+publisher:"Brown University" +contributor:("Kosterlitz, John")

1. YU, LICHAO. Defects in Two Dimensional Colloidal Crystals.

Degree: PhD, Physics, 2015, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:419422/

We use digital video microscopy to study the defects in two-dimensional colloidal crystals (2DCC). A crystalline solid, different from its liquid state, preserves long-wavelength shear rigidity and broken symmetry. Questions about how shear rigidity and long-range order disappear during melting, are unresolved in terms of the complication of defect structures and their roles in crystal melting, especially in two dimension. Colloidal crystals (CC) serve as a promising model system to directly observe the defects under optical microscope. In our first study, we report the effects of vacancies and interstitials on the phonon modes in a 2DCC. By applying the equipartition theorem, we extract the dispersion relation of the lattice vibrations using real-time video microscopy. We find that both longitudinal and transverse modes in the spectrum are softened by the existence of point defects. Second, we investigate the diffusion process of interstitials in a 2DCC. The motion is viewed as gliding of both edge dislocations along one of the crystalline axes. The microscopic process is equivalently a point mass overcoming Peierls barrier with an exponential escaping time. We also establish a new criterion to determine the ergodicity of a defect system and discover the nonergodic behavior of di-interstitials. Advisors/Committee Members: LING, XINSHENG (Director), KOSTERLITZ, JOHN (Reader), PELCOVITS, ROBERT (Reader).

Subjects/Keywords: Defects

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APA (6^th Edition):

YU, L. (2015). Defects in Two Dimensional Colloidal Crystals. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:419422/

Chicago Manual of Style (16^th Edition):

YU, LICHAO. “Defects in Two Dimensional Colloidal Crystals.” 2015. Doctoral Dissertation, Brown University. Accessed January 26, 2021. https://repository.library.brown.edu/studio/item/bdr:419422/.

MLA Handbook (7^th Edition):

YU, LICHAO. “Defects in Two Dimensional Colloidal Crystals.” 2015. Web. 26 Jan 2021.

Vancouver:

YU L. Defects in Two Dimensional Colloidal Crystals. [Internet] [Doctoral dissertation]. Brown University; 2015. [cited 2021 Jan 26]. Available from: https://repository.library.brown.edu/studio/item/bdr:419422/.

Council of Science Editors:

YU L. Defects in Two Dimensional Colloidal Crystals. [Doctoral Dissertation]. Brown University; 2015. Available from: https://repository.library.brown.edu/studio/item/bdr:419422/

2. Yang, Guang. Topological Order in Superconductors and Quantum Hall Liquids.

Degree: PhD, Physics, 2014, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:386208/

Fractional quantum Hall (FQH) liquids are interesting two-dimensional electron systems that possess quasiparticle excitations with fractional charges, obeying quantum statistics different from those of bosons and fermions. In particular, the FQH liquid at filling factor 5/2 was proposed to host Majorana bound state (MBS) with exotic non-Abelian statistics. A collection of MBSs can span a topological Hilbert space, in which each many-particle state is topologically distinct, depending on the historical trajectories of all the MBSs in the system. Logic operations in quantum computation can be encoded in the linear transformations in topological Hilbert space and in principle be protected against local defects and perturbations, which are topologically trivial and cannot induce transitions between different many-particle states. Despite such intriguing theoretical picture, experiments probing the nature of the 5/2 FQH liquid are controversial. In this dissertation, we provide an explanation of two seemingly contradicting experiments in the 5/2 FQH liquid, by exploring the role of electrostatic interaction closely related to the geometries of the devices. We also construct several new 5/2 FQH states, by making use of the particle-hole symmetry in FQH systems, to account for a recent experiment observing upstream neutral edge transport in the 5/2 FQH liquid, which ruled out most of the existing theories. In addition to the new particle-hole states, we propose another topological description of the 5/2 FQH liquid which reconciles all existing transport experiments. Later, we turn our attention to the MBSs in superconductor systems. We study the approaches to minimizing the decoherence of a Majorana-fermion-based qbit due to its interaction with environment, based on a full classification of the fermionic zero modes in a system of interacting Majorana fermions. Advisors/Committee Members: Feldman, Dmitri (Director), Kosterlitz, John (Reader), Mitrovic, Vesna (Reader).

