voisinage d'une interface N-S sont également discutées. Nous présentons enfin une expérience décisive afin de tester l'effet du blocage de Coulomb sur l'effet de proximité dans une jonction N-S en régime tunnel.
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Chevalier, Alexis. "ETUDE EXPERIMENTALE, ELABORATION ET MODELISATION DE MATERIAUX COMPOSITES A BASE DE POUDRES MAGNETIQUES DOUCES." Phd thesis, Université de Bretagne occidentale - Brest, 1998. http://tel.archives-ouvertes.fr/tel-00484041.
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Les procédés de dépôts en couche épaisses, que l'on retrouve dans la mise en oeuvre des systèmes de communications et de détections, sont à l'origine de l'intérêt croissant pour les matériaux magnétiques composites. Ces matériaux sont obtenus par mélange, en proportions variables, d'une ou plusieurs poudres magnétiques choisies en fonction de leurs propriétés originales et de poudres non magnétiques. Ce travail est une étude fondamentale des propriétés magnétiques des matériaux composites, et a pour but la modélisation de leur susceptibilité magnétique en champ faible. Le modèle que nous proposons pour décrire les propriétés magnétiques de ces matériaux composites est issu, comme la majorité des lois de mélanges, d'une théorie de champ moyen. L'intérêt de ce modèle est de présenter une forme analytique compacte qui ne fait intervenir qu'un nombre restreint de paramètres dont le sens physique a été défini dans cette étude. Le premier paramètre est la susceptibilité intrinsèque Xi, liée aux propriétés magnétiques des constituants du mélange. L'étude expérimentale, menée sur des composites à base de poudre de ferrites, a permis de montrer que l'aimantation de ces matériaux composites se fait principalement par rotation des moments ce qui nous a conduit à identifier Xi à la susceptibilité rotationnelle de la poudre magnétique utilisée. Le second paramètre intervenant dans notre modèle est le coefficient effectif de forme N, lié au caractère dispersé de la matière. Il tient compte de manière globale de l'ensemble des interactions qui dépendent à la fois de la forme des particules et de leurs arrangements sous forme d'agrégats. L'aptitude du modèle à prédire les comportements de la susceptibilité magnétique des matériaux composites a été vérifiée de façon expérimentale du domaine statique jusqu'aux hyperfréquences.
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BARBERET, Philippe. "Développement d'une ligne d'irradiation microfaisceau en mode ion par ion pour la radiobiologie expérimentale à l'échelle cellulaire." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2003. http://tel.archives-ouvertes.fr/tel-00004084.
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Un dispositif micro-irradiation par ions isolés a été développé au CENBG pour des applications en radiobiologie à l'échelle cellulaire. Cette installation consiste en un aménagement de la ligne microfaisceau préexistante qui permet déjà d'obtenir un faisceau de protons ou de particules alpha entre 1 et 3 MeV, de faible intensité, et d'une résolution spatiale sous vide inférieure au micromètre. La majeure partie de ce travail a consisté à développer un étage d'irradiation adaptable sur la microsonde et permettant de délivrer les ions à l'air avec une précision absolue de quelques micromètres. Un programme permettant le contrôle de la totalité des instruments ainsi que des phases d'étalonnage et d'irradiation automatiques a également été mis au point. Des outils de simulation Monte Carlo, nécessaires à la caractérisation et à l'optimisation du dispositif et notamment en terme de résolution spatiale, ont été validés à l'échelle du micromètre par comparaison à des résultats expérimentaux. Les performances du dispositif, notamment en terme de contrôle du nombre d'ions, de résolution spatiale et de précision d'irradiation ont été testées sous faisceau. Les résultats obtenus permettent d'envisager les premières applications dans des études de radiobiologie. Dans un futur proche cet outil va permettre l'étude des réponses cellulaires aux faibles doses, allant jusqu'au cas extrême d'un ion pour une cellule. Il devrait permettre par ailleurs d'aborder des mécanismes cellulaires fondamentaux tels la signalisation, la communication intercellulaire ou encore la mort cellulaire programmée (apoptose).
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Bhallamudi, Vidya Praveen. "Spins in heterogeneous landscapes: Consequences for transport and imaging." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1306871981.
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Skorobogatiy, Maksim 1974. "Numerical methods in condensed matter physics." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/82756.
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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (leaves 62-63).
by Maksim A. Skorobogatiy.
