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Online 41. Theory of fewphoton quantum scattering in nanophotonic structures [electronic resource] [2017]
 Xu, Shanshan.
 2017.
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The capability to create strong photonphoton interaction at a fewphoton level in integrated photonic systems is of central importance for quantum information processing. To achieve such a capability, an important approach is to confine photons in a onedimensional waveguide coupled to a local quantum system with strong nonlinearity. At a fundamental level, photonphoton interaction in such system is described by multiphoton scattering matrix (S matrix). In this thesis, we discuss both computational and conceptual aspects of multiphoton S matrix. For the computational aspect, we provide a systematical way to compute Nphoton S matrix using the inputoutput formalism. The main result is a general connection between the Nphoton S matrix and the Green functions of the local quantum system. Such computation can be generalized straightforwardly to the case of multiple waveguide channels to study the Fano interference in the presence of photonphoton interactions. For the conceptual aspect, we discuss the general structure of twophoton S matrix without explicit computation. Using techniques that are closely related to cluster decomposition principles in quantum field theory, we provide a general constraint on the analytic properties of the twophoton S matrix. Furthermore, we present a generalized form of the cluster decomposition principle. The twophoton S matrix, when the local quantum region supports multiple ground states, has an analytic structure that differs significantly from what is commonly anticipated.
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Online 42. Topological aspects of gapless phases [electronic resource] [2017]
 Bulmash, Daniel.
 2017.
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The development of topological phases of matter has greatly expanded our understanding of what a phase of matter could be. Topological phases have highly robust features; this robustness is typically protected by an energy gap. However, with the recent discovery of Weyl and Dirac semimetals, it has been realized that not only can gapless systems be topologically nontrivial, often with gaplessness itself being topologically protected. This thesis is a theoretical exploration of gapless topological phases from several perspectives. First, we propose that Hg_{1xy}Cd_xMn_yTe can be a timereversalbroken WSM. This proposal has several benefits, including that the singledopant (x=0 or y=0) cases are already very wellstudied, the Weyl points are tunable using magnetic field, and the Hall conductivity behaves highly nontrivially as a function both of temperature and of magnetic field angle. Next, we investigate WSM and DSM thin films, looking for quantum oscillations that involve the Fermi arcs. We extend known results in the weakfield limit, and propose a new experiment with a strong inplane component in the field which has highly unusual dependence of the quantum oscillations on field angle. Inspired by the ensuing theoretical understanding of a 3D metal in a strong magnetic field, we then investigate the effect of interactions on metallic wires subject to the orbital effects of a strong magnetic field. Using an analogy between fermions in the zeroth Landau level and truly 1D fermions with a (potentially large) pseudospin, we are able to apply powerful 1D tools like bosonization to find a plethora of interesting phases. This includes phases where the correlation functions of either charge density wave order or superconducting order obey magnetic fieldtuned power laws, as well as a phase with power law correlations of both pseudospintriplet superconductivity and pseudospindensity wave order. Finally, we construct a framework for unifying the topological response properties of both gapped and gapless free fermion systems by mapping a ddimensional system in real space (gapped or gapless) to a gapped 2ddimensional quantum Hall system in phase space. This allows us to construct a phase space response theory for any free fermion system and to demonstrate that the generic topological feature of a gapless system is a quantized anomaly related to the edge anomaly of the phase space quantum Hall system.
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3781 2017 B  Inlibrary use 
 Mahajan, Raghu.
 2017.
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Weakly perturbing a system by an external force and measuring its response provides us with rich information about the underlying physics of the system. Linear response theory relates experimental quantities such as electrical conductivity and thermal conductivity to twopoint correlation functions of microscopic electric and heat current operators. There is a wealth of experimental data on conductivities. However, on the theoretical front, our knowledge away from the limit of small interparticle forces is poor. In this work, we present some new ideas and calculations that further our theoretical understanding of electric and heat transport when the interparticle forces are strong. In chapter 1, we set up our notation, define various twopoint correlation functions and derive the Kubo formula, paying special attention to subtleties that are often glossed over in many texts. In chapter 2, we derive an upper bound on diffusion that follows via an interplay of microscopic speed limits and local equilibration physics. In chapter 3, we analytically compute the electrical resistance in a special three dimensional system of gauge fields and matter. We are able to do the computation at arbitrary values of the coupling constant and frequency of the external driving electric field, albeit in the largeN limit. In chapter 4, we analyze the breakdown of the WiedemannFranz law at strong coupling and analyze various kinematic scenarios. We show that the Wiedemann Franz ratio should become extremely small if the momentum is approximately conserved (and there is no particlehole symmetry). In chapter 5, we use the memorymatrix formalism to compute the contribution of weak random fields to the transport near the Isingnematic quantum critical point. In chapter 6, we generalize our scope slightly to the general problem of computing timedependent quantities in quantum systems and present a new stateoftheart matrix product algorithm that allows us to numerically compute expectation values of observables at larger values of time than previously possible.
