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ItemDensity-Induced Spin-Nematic Squeezing in a Spin-1 Bose-Einstein Condensate(Georgia Institute of Technology, 2024-04-28) Barrios, MaryroseDensity or pressure modulation of materials is an important method for tuning and engineering interactions within materials studied in condensed matter systems. This tuning is often used to alter or modify the underlying properties of the material, leading to the crossing of a phase transition or enhanced chemical or mechanical properties. This thesis investigates the possibility of whether a similar approach might be employed in the study of ultracold atoms present within a spinor condensate. In our system we use the confining trap potential to modulate and increase the density of the system in such a way as to push the cloud of atoms from non-interacting to interacting, and across a quantum critical point. By crossing over into this new phase, we are able to perform a constant magnetic field quench to observe both spin mixing and spin-nematic squeezing. This allows us to achieve -8.4 ± 0.8 dB of squeezing and shows promise for future density-driven interactions.
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ItemUnraveling the Knot-so-Simple Behavior of Knitted Fabrics(Georgia Institute of Technology, 2024-04-27) Singal, KrishmaKnitted fabrics are a ubiquitous part of our day-to-day lives. Although we primarily interact with it through clothing, the programmable nature of knitted fabrics lends to its potential in a myriad of fields. Knitting is made by manipulating yarn, which is often inelastic, into a lattice of slipknots with emergent elastic properties. How the yarn is manipulated throughout the fabric, what stitches it forms and how they’re patterned, impacts the resultant fabric behavior under mechanical deformation. Traditionally, this elastic response of knitted fabrics is qualitatively determined, but this study works to systematically understand and quantify the programmable nature of knitted materials. We find that small scale changes in the topology of the yarn between stitches, the boundaries between stitches, have large scale impacts on the bulk fabric response. Not only on the stitch level, but the lengthscale of these boundaries further influences the fabric behavior. We probe the multi-scale behavior and application of knitting through several experimental studies: varying constituent yarn type composing the fabrics, comparing behaviors of classic periodic knitting patterns, exploring the impact of aperiodic patterned fabrics, and testing applications of knitting in biomimicry and biomechanics via known pattern composites.
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ItemDynamics and Transport in Strongly Correlated Quantum Magnets(Georgia Institute of Technology, 2024-04-24) Hakani, SamiThis dissertation discusses Raman dynamics and chiral orbital currents in strongly correlated quantum magnets. Such spin systems can host exotic quantum liquid phenomena including fractional excitations, emergent gauge fields, and novel particle statistics. In addition to broadening basic scientific knowledge, understanding the dynamics and transport of these magnetic systems can further technological applications in quantum computing and electronics. This is demonstrated by probing quantum liquid phenomena using Raman scattering on the spin-1/2 quantum liquid candidate Ba4Ir3O10. In a collaborative study, Raman scattering provides three signatures for fractional spinon excitations: (1) a broad spectral hump consistent with a continuum arising from 4-body scattering of Luttinger spinons, (2) strong phonon damping due to spin-phonon coupling due to spin-orbit interactions, and (3) the absence of (1) and (2) and the precipitation of magnetic order due to a 2% non-magnetic chemical substitution. Transport phenomena is studied in ferrimagnetic Mn3Si2Te6 which demonstrates colossal magnetoresistance in absence of magnetic polarization. In a second collaborative study, a crystallographic symmetry analysis demonstrates chiral orbital current patterns are consistent with experimental transport measurements. The demonstrated control of chiral orbital current enabled colossal magnetoresistance provides potential utility for future quantum technological applications. Finally, a novel effect in Raman dynamics is explored in the presence of crystalline topological defects. Even when such defects do not couple to the low energy Hamiltonian, it is shown that they can produce qualitatively new effects by coupling to electric field probes. Such effects rely on an underlying spinon liquid state, and they are not observed for magnetically ordered or gapped phases. Potential applications include using crystalline topological defects to modify response-theory operators independently of the Hamiltonian and thereby generate new probes of quantum phases.