M.Eng.
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Wang, Ruizhe. "Magnetic fluctuations and clusters in the itinerant ferromagnet Ni-V close to a disordered quantum critical point." Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent1555936445433091.
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Clifford, Dustin M. "Non-Conventional Approaches to Syntheses of Ferromagnetic Nanomaterials." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4205.
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The work of this dissertation is centered on two non-conventional synthetic approaches to ferromagnetic nanomaterials: high-throughput experimentation (HTE) (polyol process) and continuous flow (CF) synthesis (aqueous reduction and the polyol process). HTE was performed to investigate phase control between FexCo1-x and Co3-xFexOy. Exploration of synthesis limitations based on magnetic properties was achieved by reproducing Ms=210 emu/g. Morphological control of FexCo1-x alloy was achieved by formation of linear chains using an Hext. The final study of the FexCo1-x chains used DoE to determine factors to control FexCo1-x, diameter, crystallite size and morphology. [Ag] with [Metal] provide statistically significant control of crystallite size. [OH]/[Metal] predict 100 % FexCo1-x at > 30. To conclude section 1, a morphological study was performed on synthesis of Co3-xFexOy using the polyol process. Co3-xFexOy micropillars were synthesized at various sizes. The close proximity of the particles in the nanostructure produced an optical anisotropy and was magnetically induced which is evidence for the magneto-birefringence effect.
The second non-conventional synthetic approach involves continuous flow (CF) chemistry. Co nanoparticles (Ms=125 emu/g) were newly synthesized by aqueous reduction in a microreactor and had 30 ±10 nm diameter and were produced at >1g/hr, a marker of industrial-scale up viability. The final work was the CF synthesis of FexCo1-x. The FexCo1-x was synthesized with limitation to the composition. The maximum FexCo1-x phase composition at 20 % resulted from the aqueous carrier solvent triggering oxide formation over FexCo1-x.
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Zhao, Hongming. "ETUDE EXPERIMENTALE DE LA PROPRIETE DE COUPLAGE SPIN-ORBITE DANS DES STRUCTURES SEMI-CONDUCTRICES DE BASSE DIMENSIONALITE." Phd thesis, Université de Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00595906.
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Nous avons étudié les propriétés optiques et le couplage spin-orbite dans différentes structures semi-conductrices de basse dimension. Tout d'abord, la dynamique de spin dans des gaz d'électrons bidimensionnels d'une hétérostructure GaAs/AlGaAs (001) a été étudiée par la technique de rotation Kerr résolue en temps. Les résultats montrent que la durée de vie du spin dans le plan du puits est anisotrope et que la densité des électrons affecte fortement le couplage spin-orbite de type Rashba. Nous avons observé ensuite une grande anisotropie du facteur g de l'électron dans des puits quantiques GaAs/AlGaAs (001) asymétriques, et la dépendance en température de son amplitude a été mesurée. Deuxièmement, nous avons fait l'étude expérimentale du dédoublement du spin électronique dans le plan des puits GaN/AlGaN C(0001) à température ambiante. La mesure du courant de l'effet photo-galvanique circulaire montre clairement un dédoublement isotrope dans le plan du puits. Troisièmement, les premières mesures du facteur g dans des films minces de GaAsN à température ambiante a été faite par la technique de rotation Kerr résolue en temps. Elles montrent que le facteur g peut être modifié drastiquement par l'introduction d'une petite quantité d'azote dans GaAs. Enfin, les caractéristiques optiques de transitions indirectes dans des séries de nano-bâtonnets linéaire CdTe/CdSe/CdTe de taille et de forme variables ont été étudiées par photoluminescence stationnaire et résolue en temps. Nos résultats montrent le transfert progressif d'une transition optique directe (type I) au sein de CdSe vers une transition indirecte (type II) entre CdSe/CdTe à mesure que la longueur des nano-bâtonnets augmente.
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Moussavi-Madani, Mahmoud. "Positron interactions in condensed matter." Thesis, Royal Holloway, University of London, 1987. http://repository.royalholloway.ac.uk/items/78c4cb98-6511-4083-8827-9172a34368aa/1/.