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Online 44. Xray studies of magnetism in the 3d transition metals [electronic resource] : from the nanoscale to the ultrafast to the nonlinear limit [2017]
 Chen, Zhao.
 2017.
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Resonant XRay phenomena associated with electronic coretovalence transitions have provided a wealth of information on modern magnetic nanostructures. In this thesis, we will describe two sets of experiments, both focusing on a different measurement related to the magnetic properties of the 3d transition metals, and both showcasing different advantages of modern XRay sources. We will show how large polarizationdependent resonant effects allow the determination of weak elementspecific static and transient magnetic moments and also offer the capability of recording movies of nanoscale magnetization dynamics with femtosecond temporal resolution. We demonstrate such effects with sensitive spectroscopic measurements of magnetism in Co/Cu alloys and of spin injection studies in Cu. In the next set of experiments, we show that when such techniques are extended to higher intensities at XRay free electron lasers, they also reveal completely new nonlinear effects, which are especially pronounced when probing spindependent effects. We will demonstrate how these nonlinear effects dramatically alter both magnetic diffraction and elastic transmission through a magneticallypatterned solid Co sample. Together, these studies show both the exceptional current capabilities of XRay in studies of 3d magnetism, but also the potential for studying interesting nonlinear phenomena in solids as brighter XRay sources become available in the future.
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Online 45. Argus [electronic resource] : a 16pixel millimeterwave spectrometer [2016]
 Sieth, Matthew Michael.
 2016.
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This thesis presents the development and deployment of Argus, a 16pixel millimeterwave spectrometer for the 100 m Robert C. Byrd Green Bank Telescope (GBT). Argus enables astronomical imaging at stateoftheart mapping speeds and high angular resolution over the 76116 GHz band. Its applications include studies of star formation, comets, astrobiology, and astrochemistry. Argus was installed on the GBT and measured rst light in March 2016. It will be available to the general radio astronomy community beginning in the winter 2016 observing semester. This work has demonstrated a novel scalable approach to building a focal plane array. The Argus array is built in 4pixel subunits, which are tiled together to form the 16pixel array. In principle, these subunits could be used as the building blocks of an even larger array. Every part is designed to be compact, massproducible, and as economical as possible. The core technology is based on miniaturized receiver modules, which integrate lownoise ampli ers, a bandpass lter, and a mixer into a single compact unit that would be amenable to automated assembly. The Argus receiver array achieved low noise performance over a very wide bandwidth, which both enables a number of new scienti c opportunities in the near term while demonstrating the viability of the design concept for future receiver designs.
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Online 46. Aspects of ChernSimonsmatter theories [electronic resource] [2016]
 Radic̆ević, Dorde.
 2016.
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This thesis studies several facets of ChernSimonsmatter theories, threedimensional systems of great interest to many physicists. The first of these three topics deals with theories in which matter is in the bifundamental representation of the ChernSimons gauge group, as these are the natural candidates for describing higherspin deviations from Einstein gravity. The second subject is the physics of theories with nonunitary matter, as these (in turn) are natural descriptions of fourdimensional Einstein gravity in de Sitter space. Finally, the third topic covered concerns the nature of monopoles in these theories, and includes a novel computation of scaling dimensions of simple monopole operators in conformal ChernSimonsfermion theories.
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Online 47. Aspects of strongly interacting quantum systems without translational symmetry [electronic resource] [2016]
 Ramirez, David M.
 2016.
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In this thesis, we study the emergence and dynamics of strongly interacting quantum field theories in a variety of spacetime dimensions, primarily using the holographic duality. We use the duality to probe the low energy dynamics, thermodynamics, and transport properties of such systems, with an emphasis on understanding the implications of translational symmetry breaking. After illustrating the emergence of strong dynamics in a concrete and phenomenologically motivated example, we utilize the duality to study the structure of low energy excitations in holographic systems, in particular finding instances where the low energy spectral weight has nontrivial momentum space structure. With the inclusion of translational symmetry breaking, we find explicit examples where conjectured bounds on the ratio shear viscosity to entropy density are parametrically violated, as well as evidence for new disordered strongly interacting quantum critical points with nontrivial, disorder dependent critical exponents and exotic transport behavior.
