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Articles 1 - 9 of 9
Full-Text Articles in Physics
Quantum Phase Transitions In Disordered Boson Systems, Zhiyuan Yao
Quantum Phase Transitions In Disordered Boson Systems, Zhiyuan Yao
Doctoral Dissertations
In this dissertation, we study the superfluid-insulator quantum phase transition in disordered boson systems. Recently, there has been considerable controversy over the validity of the scaling relations of the superfluid--Bose-glass quantum phase transition in three dimensions. Results from experimental and numerical studies on disordered quantum magnets contradict the scaling relations and the associated conventional scaling hypothesis for the singular part of the free energy. We determine various critical exponents of the superfluid--Bose-glass quantum phase transition in three-dimensional disordered Bose-Hubbard model through extensive Monte Carlo simulations. Our numerical study shows the previous studies on disordered quantum magnets were performed outside the …
Geometry, Growth And Pattern Formation In Thin Elastic Structures, Salem Al-Mosleh
Geometry, Growth And Pattern Formation In Thin Elastic Structures, Salem Al-Mosleh
Doctoral Dissertations
Thin shells are abundant in nature and industry, from atomic to planetary scales. The mechanical behavior of a thin shell depends crucially on its geometry and embedding in 3 dimensions (3D). In fact, the behavior of extremely thin shells becomes scale independent and only depends on geometry. That is why the crumpling of graphene will have similarities to the crumpling of paper. In this thesis, we start by discussing the static behavior of thin shells, highlighting the role of asymptotic curves (curves with zero normal curvature) in determining the possible deformations and in controlling the folding patterns. In particular, we …
Computational Modeling Of Defect-Engineered Graphene Derivatives And Graphene-Polymer Nanocomposites, Asanka Weerasinghe
Computational Modeling Of Defect-Engineered Graphene Derivatives And Graphene-Polymer Nanocomposites, Asanka Weerasinghe
Doctoral Dissertations
Graphene has unique mechanical, electronic, and thermal properties, which enable a broad range of technological applications. For example, graphene flakes can be used as filler to enhance the properties of polymer-matrix nanocomposites and graphene derivatives, generated by defect engineering and chemical functionalization of single-layer graphene, have tunable properties that are very promising for engineering electronic and thermomechanical metamaterials. A fundamental understanding of the structure-property relationships that govern the function of such nanocomposites and graphene derivatives is required for designing and developing future graphene-based metamaterials. Toward this end, we have conducted a systematic study based on extensive molecular-dynamics simulations of mechanical …
Combined Spectroscopic And Scanning Probe Studies Of Electronic Interactions In Nanostructured 1d And 2d Semiconductors, Peijian Wang
Combined Spectroscopic And Scanning Probe Studies Of Electronic Interactions In Nanostructured 1d And 2d Semiconductors, Peijian Wang
Doctoral Dissertations
This dissertation includes the exploration about the following research questions: 1. What is the correlation between the work function and ground state interactions in organic semiconductor assemblies? 2. How do non-covalent chemical doping tune the work function in MoS2? 3. Are there surface charges in the Aluminum doped ZnO nanocrystals (AZO) and what's the evolution of the surface charges and polarizabilities from undoped AZO to doped AZO? 4. How is the homogeneity like during doping in the organic thermoelectric materials? The techniques we employed in the research is the spatially registered Kelvin Probe Force Microscopy and Photoluminescence spectroscopy …
Antenna Enhanced Graphene Terahertz Emitter And Detector, And Graphene Microwave Detector, Jiayue Tong
Antenna Enhanced Graphene Terahertz Emitter And Detector, And Graphene Microwave Detector, Jiayue Tong
Doctoral Dissertations
Graphene is a promising candidate for optoelectronic and fast electronics research. In THz and sub-THz frequency regime, sensitive detectors are very difficult to make. This dissertation presents my Ph.D study of THz sources and THz/Microwave (MW) detectors made with graphene. My work demonstrates the emission and detection of 1.9 THz radiation from graphene coupled to a double-patch antenna and a silicon lens. More than 3 orders of magnitude performance improvements are achieved in a half-edge-contacted graphene thermoelectric (TE) detector operating at 1.9 THz by antenna coupling and Si lens coupling. The thermoelectric mechanism is also employed in MW detection. A …
Complex Ground States Of Vortices And Filaments, Qingyou Meng
Complex Ground States Of Vortices And Filaments, Qingyou Meng
Doctoral Dissertations
This dissertation consists of two parts. In the first part, we studied the ground state configurations of vortices with multi-scale inter-vortex interactions in layered superconductors. We found that by tuning the multi-scale interaction length, we could create vortex lattice ground states with different symmetries. It has been proposed that these structures can trap ultra-cold atoms for use in quantum emulators. In further work, we measured the phase diagram and discovered many new phases by changing the relative magnitude of the interaction ranges. In the second part, we analyzed the ground state configurations of confined filaments with long-range repulsive interactions. We …
First-Principle Approaches To Strongly Correlated Quantum Spin Systems, Yuan Huang
First-Principle Approaches To Strongly Correlated Quantum Spin Systems, Yuan Huang
Doctoral Dissertations
My Ph.D. research focuses on the numerical study of two quantum spin systems, one is the square-lattice Heisenberg antiferromagnet with ring-exchange interaction at the Neel to valence-bond solid state transition, which is proposed to be described by the theory of deconfined criticality; the other is the highly frustrated pyrochlore Heisenberg antiferromagnet. Both systems are known as prototypical candidates for the exotic spin-liquid state with emergent fractionalized excitations and gauge structure. Regarding the long standing controversy of deconfined criticality, our results conclude that the deconfined critical theory capture the essence of the Neel to valence-bond solid state transition at least at …
Emergent Phenomena In Quantum Critical Systems, Kun Chen
Emergent Phenomena In Quantum Critical Systems, Kun Chen
Doctoral Dissertations
A quantum critical point (QCP) is a point in the phase diagram of quantum matter where a continuous phase transition takes place at zero temperature. Low-dimensional quantum critical systems are strongly correlated, therefore hosting nontrivial emergent phenomena. In this thesis, we first address two decades-old problems on quantum critical dynamics. We then reveal two novel emergent phenomena of quantum critical impurity problems. In the first part of the thesis, we address the linear response dynamics of the $(2+1)$-dimensional $O(2)$ quantum critical universality class, which can be realized in the ultracold bosonic system near the superfluid (SF) to Mott insulator (MI) …
Vibrated Squares As Equilibrium And Active Matter, Lee Askew Walsh
Vibrated Squares As Equilibrium And Active Matter, Lee Askew Walsh
Doctoral Dissertations
We study the effects of particle shape and self-propulsion on the collective behaviors of a two-dimensional granular fluid, using an experimental system of hard square grains. We energize the system by vibration, which, depending on particle shape, induces either isotropic diffusion or persistent self-propulsion in the particles. We use specially designed grains as a model system to study (i) the equilibrium packing of hard squares in two dimensions, (ii) the dynamics of athermal self-propelled particles, and (iii) the melting kinetics of an unconfined granular crystallite. The first study concerns the phase diagram of a two-dimensional fluid of hard squares, which …