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Positron annihilation has been studied in a number of solids, and at some condensed monolayer surfaces. The bulk specimens, which included cadmium, tin, selenium, and graphite, yielded information on lattice defects and phase transitions. Two dimensional layers of condensed gases, including argon, nitrogen, oxygen and helium result in positronium formation suggesting the existence of positron surface traps. The Doppler broadening method has been applied to these studies. The 511-Kev Gamma-rays resulting from the annihilation of positrons with electrons was detected by a Germanium detector with high resolution. The cadmium and tin specimens were plastically deformed at 77K and measurements with increasing temperature provided information on phase transitions, annealing processes and on the nature of the defects concerned. The application of the positron trapping model provides values of the vacancy formation energy (enthalpy) and of the concentration of monovacancies and divacancies. The energy spectra were analysed, with Gaussian and Parabolic components convoluted with instrumental resolution function, to indicate the proportion of annihilation of positrons with core and conduction electrons. An important result of the work on tin was the observation of the phase transition of white-tin to gray-tin at 240K. Positron trapping at graphite surfaces, and the formation of positronium has been observed by introducing a parameter R, related to the positronium fraction in this work. The growth of monolayers of gases condensed on graphite has been observed in the changing of the total area of the annihilation line shape spectrum, and also in the changing positronium fraction parameter. Estimated values of adsorption energies are discussed.
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Morris, Andrew James. "A stochastic approach to condensed matter physics." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608498.
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Gentle, Simon Adam. "Holography, black holes and condensed matter physics." Thesis, Durham University, 2013. http://etheses.dur.ac.uk/7286/.
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In this thesis we employ holographic techniques to explore strongly-coupled quantum field theories at non-zero temperature and density. First we consider a state dual to a charged black hole with planar horizon and compute retarded Green's functions for conserved currents in the shear channel. We demonstrate the intricate motion of their poles and stress the importance of the residues at the poles beyond the hydrodynamic regime. We then explore the collective excitations of holographic quantum liquids arising on D3/D5 and D3/D7 brane intersections as a function of temperature and magnetic field in the probe limit. We observe a crossover from hydrodynamic charge diffusion to a sound mode similar to the zero sound mode in the collisionless regime of a Landau Fermi liquid. The location of this crossover is approximately independent of the magnetic field. The sound mode has a gap proportional to the magnetic field, leading to strong suppression of spectral weight for intermediate frequencies and sufficiently large magnetic fields. In the second part we explore the solution space of AdS gravity in the hope of learning general lessons about such theories. First we study charged scalar solitons in global AdS4. These solutions have a rich phase space and exhibit critical behaviour as a function of the scalar charge and scalar boundary conditions. We demonstrate how the planar limit of global solitons coincides generically with the zero-temperature limit of black branes with charged scalar hair. We exhibit these features in both phenomenological models and consistent truncations of eleven-dimensional supergravity. We then discover new branches of hairy black brane in SO(6) gauged supergravity. Despite the imbalance provided by three chemical potentials conjugate to the three R-charges, there is always at least one branch with charged scalar hair, emerging at a temperature where the normal phase is locally thermodynamically stable.
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Yang, Xu. "Symmetry and topology in condensed matter physics:." Thesis, Boston College, 2021. http://hdl.handle.net/2345/bc-ir:109160.
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Thesis advisor: Ying RanRecently there has been a surging interest in the topological phases of matter, including the symmetry-protected topological phases, symmetry-enriched topological phases, and topological semimetals. This thesis is aiming at finding new ways of searching and probing these topological phases of matter in order to deepen our understanding of them. The body of the thesis consists of three parts. In the first part, we study the search of filling-enforced topological phases of matter in materials. It shows the existence of symmetry-protected topological phases enforced by special electron fillings or fractional spin per unit-cell. This is an extension of the famous Lieb-Schultz-Mattis theorem. The original LSM theorem states that the symmetric gapped ground state of the system must exhibit topological order when there's fractional spin or fractional electron filling per unit-cell. However, the LSM theorem can be