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Online 48. Ballistic conduction in graphene heterostructures [electronic resource] [2016]
 Lee, Menyoung.
 2016.
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Electronic transport in a solid is ballistic unless disturbed by disorder. This work describes experiments on a twodimensional electron system that resides in the heterostructure formed by graphene and hexagonal boron nitride. The ballistic conduction of electrons is probed across micron length scales by examining the transverse electron focusing effect, in which semiclassical electron trajectories emanating from a point on the system boundary are bent by an applied magnetic field and are focused onto another point. Internal reflection at the boundary extends these trajectories into skipping orbits; the observation and analysis of ballistic conduction that proceeds thus characterizes the interaction of an electron in graphene with the edge. Transverse electron focusing is also exhibited in the 14 nmperiod moire superlattice, which is formed by the incommensurability and misalignment between the graphene and boron nitride lattices. At low temperatures, ballistic motion exhibits caustics of skipping orbits extending over hundreds of superlattice periods, reversals of the cyclotron revolution for five successive minibands, and breakdown of cyclotron orbits near van Hove singularities. A theory of nearly free Dirac fermions that obey semiclassical equations of motion successfully describes the system. The interlayer interaction parameter and the full miniband structure can be determined quantitatively. Probing such miniband conduction properties is a necessity for engineering novel transport behaviors in superlattices, and the results suggest possibilities for new device functions and more exotic physics in similar van der Waals heterostructures. A direct pointtopoint measurement of ballistic transport also enables quantitative measurement of the effect of the electronelectron interaction on the transport of quasiparticles in a clean twodimensional Fermi liquid, in particular the crossover from the regime of ballistic transport to the viscous and hydrodynamic flow regime as a function of increasing temperature.
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Online 49. Coherent LQG control, freecarrier oscillations, optical ising machines and pulsed OPO dynamics [electronic resource] [2016]
 Hamerly, Ryan Michael.
 2016.
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Broadly speaking, this thesis is about nonlinear optics, quantum mechanics, and computing. More specifically, it covers four topics: Coherent LQG Control, FreeCarrier Oscillations, Optical Ising Machines and Pulsed OPO Dynamics. Tying them all together is a theory of open quantum systems called the SLH model, which I introduce in Chapters 12. The SLH model is a general framework for open quantum systems that interact through bosonic fields, and is the basis for the quantum circuit theory developed in the text. Coherent LQG control is discussed in Chapters 34, where I demonstrate that coherent feedback outperforms measurementbased feedback for certain linear quadraticGaussian (LQG) problems, and explain the discrepancy by the former's simultaneous utilization of both light quadratures. Semiclassical truncatedWigner techniques for quantumoptical networks are discussed in Chapter 5, leading to a thorough discussion of quantum noise in systems with freecarrier nonlinearities (Chapter 6), comparison to the Kerr nonlinearity, and potential applications for analog computing based on limit cycles and amplification (Chapters 78). Ising machines based on optical parametric oscillators (OPOs) are discussed in Chapters 910, the former focusing on large 1D and 2D networks of OPOs, and the latter on the dynamics of a single OPO in the ultrafast, synchronouslypumped regime. Optical properties and design considerations for silicon photonic waveguides are are treated in Chapter 11.
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Online 50. Datadriven methods for modeling of extreme events [electronic resource] [2016]
 Shenoy, Saahil.
 2016.
