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 21 for “"Quantum oscillations"”.
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Quantum oscillations in Dirac semimetals
… structure and its corresponding Fermi surface, quantum oscillations have proven very useful as they provide a tool to directly measure the Berry phase under certain conditions. The (double) Dirac semimetal NbTe₄ has shown the occurrence of multiple charge-density-wave (CDW) phases, and as a …
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Fermi Surfaces and Where to Find Them: Quantum Oscillations in Kondo Insulators and High-Temperature Superconductors
… physical properties of metals, and have made quantum oscillations, the experimental manifestation of the Fermi surface, a hallmark signature of metals. In this thesis we have studied systems that are distinctly non-Fermi liquid, and discovered that, contrary to this canon, quantum oscillations …
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EXPERIMENTAL STUDIES OF QUANTUM OSCILLATIONS IN THE TRANSVERSE MAGNETORESISTANCE OF SINGLE-CRYSTALLINE, ULTRAPURE MAGNESIUM: NON-OHMIC EFFECTS.
… to investigate the low current regime where the oscillations appear to satisfy Ohm's Law. A superconducting chopper amplifier was built which had the sensitivity to measure 10⁻¹¹ volt signals. We present evidence which directly relates this non-ohmic behavior to the long-range influence of a …
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High magnetic field quantum oscillation study of Fermi surfaces in bulk unconventional insulators
… searching for other examples of unconventional quantum oscillatory insulators. Following SmB6, two additional strongly correlated insulators have been found to display insulating quantum oscillations: YbB12 and FeSb2. YbB12 is an f-electron Kondo insulator, much like SmB6, and exhibits similar …
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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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Unconventional Fermi surface in insulating SmB6 and superconducting YBa2Cu3O6+x probed by high magnetic fields
… magnetic fields up to 45 T, while prominent quantum oscillations in magnetisation are observed above 10 T. Angular dependence of the quantum oscillations revealed a three-dimensional characteristics with an absolute amplitude consistent with a bulk origin, and temperature dependence showed a …
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High magnetic field study of strongly correlated electron systems
… transition and superconductivity. Observation of quantum oscillations in the presence of a strong magnetic field is a signature of Fermi liquid behaviour and can be used in conjunction with complementary experimental techniques to map the Fermi surface of a metal. For metallic states, the Fermi …
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New features in the phase diagrams of the cuprate high-Tc superconductors mapped using strong magnetic fields
… temperatures, we reveal an unconventional quantum vortex matter ground state hosting quantum oscillations. This vortex matter ground state is highly resilient to applied magnetic field, but fragile to applied temperature and current. It is characterised by vanishing electrical resistivity, …
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Geometry and Topology of Quantum States in Quasicrystalline Systems
… picture, we find the presence of Bloch oscillations, usually synonymous with periodicity, alongside additional anomalous terms due to Berry curvature contributions. Fascinatingly, we also discover a so-called spiral holonomy in the effective band structure, in which circular trajectories …
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Quantum oscillation studies in the unconventional superconductor YFe₂Ge₂ and in the Dirac semimetal candidates NbXSb (X = Ge/Si)
… possibly connected to its vicinity to a quantum critical point. The materials NbXSb (X = Ge/Si) have been theoretically predicted via initial density functional theory (DFT) calculations to harbour Dirac/Weyl-like features in their electronic band structure. Quantum oscillations were …
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Quantum Transport and Electric-Field Effects in Layered Topological Semimetals and Magnetic Materials
… dissertation describes transport experiments on quantum devices in layered Dirac nodal line topological semimetals and antiferromagnetic materials down to a few layers. We used gate-induced effects to alter the transport properties of these materials. </p> <p>First, we introduced current …
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FeSb2: a riddle, inside an insulator, wrapped in a metal Electric and magnetic properties of the unconventional insulator iron diantimonide
… Under the application of high magnetic fields, quantum oscillations in the magnetisation are observed, with an inverse-field periodicity indicating the presence of Landau quantisation. Remarkably, these are shown to emanate from the insulating bulk of the material – in sharp contrast to our …
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Transport and thermodynamic studies of the superconductors A3T4Sn13 and YFe2Ge2
Materials in proximity to quantum critical points (QCPs) experience strong fluctuations in the order parameter associated with the transition and often, as a result, display interesting properties. In this dissertation, we have used a variety of experimental probes such as Shubnikov-de Haas quantum …
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Correlated low temperature states of YFe2Ge2 and pressure metallised NiS2
… due to proximity to an antiferromagnetic quantum critical point (QCP). Existence of the latter is also indicated by the non-Fermi liquid T$^{3/2}$ behaviour of the low temperature resistivity. Below 1.8 K a superconducting phase develops in the material, making it a rare case of a …
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Experimental Observation of Geometric Phases in Narrow-Gap Semiconductor Heterostructures
We have studied the electron quantum phase by fabricating low dimensional (d ≤ 2) mesoscopic interferometers in high-quality narrow-gap semiconductor (NGS) heterostructures. The low effective-mass electrons in NGS heterostructures enable observation of delicate quantum phases; and the strong …
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Thermoelectric properties of mesoscopic systems in GaAs
… (2DMSs) and antidot lattices defined in them. Quantum oscillations in the thermopower (TP) of a quantum point contact allow accurate determination of the local electron temperature. The low temperature (T < 0.3 K) TP of square (5 ?m x 5 ?m) mesoscopic devices shows a highly enhanced value, …
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Periodically Modulated Electronic States in Natural Superlattices
… non-trivial bands for M = Nb and unusual quantum oscillations for M = Ta, these materials also host unconventional correlated states; we observe long-anticipated signatures of 2D Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductivity for M = Nb and preliminary evidence for a correlated …
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Unconventional Superconductivity in the Layered Iron Germanide YFe2Ge2
… with theoretical predictions. Moreover, quantum oscillations have been detected for the first time in dHvA susceptibility and tunnel-diode oscillation measurements of high-quality YFe$_2$Ge$_2$ single crystals. Although unable to account fully for the high Sommerfeld coefficient, the …
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MICROWAVE STUDY OF THE PROPERTIES OF UNCONVENTIONAL SUPERCONDUCTING SYSTEMS
… such as transport resistivity measurement, quantum oscillations in electrical resistance and magnetic susceptibility, scanning tunneling microscopy, optical frequency techniques, X-ray, angle-resolved photoemission spectroscopy, and Raman spectroscopy. On the other hand, microwave …
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High Pressure Quantum Oscillation Study of BiTeI and Bi2Te3
… under pressure. Using Shubnikov-de Haas quantum oscillation measurements, the evolution of the Fermi surface of both materials was tracked as a function of pressure. At ambient pressure, two distinct quantum oscillation frequencies in BiTeI, corresponding to inner and outer Fermi surface …
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