circumvented when commensurate magnetic flux is present in the system, which enlarge the unit-cells to accommodate integer numbers of electrons. We utilize this point to prove that the ground state of the system must be a symmetry-protected topological phase when magnetic translation symmetry is satisfied, which we coin the name “generalized LSM theorem”. The theorem is proved using two different methods. The first proof is to use the tensor network representation of the ground state wave-function. The second proof consists of a physical argument based on the idea of entanglement pumping. As a byproduct of this theorem, a large class of decorated quantum dimer models are introduced, which satisfy the condition of the generalized LSM theorem and exhibit SPT phases as their ground states. In part II, we switch to the nonlinear response study of Weyl semimetals. Weyl semimetals (WSM) have been discovered in time-reversal symmetric materials, featuring monopoles of Berry’s curvature in momentum space. WSM have been distinguished between Type-I and II where the velocity tilting of the cone in the later ensures a finite area Fermi surface.To date it has not been clear whether the two types results in any qualitatively new phenomena. In this part we focus on the shift-current response ($\sigma_{shift}(\omega)$), a second order optical effect generating photocurrents. We find that up to an order unity constant, $\sigma_{shift}(\omega)\sim \frac{e^3}{h^2}\frac{1}{\omega}$ in Type-II WSM, diverging in the low frequency $\omega\rightarrow 0$ limit. This is in stark contrast to the vanishing behavior ($\sigma_{shift}(\omega)\propto \omega$) in Type-I WSM. In addition, in both Type-I and Type-II WSM, a nonzero chemical potential $\mu$ relative to nodes leads to a large peak of shift-current response with a width $\sim |\mu|/\hbar$ and a height $\sim \frac{e^3}{h}\frac{1}{|\mu|}$, the latter diverging in the low doping limit. We show that the origin of these divergences is the singular Berry’s connections and the Pauli-blocking mechanism. Similar results hold for the real part of the second harmonic generation, a closely related nonlinear optical response. In part III, we propose a new kind of thermo-optical experiment: the nonreciprocal directional dichroism induced by a temperature gradient. The nonreciprocal directional dichroism effect, which measures the difference in the optical absorption coefficient between counterpropagating lights, occurs only in systems lacking inversion symmetry. The introduction of temperature-gradient in an inversion-symmetric system will also yield nonreciprocal directional dichroism effect. This effect is then applied to quantum magnetism, where conventional experimental techniques have difficulty detecting magnetic mobile excitations such as magnons or spinons exclusively due to the interference of phonons and local magnetic impurities. A model calculation is presented to further demonstrate this phenomenon
Thesis (PhD) — Boston College, 2021
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Zonzo, Giuseppe. "Quantum Information Theory in Condensed Matter Physics." Doctoral thesis, Universita degli studi di Salerno, 2017. http://hdl.handle.net/10556/2625.
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2015 - 2016Inthe“standard”Gizburg-Landauapproach,aphasetransitionisintimately connected to a local order parameter, that spontaneously breaks some symmetries. In addition to the “traditional” symmetry-breaking ordered phases, a complex quantum system exhibits exotic phases, without classical counterpart, that can be described, for example, by introducing non-local order parameters that preserve symmetries. In this scenario, this thesis aims to shed light on open problems, such as the localdistinguishabilitybetweengroundstatesofasymmetry-breakingordered phase and the classification of one dimensional quantum orders, in terms of entanglement measures, in systems for which the Gizburg-Landau approach fails. In particular, I briefly introduce the basic tools that allow to understand the nature of entangled states and to quantify non-classical correlations. Therefore, I analyze the conjecture for which the maximally symmetry-breaking ground states (MSBGSs) are the most classical ones, and thus the only ones selected in real-world situations, among all the ground states of a symmetry-breaking ordered phase. I make the conjecture quantitatively precise, by proving that the MSBGSs are the only ones that: i) minimize pairwise quantum correlations, as measured by the quantum discord; ii) are always local convertible, by only applying LOCC transformations; iii) minimize the residual tangle, satisfying at its minimum the monogamy of entanglement. Moreover,Ianalyzehowevolvesthedistinguishability,afterasuddenchange of the Hamiltonian parameters. I introduce a quantitative measure of distinguishability, in terms of the trace distance between two reduced density matrices. Therefore, in the framework of two integrable models that falls in two different classes of symmetries, i.e. XY models in a transverse magnetic field and the N-cluster Ising models, I prove that the maximum of the distinguishability shows a time-exponential decay. Hence, in the limit of diverging time, all the informations about the particular initial ground state disappear, even if a system is integrable. Far away from