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The motivation of this thesis is to model the risk of extreme events. With rapidly increasing amounts of available data, the statistics on extreme events is more accurate. The developed methodology in this thesis work extends existing actuarial science and financial risk approaches. These approaches use a branch of statistics known as extreme value theory (EVT). One of the extensions is analyzing risk trends across years for each calendar month. This is a highly nontrivial problem because extreme events might not happen every year for a given month. A Bayesian maximum a posteriori (MAP) formulation is applied to tackle this problem. One of the main applications of this novel method is characterizing the risk trends of 100 year extreme high temperature events. We focus on these extreme weather events since their occurrences are immensely disruptive and damaging. The nontriviality of the problem is in distinguishing climate change from the immense variations in weather, both spatially and temporally. The data analyzed is from the continental U.S. from 1979 to 2015. We show that aggregation from multiple locations is valid in order to get more accurate statistics on 100 year extremes. There is a factor of 2.7 relative increase for 100year extreme high temperature event risk that is found in the last 4 decades of the climate data. This is primarily caused by both a factor 2.3 relative increase in the number of and a 41\% increase in magnitude of extreme high temperature events over the last 37 years. Another method is also developed for building a nonparametric stochastic model of the distribution from large data sets. This is done with an modified version of quantile regression (QR). This new QR formulation also tackles two major issues with the original QR method itself. In the second main application example, we consider probabilistic forecasting of the loads in electrical power grid. A probabilistic forecast is given by our estimated QR model. The probabilistic evaluation of risk is important because load volatility is increasing with the ongoing proliferation of the renewable generation. The most important risk factor is that the required amount of the electricity cannot be procured at the spot market, because the standby generation capacity is insufficient. An application to electric utility data shows significant improvement in load balancing risk compared to existing methods.
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Online 51. Demonstration of the hollow channel plasma wakefield accelerator [electronic resource] [2016]
 Gessner, Spencer J.
 2016.
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A plasma wakefield accelerator is a device that converts the energy of a relativistic particle beam into a largeamplitude wave in a plasma. The plasma wave, or wakefield, supports an enormous electric field that is used to accelerate a trailing particle beam. The plasma wakefield accelerator can therefore be used as a transformer, transferring energy from a highcharge, lowenergy particle beam into a highenergy, lowcharge particle beam. This technique may lead to a new generation of ultracompact, highenergy particle accelerators. The past decade has seen enormous progress in the field of plasma wakefield acceleration with experimental demonstrations of the acceleration of electron beams by several gigaelectronvolts. The acceleration of positron beams in plasma is more challenging, but also necessary for the creation of a highenergy electronpositron collider. Part of the challenge is that the plasma responds asymmetrically to electrons and positrons, leading to increased disruption of the positron beam. One solution to this problem, first proposed over twenty years ago, is to use a hollow channel plasma which symmetrizes the response of the plasma to beams of positive and negative charge, making it possible to accelerate positrons in plasma without disruption. In this thesis, we describe the theory relevant to our experiment and derive new results when needed. We discuss the development and implementation of special optical devices used to create long plasma channels. We demonstrate for the first time the generation of meterscale plasma channels and the acceleration of positron beams therein.
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Online 52. Discovering the QCD axion with black holes and gravitational waves [electronic resource] [2016]
 Huang, Xinlu.
 2016.
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Advanced LIGO is the first experiment to detect gravitational waves. Through su perradiance of stellar black holes, it may also be the first experiment to discover the QCD axion with decay constant above the GUT scale. When an axion's Comp ton wavelength is comparable to the size of a black hole, the axion binds to the black hole, forming a "gravitational atom." Through the superradiance process, the number of axions occupying the bound levels grows exponentially, extracting energy and angular momentum from the black hole. Axions transitioning between levels of the gravitational atom and axions annihilating to gravitons can produce observable gravitational wave signals. The signals are longlasting, monochromatic, and can be distinguished from ordinary astrophysical sources. We estimate up to O(1) transition events at aLIGO for an axion between 10^−11 and 10^−10 eV and up to 10^4 annihila tion events for an axion between 10^−13 and 10^−11 eV. In the event of a null search, aLIGO can constrain the axion mass for a range of rapidly spinning black hole formation rates. Axion annihilations are also promising for much lighter masses at future lowerfrequency gravitational wave observatories; the rates have large uncertainties, dominated by supermassive black hole spin distributions. Our projections for aLIGO are robust against perturbations from the black hole environment and account for our updated exclusion on the QCD axion of 6 × 10^−13 eV < μa < 2 × 10^−11 eV suggested by stellar black hole spin measurements.
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Online 53. An effective field theory approach to cosmological structure formation [electronic resource] [2016]
 Foreman, Simon.
 2016.
