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 60 for “"quantum critical"”.
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Superconductivity in the proximity of a quantum critical point
… to absolute zero can result in a low temperature quantum fluid which deviates strongly from typical metallic behaviour; unconventional superconductivity can be induced by the strange metal region surrounding the zero-temperature phase transition. In this thesis we focus on three systems which …
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Electrical transport and superconductivity in doped quantum critical ferroelectrics
… transport and superconductivity in doped quantum critical ferroelectrics) presents the results of research into the electrical transport and superconductivity found in the neighbourhood of quantum phase transitions in carrier-doped ferroelectrics and paraelectrics. The materials of …
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Quantum critical matter: Casimir pairing, emergent orders and topological defects
In this thesis we address a few problems on critical phenomena in two- and three dimensional quantum materials. Specifically we consider high temperature superconductors, dimerized quantum magnets and frustrated magnets. First, motivated by the recent discovery of a magnetic quantum critical point …
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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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Quantum Critical Ferroelectricity and Emergent Phenomena in KTaO3 and SrTiO3
This thesis explores the quantum phase diagrams of KTaO3 and SrTiO3, both quantum paraelectrics near to a ferroelectric quantum critical point, including study of material properties which may be influenced by proximity to a ferroelectric quantum phase transition. A quantum critical phase …
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An Exploration of Quantum Critical Phenomena in One-Dimensional Lattice Systems: Geometric Frustration & Quantum Fluctuations
… thesis focuses on identifying different types 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 …
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Low-Energy Effective Field Theories for the Antiferromagnetic Quantum Critical Metal with Z2, O(2) and O(3) spin symmetries
… the low-energy physics of the antiferromagnetic quantum critical metal. In the first part of the thesis, we study the dynamics of critical spin fluctuations and hot electrons at the metallic antiferromagnetic quantum critical points with Z2 and O(2) spin symmetries, building upon earlier works on …
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Aspects of quantum criticality in itinerant electron ferromagnetic systems
… This thesis is mainly concerned with such quantum critical points and is an investigation into the various phenomena seen in the phase diagram of itinerant ferromagnetic systems. We apply a standard theory of itinerant quantum criticality to a quantum-critical end-point in a …
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Quantum Tuning and Emergent Phases in Charge and Spin Ordered Materials
… any tuning in the proximity of a ferroelectric quantum critical point. This work presents the first high-precision dielectric measurements under hydrostatic pressure carried out on a quantum critical ferroelectric, leading to a full pressure-temperature phase diagram for SrTiO$_3$. The influence …
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Unconventional Superconductivity in Uranium Ditelluride
… UTe2 exhibits extremely high upper critical fields of up to 70 Tesla, minimal change in the local spin susceptibility upon the crossing superconducting transition temperature, and a remarkable phase diagram comprising multiple distinct superconducting phases intertwined with complex …
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Two-particle level diagrammatic approaches for strongly correlated systems
… FLEX or SOPT and a satisfactory agreement with Quantum Monte Carlo results despite instabilities in the self-consistency at low temperatures and for strong Coulomb interaction. We use the parquet formalism to study the Quantum Critical Point at finite doping in the Hubbard model by decomposing …
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Competition and unification of Kondo coherence and magnetic ordering
The heavy fermion quantum critical point is one of the most puzzling problems in the field of highly correlated electrons. This is a quantum critical point separating a non-magnetic heavy fermi liquid metal from an antiferromagnetically ordered metal. The major problem facing us is the fact that, …
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A study of holographic superconductors
The proposal that the physics of quantum critical phase transition in strongly coupled condensed matter systems can be described by a gravitational theory within the frame work of gauge/gravity correspondence is investigated more extensively for s-wave superconductors. We consider a gravitational …
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Hybridized Criticality and Elementary Excitations in LiHoF4
… the magnetic properties of LiHoF<sub>4</sub>. Quantum criticality in rare earth ferromagnet LiHoF<sub>4</sub> is complicated by the presence of strong crystal field and hyperfine interactions resulting, e.g., in incomplete mode softening reported by Rønnow et al. We construct a systematic …
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Magnetic Penetration Depth Analysis of Unconventional Superconductors
… of antiferromagnetism and the presence of a quantum critical point on superconductivity. We also seek to characterize the superconductivity and compare to similar materials. Additionally we seek to study how superconductivity arises from novel methods such as charge density waves.
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Field-induced magnetic phase transitions and correlated electronic states in the hexagonal RAgGe and RPtIn series
… fermion compounds, with a magnetic field-induced quantum critical point QCP. In the former compound, a non-Fermi liquid-like NFL regime is apparent at intermediate fields, but such a behavior is more ambiguous in the YbPtIn. However, a small Pt-deficiency in flux-grown YbPt0.98In single crystals …
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Insulator-Superconductor Transitions in Two Dimensions
… consider the fluctuation conductivity near the quantum critical point (QCP) in the presence of dissipation. We show that sufficiently close to the QCP, Ohmic dissipation can change the dynamical critical exponent from z = 1 to z = 2 in the quantum critical (QC) regime. In the third part we show …
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High-Pressure Studies of Some Heavy Fermion Materials
… work, such as unconventional superconductivity, quantum critical points and quantum oscillations, and I explain why heavy fermion materials under pressure are good systems for studying these effects. Chapter 2 describes the experimental techniques used in my measurements. I give an overview of …
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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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High pressure studies of superconductivity and anomalous normal states in novel quantum materials
… parameters for accessing or tuning away from the quantum critical point but also to enter novel phases that cannot usually be found in any materials at ambient conditions. Sb (Chapter 4): High-pressure phase Sb-II exhibits a novel incommensurate host-guest structure, giving rise to exotic sliding …
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