the Gizburg-Landau scenario, I analyze a family of fullyanalyticalsolvableonedimensionalspin-1/2models,namedtheN-clustermodels in a transverse magnetic field. Regardless of the cluster size N + 2, these modelsexhibitaquantumphasetransition,thatseparatesaparamagneticphase from a cluster one. The cluster phase coresponds to a nematic ordered phase or a symmetry-protected topological ordered one, for even or odd N respectively. Using the Jordan-Wigner transformations, it is possible to diagonalize these models and derive all their spin correlation functions, with which reconstruct their entanglement properties. In particular, I prove that these models have only a non-vanishing bipartite entanglement, as measured by the concurrence, between spins at the endpoints of the cluster, for a magnetic field strong enough. Moreover, I introduce the minimal set of nonlinear ground-states functionals to detect all 1-D quantum orders for systems of spin-1/2 and fermions. I show that the von Neumann entanglement entropy distinguishes a critical systemfromanoncriticalone,becauseofthelogarithmicdivergenceataquantum critical point. The Schmidt gap detect the disorder of a system , because it saturates to a constant value in a paramagnetic phase and goes to zero otherwise. The mutual information, between two subsystems macroscopically separated, identifiesthesymmetry-breakingorderedphases,becauseofitsdependenceon the order parameters. The topological order phases, instead, via their deeply non-locality, can be characterized by analyzing all three functionals. [edited by author]
In aggiunta alle tradizionali fasi ordinate con rottura spontanea di simmetria, ben descritte con un approccio alla Gizburg-Landau, dove una transizione di fase `e intimamente connessa alla rottura spontanea di qualche simmetria e ad un parametro d’ordine locale, un sistema quantistico presenta anche fasi esotiche,senzaanalogoclassico,chesonoperesempiocaratterizzatedaparametri d’ordine non locali, senza una necessaria rottura di simmetria. Partendo da questi presupposti, questa tesi si pone come obiettivo quello di fare luce su alcuni problemi ancora aperti, come la distinguibilit`a tra stati fondamentaliinsistemiquantisticiconrotturaspontaneadisimmetriaelaclassificazionedituttelefasipresentiinsistemiunidimensionalidispin-1/2efermioni, per i quali l’approccio alla Gizburg-Landau non fornisce una descrizione adeguata. Inparticolare,sid`aunaspiegazioneall’ipotesisecondolaqualeglistatifondamentali che rompono massimamente la simmetria sono quelli pi`u classici, e quindi selezionati dalla decoerenza dell’ambiente, tra tutti gli stati fondamentali,edenergeticamenteequivalenti,diunafaseordinataconrotturaspontanea di simmetria. Si dimostra, infatti, che gli stati che rompono massimamente la simmetria sono gli unici stati che soddisfano tre criteri di classicalit`a: i) minimizzano l’entanglement bipartito, come quantificato dalla discord; ii) sono gli uniciversocuituttiglialtristatifondamentalisonolocalmenteconvertibili,mediante LOCC; iii) minimizzano il tangle residuo, soddisfacendo al minimo la monogamia dell’entanglement. Viene analizzato, inoltre, come evolve la distinguibilit`a tra stati fondamentali, dopo un quench dei parametri Hamiltoniani. Dopo aver introdotto una misura quantitativa della distinguibilit`a, in termini della distanza tra due matrici densit`a ridotte, si dimostra, per due sistemi integrabili con diverse classi di simmetria, nel dettaglio il modello XY in campo magnetico e i modelli NclusterIsing,cheladistinguibilit`adecadeesponenzialmenteneltempoequindi, nel limite di tempi lunghi, tutte le informazioni sullo stato fondamentale di partenza si perdono, anche per sistemi integrabili, nei quali la termalizzazione non si verifica. LontanodalloscenarioGizburg-Landau,sianalizzaunafamigliadimodelli di spin-1/2 esattamente risolvibili, nel dettaglio i modelli N-cluster in campo magnetico, che mostrano una transizione tra una fase disordinata e una di tipo cluster, che pu`o essere nematica o topologica, rispettivamente per N pari o dispari. Usando le trasformazioni di Jordan-Wigner `e possibile diagonalizzare questi modelli, ricavare lo stato fondamentale, le funzioni di correlazione fermioniche e tutte le loro propriet`a di entanglement di. Si dimostra che questi modellinonhannoentanglementmultipartito,masoloentanglementbipartito, come misurato dalla concurrence, tra due spin alle estremit`a del cluster, per un campo magnetico sufficientemente intenso. Inoltre, sidimostrachel’entropiadivonNeumann,loSchmidtgapelamutualinformationrappresentanoilsetminimodifunzionalinonlinearidellamatrice densit`a ridotta, mediante le quali caratterizzare tutte le fasi presenti in sistemi unidimensionali di spin -1/2 e fermioni. In particolare, l’entropia di von Neumann caratterizza la criticalit`a del sistema, per la sua divergenza logaritmica al punto critico; lo Schmidt gap caratterizza il disordine di un sistema, perch´e satura ad un valore costante nelle fasi disordinate e va rapidamente a zero altrove; la mutual information cattura le fasi ordinate con rottura spontanea di simmetria, per le quali cio` e `e possibile definire un parametro d’ordine diverso da zero su un supporto finito. Le fasi topologiche, per via della loro natura fortemente non locale, necessitano di tutte e tre i funzionali per essere individuate. [a cura dell'autore]
XV n.s.
