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Electric Transport of Rare-earth Metal Oxy-hydride Thin FilmsKazi, Suraya January 2021 (has links)
In this project, I investigate the photoconductivenature of photochromic rare-earth metal oxy hydrides (REMHO). Such materials have received increasingscientific attention since they show a color-neutralphotochromic effect that can be applied, e.g., in smartwindows or chromogenic devices. Photochromicmaterials reversibly turn opaque from transparentunder illumination with light of optical wavelength. Inrecent studies it was found that these materials alsoshow an instant decrease in resistivity whenilluminated which can be used in optical sensors. Tounderstand the nature of this photoconductive effect,I grew yttrium oxy hydride thin films by reactivemagnetron sputtering. I measured the resistivity forillumination from front and substrate side, opticaltransmission and compositions of the samples andrelated the results to photoconductivity. I show thatphotoconductivity is a bulk effect and not directlyrelated to photochromism. Samples that almost lostphotochromism due to aging, still show strongphotoconductivity. Moreover, it was observed that theresistance increased faster during bleaching for frontillumination than for back illumination.
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From electronic correlations to higher-order topology in nodal Fermi liquidsSzabó, András László 23 March 2022 (has links)
In this thesis we study a variety of two- and three-dimensional (2D and 3D, respectively) nodal semimetals, subjected to local electronic interactions or disorder. Such systems constitute a minimal model for various real materials and capture a plethora of interesting physical phenomena therein. Our methodology includes an unbiased renormalization group analysis controlled by epsilon expansions about the appropriate lower critical dimension, mean-field analysis, as well as complementary numerical analyses. First, we focus on emergent symmetries at various infrared unstable quantum critical points, appearing in a renormalization group flow of interaction couplings. We investigate a 3D chiral Dirac semimetal, which in a noninteracting system enjoys a microscopic U(1)⊗SU(2) global symmetry. Though the chiral symmetry is absent in the interacting model, it gets restored (partially or fully) at various fixed points as emergent phenomena. Subsequently, we study a collection of 3D interacting effective spin-3/2 biquadratic Luttinger fermions, and demonstrate the emergence of full rotational symmetry between the distinct nematic sectors (namely Eg and T2g ) of the corresponding octahedral group. We then investigate the effects of electronic interactions at zero and finite temperature and chemical doping in a collection of (i) 2D Dirac and Luttinger fermions, constituting the linearly and quadratically dispersing low-energy excitations in monolayer and bilayer graphene, respectively, and (ii) 3D Luttinger fermions, describing a biquadratic touching of Kramers degenerate conduction and valence bands, relevant in the normal state of 227 pyrochlore iridates, and half-Heusler compounds, for example. These systems exhibit a plethora of competing broken symmetry phases (both magnetic and superconducting) when tuning the strength of interactions, temperature, and chemical doping. In this context we propose the selection rules, identifying the broken symmetry phases promoted by a given interaction channel, and the organizing principle, ordering these preselected phases along the temperature axis based on a generalized energy-entropy argument. Finally, we explore topological aspects of nodal Fermi liquids. We propose an experimentally feasible way to engineer higher-order topological phases via the application of uniaxial strain on a 3D Luttinger semimetal. Favoring a direction, strain explicitly breaks cubic symmetry. We show that the corresponding nematic orderings of Luttinger fermions result in a topological insulator or Dirac semimetal, depending on the sign (compressive or tensile, respectively) of the strain. We show that both of these phases host 1D hinge modes, localized along the edges parallel to the direction of strain, that are therefore second-order topological in nature. We then investigate the effects of disorder on such a second-order Dirac semimetal, and show its stability for weak enough disorder. At a critical disorder strength the system goes through a quantum phase transition into a diffusive metal phase and the toplogical hinge states melt into the bulk. The methodology presented in this thesis can be extended to a large family of correlated multiband systems, such as Weyl and nodal-loop semimetal. Read more
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Hydrogen Isotope Separation in Metal-Organic FrameworksZhang, Naiyuan 10 December 2018 (has links)
No description available.
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Electronic and Spin Dependent Phenomena in Two-Dimensional Materials and HeterostructuresXu, Jinsong 03 December 2018 (has links)
No description available.
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Role of Chemical Surface Preference in Translational and Reorientational NanoconfinementGuo, Hao 28 September 2018 (has links)
No description available.
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Studies on Electron Dynamics in Deformed GrapheneZhai, Dawei January 2018 (has links)
No description available.
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A Two-dimensional Semiconducting GaN-based Ferromagnetic MonolayerMa, Yingqiao January 2018 (has links)
No description available.
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Controlling Anisotropy in Organic-Based Magnets for Coherent MagnonicsChilcote, Michael A. 29 August 2019 (has links)
No description available.
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Manipulation of Molecular Charge Density Waves and Molecular Transport SystemsLatt, Kyaw Zin 23 September 2019 (has links)
No description available.
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Magnetic Resonance Detection using Nitrogen-Vacancy Centers in DiamondPurser, Carola Midori 02 October 2019 (has links)
No description available.
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