Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 49 for “"Quantum Phase Transitions"”.
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Quantum phase transitions in disordered magnets
… study the effects of quenched weak disorder on quantum phase transitions in disordered magnets. The presence of disorder in the system can lead to a variety of exotic phenomena, e.g., the smearing of transitions or quantum Griffiths singularities. Phase transitions are smeared if individual …
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Disorder at first-order classical and quantum phase transitions
… the effects of quenched disorder on classical, quantum and nonequilibrium phase transitions. After a short introduction which covers the basic concepts of phase transitions, finite-size scaling and random disorder, the dissertation focuses on four separate but related projects. First, we …
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Pressure Induced Quantum Phase Transitions in Metallics Oxides and Pnictides
Quantum phase transitions occur as a result of competing ground states. The focus of the present work is to understand quantum criticality and its consequences when the competition is between insulating and metallic ground states. Metal-insulator transitions are studied by means of electronic …
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Quantum phase transitions in the presence of disorder and dissipation
<p>"A quantum phase transition is a phase transition at absolute zero occurring under variations in an external non-thermal parameter such as magnetic field or pressure. Quantum phase transitions are one among the important topics currently investigated in condensed matter physics. They are …
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Two-dimensional superconducting states near zero temperature quantum phase transitions
… decades. In two dimensions, only two electronic phases are predicted to exist at zero temperature – superconducting and insulating. Contrary to this theoretical expectation, previous transport measurements on 2-dimensional (2D) thin films have found evidence for metallic resistivity down to …
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Effective action approach to quantum phase transitions in bosonic lattices
… a new, field-theoretic method for describing the quantum phase transition between Mott insulating and superfluid states observed in bosonic optical lattices. I begin by adding to the Hamiltonian of interest a symmetry breaking source term. Using time-dependent perturbation theory, I then expand …
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Studies on the effect of noise in boundary quantum phase transitions
<p>Boundary quantum phase transitions are abrupt ground state transitions triggered by the change of the boundary conditions at single or multiple (but finite) points.</p><p>When boundary effects dominate, understanding boundary quantum phase transitions requires a deeper knowledge of strongly …
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Computational studies of thermal and quantum phase transitions approached through non-equilibrium quenching
Phase transitions and their associated critical phenomena are of fundamental importance and play a crucial role in the development of statistical physics for both classical and quantum systems. Phase transitions embody diverse aspects of physics and also have numerous applications outside physics, …
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Inelastic light scattering studies of quantum phase transitions in CuxTiSe2 and multiferroic TbMnO3
… probe the temperature- and magnetic-field-induced phase transitions of two strongly correlated systems – the magnetoelectric multiferroic TbMnO3 and the layered dichalcogenide TiSe2 . In general, strongly correlated materials have a strong coupling between charge, spin, lattice and orbital degrees …
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Quantum Entanglement: Geometric Quantification and Applications to Multi-Partite States and Quantum Phase Transitions
The degree to which a pure quantum state is entangled can be characterized by the distance or angle to the nearest unentangled state. This geometric measure of entanglement is explored for bi-partite and multi-partite pure and mixed states. It is determined analytically for arbitrary two-qubit …
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Quantum Entanglement: Geometric Quantification and Applications to Multi-partite States and Quantum Phase Transitions
The degree to which a pure quantum state is entangled can be characterized by the distance or angle to the nearest unentangled state. This geometric measure of entanglement is explored for bi-partite and multi-partite pure and mixed states. It is determined analytically for arbitrary two-qubit …
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Inelastic Light Scattering Studies of Quantum Phase Transitions in Copper Titanium Diselenium and Multiferroic Terbium Manganese Trioxygen
… focus of this dissertation is the study of quantum phase transitions in TiSe2 as a function of temperature and Cu-intercalation, and the comparison of the effects of intercalation and pressure on the charge-density-wave (CDW) order in this system. All these parameters---temperature, pressure …
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Magnetic and superconducting quantum critical behavior of itinerant electronic systems
"Quantum phase transitions occur at zero temperature as a function of some non-thermal parameter, e.g., pressure or chemical composition. In addition to being of fundamental interest, quantum phase transitions are important because they are believed to underlie a number of interesting low …
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An Exploration of Quantum Critical Phenomena in One-Dimensional Lattice Systems: Geometric Frustration & Quantum Fluctuations
… of critical phenomena within one-dimensional quantum lattice spin systems. People are exposed to classical critical phenomena everyday in the form of phase transitions, such as from water to ice. Surrounding quantum phase transitions, there is a number of exciting phenomena still to be …
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Exact diagonalization study of strongly correlated topological quantum states
A rich variety of phases can exist in quantum systems. For example, the fractional quantum Hall states have persistent topological characteristics that derive from strong interaction. This thesis uses the exact diagonalization method to investigate quantum lattice models with strong interaction. …
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Quasiparticles in Quantum Many-Body Systems
Topologically ordered phases flamboyance a cornucopia of intriguing phenomena that cannot be perceived in the conventional phases including the most striking property of hosting anyon quasiparticles having fractional charges and fractional statistics. Such phases were discovered with the remarkable …
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Realizing quantum spin models with ⁷Li atoms in an optical lattice
Quantum spin Hamiltonians are paradigmatic models, which display different kinds of quantum phase transitions, strongly-correlated and topological ground states, and various regimes of transport. Expanding their significance, many mappings exist between quantum spin models and other systems in …
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Modelling of Berry phase and Fermi-level topologies for emergent quantum phenomena prediction in selected solid state systems
… against perturbations and offer routes to novel quantum functions. This thesis investigates three representative compounds - SrSi2, CoSi, and NbP - to reveal how external stimuli, namely tensile strain and electric fields, tune their electronic bands and topological traits. By combining …
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Aspects of Quantum Fluctuations under Time-dependent External Influences
The vacuum of quantum field theory is not empty space but filled with quantum vacuum fluctuations, which give rise to many intriguing effects. The first part of this Thesis addresses cosmic inflation, where the quantum fluctuations of the inflaton field freeze and get amplified in the expanding …
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