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Barranco, López Alejandro. "Applications of Supersymmetry: Exact Results, Gauge/Gravity Duality and Condensed Matter." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/284195.
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The study of supersymmetry has led us to a better understanding of field theories, specially in the strong coupling regime. In this thesis we have tried to show this through several examples. These are:
- The first of these examples has been the application of localization techniques in supersymmetric theories. Specifically, we have used the partition function of N=2 supersymmetric Chern-Simons theory with gauge group U(N) and 2Nf flavors. To regularize the theory, it is necessary to make the computation in a three sphere whose radius, R, serves as an IR regulator which can be taken to infinity at the end of the computation.
Once we have the exact partition function in terms of a matrix integral, we can solve the integral by means of a saddle-point approximation. This approximation becomes exact in the large N limit. The saddle-point equation can be solved exactly and in the decompactification limit it shows different phases depending on the value of the 't Hooft coupling.
We have also computed the free energy and the vacuum expectation value of a Wilson loop for a big circle of the three sphere. Both of them show discontinuities in their derivatives, in particular, the discontinuity in the free energy appears in the third derivative and thus, both phase transitions are third order.
- Other application that we have seen consists of the use of the gauge/gravity duality. In particular, starting from the gravity dual to N=1 super Yang-Mills, proposed by Maldacena and Núñez, we have reviewed how to add flavors (quarks) to this theory, without mass first and with mass later. We have also seen how to extract information about the field theory from these gravity duals, we have paid special attention to how the beta-function of the field theory dual is obtained from the gravity background proposed by Conde, Gaillard and Ramallo, dual to N=1 super Yang-Mills field theory with Nf massive flavors and a quartic superpotential.
The main result from the point of view of the field theory is that, in the case Nf=2N, the beta-function shows a non-trivial UV fixed point, which hints on possible IR fixed point as proposed by Seiberg in the conformal window picture. No evidence of non-trivial fixed points is found for Nf different from 2N.
- Again, in the context of the gauge/gravity duality, we have studied how to generate new supergravity solutions applying T-duality and how this affects the G-structures that describe the supersymmetry of these solutions. We have applied T-duality to the IIB supergravity solution of Klebanov and Witten with flavors. The supersymmetry of these backgrounds can be described by an SU(3)-structure and an SU(2)-structure before and after T-dualizing, respectively.
- Finally, we have presented an N=1 supersymmetric model that exhibits a superconducting phase transition. This model is based on a quartic Kähler potential for a chiral multiplet and no superpotential. The main difference with standard superconductivity is that the phase transition becomes first order rather than second order. Another difference is that, as it is typical in supersymmetric theories, the dependence on the cut-off is softened in our model.El estudio de supersimetría nos ha permitido un mejor entendimiento de las teorías de campos, especialmente en el régimen de acoplamiento fuerte. En esta tesis hemos tratado de mostrar esto a través de varios ejemplos. A saber: - Primero hemos mostrado cómo calcular de manera exacta con técnicas de localización la función de partición de la teoría de Chern-Simons supersimétrica N=2 con grupo gauge U(N) y 2Nf sabores en una tres esfera. Una vez que tenemos la función de partición exacta en términos de una integral de matrices, podemos resolverla por medio de la aproximación de punto silla. Esta aproximación se vuelve exacta cuando tomamos el límite de N grande. En el límite de descompactificación calculamos la energía libre y el valor de expectación de un lazo de Wilson correspondiente a un círculo máximo de la tres-esfera, mostrando transiciones de fase de tercer orden. - Otra aplicación ha consistido en el uso de la dualidad gravedad/gauge. Hemos revisado como construir una solución de supergravedad dual a la teoría N=1 super Yang-Mills con Nf sabores masivos y un superpotencial cuártico. El principal resultado desde el punto de vista de la teoría de campos que corresponde a dicha solución, consiste en que, en el caso Nf=2N, la función beta exhibe un punto fijo UV no trivial que da lugar a indicios acerca de un punto fijo IR adicional tal y como propone Seiberg en su propuesta de la ventana conforme. - También en el contexto de la dualidad gravedad/gauge hemos estudiado cómo generar nuevas soluciones de supergravedad por medio de la aplicación de T-dualidad a la solución de supergravedad de Klebanov y Witten con sabores. La supersimetría de estas soluciones pueden ser descritas en términos de una SU(3) estructura antes de T-dualizar, o una SU(2)-estructura, después de T-dualizar. - Finalmente, hemos presentado un modelo supersimétrico que exhibe una transición de fase superconductora basado en un potencial de Kähler cuártico para un multiplete quiral y sin superpotencial. Encontramos dos diferencias con superconductores usuales: nuestro modelo exhibe una transición de fase de primer orden, en lugar de ser de segundo orden, y la dependencia con la energía de corte es más suave.