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One of the main frontiers of observational cosmology is to map out how matter is distributed throughout the universe. The clustering patterns of galaxies and other astrophysical objects contain imprints of the universe's expansion history, the properties of the quantum fluctuations that are believed to have seeded the latetime structures we observe, and possibly other new and exotic physical processes. To extract this information from observations, we require a robust theoretical framework for how gravitational clustering works at large distances. This dissertation presents such a framework, which adapts the ideas of "effective field theory" (originally developed in the context of particle physics and quantum fields) to describe how small perturbations in an initially homogeneous distribution of matter evolve through cosmic time. In this framework, the perturbations are described as an effective fluid at long distances, with a stress tensor that parametrizes the effects of shortwavelength processes on the longdistance dynamics of the fluid. This stress tensor can be written as an expansion in longwavelength fields (such as the matter overdensity) and spatial derivatives, and the coefficients of this expansion can be matched either to observations or to numerical simulations of gravitational clustering. Through several explicit calculations of correlation functions (particularly the power spectrum) of the cosmic density field, I demonstrate how the presence of this stress tensor renders the theory free of many of the issues that have plagued other perturbative approaches to gravitational clustering. I also perform several comparisons of the theory's predictions to measurements from dark matteronly Nbody simulations, demonstrating the theory's ability to reproduce these measurements at over a wider range of scales and at higher precision than previously possible. The results in this dissertation represent significant advances in our understanding of cosmological perturbation theory, and their eventual application to observations of largescale structure will likely be a great help in furthering our knowledge about the universe we inhabit.
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Online 54. The effective field theory of largescale structure in cosmology [electronic resource] [2016]
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So far, the cosmic microwave background has provided most of the significant constraints on cosmological parameters, but because of Silk damping and foreground contamination, the Planck Satellite has essentially reached the limit in constraining nonGaussianity in scalar modes with the cosmic microwave background. Fortunately, the distribution of galaxies today is correlated with the conditions present in the early universe, so largescale structure surveys can help us understand the early universe by observing the currentday galaxy distribution. In this way, it is likely that the next leading source of cosmological information will come from largescale structure surveys like LSST and Euclid. In order for largescale structure to significantly improve our knowledge of the early universe, for example by constraining f_NL < 1 through bispectrum measurements, the largescale structure observables must be understood to percent level, even in the quasilinear regime of structure formation. Recently, a research program called the Effective Field Theory of LargeScale Structure was launched with this purpose. In this thesis, I will develop two pieces of that program: the effective field theory in redshift space, and the description of baryonic effects in the effective field theory. Finally, I will present work which computes the first slowroll corrections to the volume of the universe and the universal entropy bound for slowroll eternal inflation.
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Online 55. Electrical, mechanical, and optical characterization of twodimensional materials with molecular overlayers [electronic resource] [2016]
 Gallagher, Patrick.
 2016.
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A twodimensional object is entirely surface, with no interior. Its immediate surroundings will accordingly influence its response to electrical, mechanical, and optical stimuli. This thesis explores two different twodimensional electron systems with molecular overlayers: the surface electron liquid in strontium titanate induced by electrolyte gating, and graphene decorated by ordered adsorbates. Strontium titanate is a band insulator that goes superconducting when doped with remarkably few electrons. By accumulating positive ions at a strontium titanate surface, the electrolyte gating technique can create a twodimensional electron system with gatetunable superconductivity. I combine an electrolyte gate with nanopatterned metaloxide gates to realize the first gatetunable superconducting weak link in this promising correlated electron system. With the same technique I create a ballistic onedimensional channel in strontium titanate, and use this channel to perform inplane tunneling spectroscopy of the superconducting state. Finally, using strontium titanate as a test case, I describe a method to improve mobility of generic electrolytegated surface systems by protecting the channel with a thin layer of hexagonal boron nitride. In the second part of this thesis, I use highresolution atomic force microscopy to reveal a nanotexture that unexpectedly forms on flakes of graphene (and boron nitride) prepared in laboratory air: a "superlattice" of topographic stripes whose period is 4 nm. I argue that these stripes are selfassembled environmental adsorbates, and show that they are responsible for graphene's strongly anisotropic frictiona property previously believed to result from periodic rippling of the graphene sheet itself. In agreement with this selfassembly picture, I demonstrate that the local axis of high friction can be patterned with submicron precision by appropriate mechanical contact. I further show that the stripes produce anisotropic optical response, and I discuss the potential influence of the stripesuperlattice on graphene's electronic properties.
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3781 2016 G  Inlibrary use 
 Yuan, Hongyuan.
 2016.