Subjects/Keywords: topological order

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Yang, G. (2014). Topological Order in Superconductors and Quantum Hall Liquids. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:386208/

Chicago Manual of Style (16^th Edition):

Yang, Guang. “Topological Order in Superconductors and Quantum Hall Liquids.” 2014. Doctoral Dissertation, Brown University. Accessed January 26, 2021. https://repository.library.brown.edu/studio/item/bdr:386208/.

MLA Handbook (7^th Edition):

Yang, Guang. “Topological Order in Superconductors and Quantum Hall Liquids.” 2014. Web. 26 Jan 2021.

Vancouver:

Yang G. Topological Order in Superconductors and Quantum Hall Liquids. [Internet] [Doctoral dissertation]. Brown University; 2014. [cited 2021 Jan 26]. Available from: https://repository.library.brown.edu/studio/item/bdr:386208/.

Council of Science Editors:

Yang G. Topological Order in Superconductors and Quantum Hall Liquids. [Doctoral Dissertation]. Brown University; 2014. Available from: https://repository.library.brown.edu/studio/item/bdr:386208/

3. Jin, Dafei. Studies of Electron Bubbles and Quantized Vortices in Superfluid Helium-4.

Degree: PhD, Physics, 2012, Brown University

URL: https://repository.library.brown.edu/studio/item/bdr:297710/

An electron injected into liquid helium strongly repels the surrounding helium atoms away due to the Pauli exclusion principle, and confines its own wavefunction inside a cavity about 2 nm in radius, called an electron bubble. Its interaction with the topological excitations in superfluid helium, namely, quantized vortices, has been a particularly attractive topic for several decades. The combination of a single electron and macroscopic condensed helium serves as a unique model system for us to study many fundamental questions on the border between classical and quantum mechanics. We first report our experiment on imaging single-electron bubble motion. Specifically, we used a strong enough planar transducer to expand electron bubbles to micron size in a large volume of the cell and trace their motion with a strong light source and a sensitive camera. A theoretical analysis on the origin of the electrons in helium due to cosmic rays is presented and some striking pictures showing bubble-vortex interactions are given. We then report our experiment on imaging micron-sized particle motion. We discuss the drag forces and the acoustic radiation forces in liquid helium and their actions on small particles. We show our observations of some particles very likely to be trapped and moving on quantized vortices, and some other objects exhibiting rather strange motions. Next, we introduce our time-dependent density functional simulations on single-electron bubbles. We display in the picosecond timescale how a fast-moving electron bubble experiences vortex nucleation and phonon radiation, and how an optically excited electron bubble undergoes shape distortion and fission at different pressures. Finally, we introduce our finite-element simulations on multi-electron bubbles, which are unique but fairly classical objects in liquid helium. We find that they are unstable at rest but can be stabilized by the Bernoulli pressure from the liquid if they are moving. Advisors/Committee Members: Maris, Humphrey (Director), Kosterlitz, John (Reader), Seidel, George (Reader).

Subjects/Keywords: electron bubble

Record Details Similar Records Cite « Share

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Jin, D. (2012). Studies of Electron Bubbles and Quantized Vortices in Superfluid Helium-4. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:297710/

Chicago Manual of Style (16^th Edition):

Jin, Dafei. “Studies of Electron Bubbles and Quantized Vortices in Superfluid Helium-4.” 2012. Doctoral Dissertation, Brown University. Accessed January 26, 2021. https://repository.library.brown.edu/studio/item/bdr:297710/.

MLA Handbook (7^th Edition):

Jin, Dafei. “Studies of Electron Bubbles and Quantized Vortices in Superfluid Helium-4.” 2012. Web. 26 Jan 2021.

Vancouver:

Jin D. Studies of Electron Bubbles and Quantized Vortices in Superfluid Helium-4. [Internet] [Doctoral dissertation]. Brown University; 2012. [cited 2021 Jan 26]. Available from: https://repository.library.brown.edu/studio/item/bdr:297710/.

Council of Science Editors:

Jin D. Studies of Electron Bubbles and Quantized Vortices in Superfluid Helium-4. [Doctoral Dissertation]. Brown University; 2012. Available from: https://repository.library.brown.edu/studio/item/bdr:297710/

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