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Liyanage, Geethika Kaushalya. "Infrared Emitting PbS Nanocrystals through Matrix Encapsulation." Bowling Green State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1403953924.
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Runge, Katharina. "Visualisation de fluxoides dans des réseaux 2D artificiels supraconducteurs." Phd thesis, Grenoble 1, 1993. http://tel.archives-ouvertes.fr/tel-00356016.
Full textAbstract:
Nous avons mis au point une cellule de décoration, permettant de décorer les vortex à basse température (jusqu'à 1.6K) sous faible champ magnétique (jusqu'à 0.2mT). La méthode est basée sur l'interaction des gradients de champs dus aux vortex avec des particules ferromagnétiques fabriquées in-situ dans un gaz résiduel. Après réchauffement, l'observation des amas de nickel se fait sous le microscope électronique à balayage. Les échantillons étudiés sont des réseaux 2D submicroniques de fils en niobium (pas du réseau 1-2 µm, largeur des fils 0.3 µm, épaisseur 0.2 µm) avec d'excellentes propriétés supraconductrices (température de transition 9.0K, RRR d'environ 30). Notre calcul de profil de champ magnétique au-dessus d'un réseau montre que le contraste entre cellules avec ou sans vortex est extrêmement faible. Suivant la hauteur au dessus du réseau, nous décorons soit les courants soit les milieux de cellules. La décoration se fait donc sur des réseaux planarisés, à des températures T<
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Duki, Solomon Fekade. "Topics in Hard and Soft Condensed Matter Physics." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1232737384.
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Mosconi, Paola. "Ghost Models in Two-Dimensional Condensed Matter Physics." Doctoral thesis, SISSA, 2003. http://hdl.handle.net/20.500.11767/4205.
Full textAbstract:
This thesis is devoted to the study of ghost theories out of the critical point, in two
dimensions.
The first chapter offers a bird's eye view of the most important applications of ghosts
to condensed matter physics. After a brief exposition of the basic (and less basic) facts
concerning ghosts at the critical point, an outline of the non-perturbative methods, used in
Part I and Part II, is furnished. Essentially, they rely on the so-called integrable approach,
which is based on the possibility of describing all the states of an integrable quantum field theory in terms of pseudo-particles in a Hilbert space. The scattering properties of such
excitations are encoded into a matrix (the S-matrix), which can be exactly determined by
imposing a set of stringent constraints, and which allows to specify completely the particle
content of the theory (masses, multiplicities, bound states) [38, 39]. The knowledge of the
scattering amplitude, then, permits to extract all the thermodynamic quantities of the system
(free energy) by means of the Thermodynamic Bethe ansatz (TBA) technique [40] and, at
least in principle, to determine the off-critical correlation functions of the local operators of
the theory, thanks to the so-called Form Factor bootstrap approach [41-43].
Part I contains the simplest examples of off-critical ghost theories, namely the massive
versions of the conformal free bosonic and fermionic ones [44]. Despite their non-interacting
nature, still there are non-local sectors of the models, which exhibit a highly interacting
behavior. Correlation functions of operators belonging to these sectors are computed exactly
and a comparison with the massive ordinary counterparts is performed. Afterwards, the
effects;produced by the introduction of impurities are considered [45]. At the moment, such
models lack a physical realization, but they are important as 'prototype' systems, shedding
light on some crucial basic aspects (e.g. the choice of the most convenient basis for the space
of states).