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Thermionic energy converters (TECs) are a direct heattoelectricity conversion technology with the potential to outperform the current stateoftheart solidstate energy conversion technologies in a wide range of working temperatures. TECs could not only be applied to largescale power plants in a tandem cycle, but could also be deployed in distributed power generation systems at small scales. In a TEC, electrons evaporate from a hot electrode (the cathode) into a vacuum gap and are collected by a cooler electrode (the anode) to generate electric energy. However, the published TECs suffer from low output voltage as well as low output current because the work function of the anode is too high and the space charge barrier in the interelectrode is too strong, which ultimately lead to low conversion efficiency. In this thesis, I will first present a phenomenological model to calculate a material's work function. This model shows that graphene has great potential to yield an ultralow work function. I will then experimentally demonstrate such a graphene anode in an ultrahigh vacuum system. The graphene is grown on a piece of copper foil by chemical vapor deposition. It is then transferred onto a 20 nm thick HfO2 layer prepared by atomic layer deposition on silicon. After insitu deposition of a monolayer of Cs/O, the work function of the graphene anode is dramatically reduced from 4.62 eV to 1.25 eV. Furthermore, I will show that electrostatic gating graphene through the HfO¬2 dielectric layer can further reduce the work function of graphene. Due to the absence of surface Fermi level pinning and low surface state density according to graphene's linear dispersion relation, the Fermi level of graphene can by effectively raised through a DC bias with negligible energy consumption. I will show that combining Cs/O surface coating and electrostatic gating would lead to a worldrecord low work function for graphene of 1.0 eV. Finally, I will demonstrate a TEC prototype based on this graphene anode, together with a commercial dispenser cathode. At the cathode working temperature of 1000 ˚C, the work functions of both of the electrodes are reduced by Ba. In addition, this TEC prototype deploys a nanomanipulator system that can reduce the interelectrode gap to 17 μm, leading to a much reduced space charge barrier. By addressing the two challenges simultaneously, a low work function anode and minimizing the space charge barrier, the overall conversion efficiency of this TEC prototype is improved by a factor of over 50, with an estimated maximum electronic conversion efficiency of 9.8 %, which is the highest reported by far at this relatively low working temperature.
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Online 57. Globalmode helioseismology [electronic resource] : extensions of a wellused method [2016]
 Larson, Tim.
 2016.
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Globalmode helioseismology has been used extensively to precisely infer the detailed properties of the solar interior. Multiple algorithms have been applied to several different datasets, which now span over two solar cycles. This dissertation deals primarily with two instruments, namely the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory, and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory. For MDI, we have two velocity datasets spanning the 15 years from 1996 to 2011: highresolution images which were taken for a few months each year, and lowresolution images which were taken almost all the time. For HMI, we have even higher resolution velocity images taken since 2010. Unlike MDI, HMI also provides intensity data. The initial motivation for this study was to address known systematic errors in the analysis of MDI data, as well as discrepancies with inferences drawn by other projects, most notably the Global Oscillation Network Group. In particular, the MDI results indicated a highlatitude peak in the solar rotation rate, which is now believed to be spurious. Also, certain fits resulted in normalized residuals that indicate the fit is not using the correct model. Lastly, MDI saw an annual periodicity in frequency shifts, which can only be because of errors in geometry. Now that MDI is no longer operating, it has also become important to achieve continuity between the MDI and HMI datasets. To that end, both have been processed in their entirety using the same set of software. Since the original software was written when computational capabilities were far less than now, this involved the application of several updates. At the same time, we have adopted better models of the physics behind the oscillations and applied various geometric corrections. In this dissertation we investigate how these changes affected the globalmode parameters from the MDI analysis and the systematic errors therein. We then apply the fully updated analysis to the HMI data, and make a comparison of mode parameters derived from the various datasets from the two instruments. We find methods that decrease or eliminate the systematic errors mentioned above. Hence, inferences of the Sun's interior rotation have become more robust. Further, the comparison between MDI and HMI encourages the concatenation of their datasets, which may allow for the detection of new oscillation modes.
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Online 58. Imaging current in materials [electronic resource] [2016]
 Spanton, Eric M.
 2016.