Part II deals with a deceptively simple representative of the aforementioned nonlinear
sigma models defined on supersymmetric manifolds, where the vector field, with one commuting
component and two anticommuting ones, transforms under the global symmetry
OSP(ll2). This system has a simple physical realization in terms of a dense loop model,
where crossings of loops are allowed [28, 46]. At long wavelength, the theory is gapless and
the Goldstone excitations are nothing but free fermionic ghosts [25, 28]. We propose the
exact S-matrix for this system and present TBA calculations, supporting such conjecture.
The bootstrap form factor approach is outlined, including a detailed discussion about the
symmetry properties of the model and the explicit derivation of some basic objects, such as
the minimal form factors. Moreover, we compute explicitly the two-point correlation function
of a suitably chosen operator of the theory, comparing its large distance limit with the
result expected on the basis of conformal field theory considerations. Since the work is still
in progress [47], we conclude sketching the main goals and the route we intend to take, in
order to pursue them.
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Woo, Jung Min. "Two mathematical problems in disordered systems." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/289124.
Full textAbstract:
Two mathematical problems in disordered systems are studied: geodesics in first-passage percolation and conductivity of random resistor networks. In first-passage percolation, we consider a translation-invariant ergodic family {t(b): b bond of Z²} of nonnegative random variables, where t(b) represent bond passage times. Geodesics are paths in Z², infinite in both directions, each of whose finite segments is time-minimizing. We prove part of the conjecture that geodesics do not exist in any fixed half-plane and that they have to intersect all straight lines with rational slopes. In random resistor networks, we consider an independent and identically distributed family {C(b): b bond of a hierarchical lattice H} of nonnegative random variables, where C(b) represent bond conductivities. A hierarchical lattice H is a sequence {H(n): n = 0, 1, 2} of lattices generated in an iterative manner. We prove a central limit theorem for a sequence x(n) of effective conductivities, each of which is defined on lattices H(n), when a system is in a percolating regime. At a critical point, it is expected to have non-Gaussian behavior.
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Posavec, Tony. "An Investigation into the Fluorescence of Polymers." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1499353221343727.
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Varea, Emilien. "Experimental analysis of laminar spherically expanding flames." Phd thesis, INSA de Rouen, 2013. http://tel.archives-ouvertes.fr/tel-00800616.
Full textAbstract:
Laminar burning velocity is very useful for both combustion modeling and kinetic scheme validationand improvement. Accurate experimental data are needed. To achieve this, the spherical flame method was chosen. However various expression for burning velocity from the spherically expanding flame can be found. A theorical review details all the expressions and models for the burning veolcity and shows how they can be obtained experimentally. These models were comparated considering basic fuels - various Lewis numbers. As a result, it is shown that the pure kinematic measurement method is the only one thet does not introduce any assumptions. This kinematic measurement had needed the development and validation of an original post-processing tool. Following the theorical review, a parametric experimental study is presented. The new technique is extended to extract burning velocity and Markstein length relative to the fresh gas for pure ethanol, isooctane and blended fuels at high pressure.
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Jung, Young Woo. "Optical studies and biological applications of spins in semiconductors." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1306523724.
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Babadi, Mehrtash. "Non-equilibrium dynamics of artificial quantum matter." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11114.
Full textAbstract:
The rapid progress of the field of ultracold atoms during the past two decades has set new milestones in our control over matter. By cooling dilute atomic gases and molecules to nano-Kelvin temperatures, novel quantum mechanical states of matter can be realized and studied on a table-top experimental setup while bulk matter can be tailored to faithfully simulate abstract theoretical models. Two of such models which have witnessed significant experimental and theoretical attention are (1) the two-component Fermi gas with resonant $s$-wave interactions, and (2) the single-component Fermi gas with dipole-dipole interactions. This thesis is devoted to studying the non-equilibrium collective dynamics of these systems using the general framework of quantum kinetic theory.Physics
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De, Silva Theja Nilantha. "Spin-Orbital Physics in Transition Metal Oxides." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1092948911.
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Pike, Nicholas A. "Energy Dispersion, Magnetism, and Transport in Three Condensed Matter Systems." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417604062.
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Smith, Gregory J. "Application of Attosecond Techniques to Condensed Matter Systems." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1608496995249541.
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