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Scanning superconducting quantum interference device (SQUID) microscopy is an incredibly sensitive way to image magnetic fields. One application of this technique is to spatially map magnetic fields which originate from moving electrons (i.e. electrical current), and interpret the pattern of current in order to learn more about how electrons behave in interesting materials. In lanthanum aluminatestrontium titanate, two insulators which can host a twodimensional conducting state at their interface, we discovered locally enhanced conduction due to domain structure in the strontium titanate. 2D topological insulators are a class of materials which are predicted to host special conducting states along the edges of patterned devices, and we were able to image current along the edges of devices in two such materials: HgTe quantum wells and InAs/GaSb quantum wells. In InAs/GaSb, we found that backscattering in the edges was temperature independent and elucidated the presence of edge states in socalled 'trivial' regimes. These results call into question the prevailing interpretation of edge states in InAs/GaSb as topological, and conclude that better experimental evidence is required to definitively identify a 2D topologically insulating state in this material. Finally, we've investigated a fundamental property of Josephson junctions called the currentphase relation in fewmode InAs nanowire junctions. InAs nanowires which are in close contact with conventional superconductors are of great interest due to the possible realization of exotic particles called Majorana quasiparicles which may be of use for quantum computation. We've probed the disorder associated with adding superconductivity to nanowires by measuring the shape of the currentphase relation and finding that it fluctuates as a function of electron density and from junction to junction.
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Online 59. Investigating the quantum properties of jets and the search for a supersymmetric top quark partner with the ATLAS detector [electronic resource] [2016]
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Quarks and gluons are the fundamental building blocks of matter responsible for most of the visible energy density in the universe. However, they cannot be directly observed due to the confining nature of the strong force. The Large Hadron Collider (LHC) uses protonproton collisions to probe the highest energy reactions involving quarks and gluons happening at the smallest distance scales ever studied in a terrestrial laboratory. The observable consequence of quark and gluon production in these reactions is the emergent phenomenon known as the jet: a collimated stream of particles traveling at nearly the speed of light. The quantum properties of the initiating quarks and gluons are encoded in the distribution of energy inside and around jets. These quantum properties of jets can be used to study the high energy nature of the strong force and provide a way to tag the hadronic decays of heavy boosted particles. The ATLAS detector at the LHC is wellsuited to perform measurements of the internal structure of high energy jets. A variety of novel techniques utilizing the unique capabilities of the ATLAS calorimeter and tracking detectors are introduced in order to probe the experimental and theoretical limits of the quantum properties of jets. Studying quarks and gluons may also be the key to understanding the fundamental problems with the Standard Model (SM) of particle physics. In particular, the top quark has a unique relationship with the newly discovered Higgs boson and as such could be a portal to discovering new particles and new forces. In many extensions of the SM, the top quark has a partner with similar relationships to other SM particles. For example, a scalar top partner (stop) in Supersymmetry (SUSY) could solve the Higgs boson mass hierarchy problem. Miraculously, a SUSY neutralino could also account for the dark matter observed in the universe and may be copiously produced in stop decays. Highenergy top quarks from stop decays result in jets with a rich structure that can be identified using the techniques developed in the study of the quantum properties of jets. While there is no significant evidence for stop production at the LHC, the stringent limits established by this search have important implications for SUSY and other models.
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Online 60. Modeling the distribution of dark matter and its connection to galaxies [electronic resource] [2016]
 Mao, YaoYuan.
 2016.
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Despite the mysterious nature of dark matter and dark energy, the LambdaCold Dark Matter (LCDM) model provides a reasonably accurate description of the evolution of the cosmos and the distribution of galaxies. Today, we are set to tackle more specific and quantitative questions about the galaxy formation physics, the nature of dark matter, and the connection between the dark and the visible components. The answers to these questions are however elusive, because dark matter is not directly observable, and various unknowns lie between what we can observe and what we can calculate. Hence, mathematical models that bridge the observable and the calculable are essential for the study of modern cosmology. The aim of my thesis work is to improve existing models and also to construct new models for various aspects of the dark matter distribution, as dark matter structures the cosmic web and forms the nests of visible galaxies. Utilizing a series of cosmological dark matter simulations which span a wide dynamical range and a statistical sample of zoomin simulations which focus on individual dark matter halos, we develop models for the spatial and velocity distribution of dark matter particles, the abundance of dark substructures, and the empirical connection between dark matter and galaxies. As more precise observational results become available, more accurate models are then required to test the consistency between these results and the LCDM predictions. For all the models we investigate, we find that the formation history of dark matter halos always plays a crucial role. Neglecting the halo formation history would result in systematic biases when we interpret various observational results, including dark matter direct detection experiments, the detection of dark substructures with stronglensed systems, the largescale spatial clustering of galaxies, and the abundance of dwarf galaxies. Rectifying this, our work will enable us to fully utilize the complementary power of diverse observational datasets to test the LCDM model and to seek new physics.
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