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ItemModeling Ganymede's Interaction with the Jovian Magnetosphere: Ionospheric Outflow and the Juno PJ34 Flyby(Georgia Institute of Technology, 2024-04-04) Stahl, Aaron M.Using a hybrid model (kinetic ions, fluid electrons), we provide a three-dimensional model of Ganymede’s interaction with the Jovian magnetosphere and the moon’s ionospheric outflow. We also provide context for plasma and magnetic field observations from Juno's PJ34 flyby of Ganymede on 07 June 2021. Using five model configurations that successively increase the complexity of Ganymede’s atmosphere and ionosphere through the inclusion of additional particle species and ionization mechanisms, we examine the density and flow patterns of pick-up ions with small (H2+), intermediate (H2O+), and large (O2+) masses in Ganymede’s interaction region. The results are validated by comparing the modeled magnetic field and ion densities against time series from Juno’s magnetometer and plasma instruments. The major findings are: (a) Ganymede’s internal dipole dominated the magnetic field signature observed inside the moon’s magnetosphere, while plasma currents shaped the field perturbations within the “wake” region detected along the Jupiter-averted magnetopause. (b) Ganymede’s pick-up tail leaves a subtle, but clearly discernible imprint in the magnetic field downstream of the moon. (c) Heavy pick-up ions dominate ionospheric outflow and form a tail with steep outer boundaries. (d) During the Juno flyby, the position of Ganymede’s Jupiter-facing magnetopause varied in time due to Kelvin-Helmholtz waves traveling along the boundary layer. As such, the location of the Jupiter-facing magnetopause observed by Juno represents only a single snapshot of this time-dependent process. (e) Ionospheric hydrogen ions are partially generated outside of Ganymede’s magnetopause, forming a dilute H2+ corona that surrounds the moon’s magnetosphere. (f) Most H2O+ ions are produced at low latitudes where field lines are closed, resulting in a very dilute pick-up tail for this species.
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ItemProgramming Mechanics in Knitted Materials, Stitch by Stitch Data Repository(Georgia Institute of Technology, 2024-02) Singal, Krishma ; Dimitriyev, Michael S. ; Gonzalez, Sarah E. ; Cachine, Alexander P. ; Quinn, Sam ; Matsumoto, Elisabetta A.
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ItemExact coherent structures and non-universality in the direct cascade in two-dimensional turbulence(Georgia Institute of Technology, 2024-01-10) Zhigunov, DmitriyTurbulence is the most important problem in physics and applied mathematics, with applications ranging from astrophysics, to engineering, to plumbing, and more. Turbulent flows are often characterized by the presence of various cascades, which transport various quantities across length scales. This dissertation focuses on turbulence confined in two-dimensions, which has two cascades: an inverse (energy) cascade that moves energy towards increasingly larger scales, and a direct (enstrophy) cascade that moves the enstrophy towards smaller scales. The energy cascade leads to the formation of large-scale vortices, which often take up the largest length allowed by the domain. The first part of this dissertation flows focuses on the dynamics of these large scale vortices, where we find that these vortices behave for substantial time intervals like specific solutions of the Euler equation. These solutions are in many ways analogous to recurrent solutions of the Navier-Stokes equation which are often referred to as exact coherent structures. On the other hand, these solutions have a number of properties which distinguish them from their Navier-Stokes counterparts, such as the fact that they exist in continuous, multiparameter families. At the same time, the classical theory of the direct cascade by Kraichnan, Leith, and Batchelor fails to predict the proper scaling of the enstrophy spectrum found in numerical simulations and experiments. This discrepancy is often attributed to the presence of large-coherent vortices. We will provide a physically interpretable mechanism for the direct cascade that recovers KLB predictions in the absence of large-scale vortices, but leads to deviations in their presence. Finally, we return directly to the large-scale dynamics we explain in the first section, and investigate exactly how properties of the large-scale flow affect the scaling of the enstrophy spectrum.
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ItemData for the publication "Pressure control of magnetic order and excitations in the pyrochlore antiferromagnet MgCr2O4"(Georgia Institute of Technology, 2024-01) Mourigal, MartinMgCr2O4 is one of the best-known realizations of the pyrochlore-lattice Heisenberg antiferromagnet. The strong antiferromagnetic exchange interactions are perturbed by small further-neighbor exchanges such that this compound may in principle realize a spiral spin liquid (SSL) phase in the zero-temperature limit. However, a spin Jahn-Teller transition below TN≈13 K yields a complicated long-range magnetic order with multiple coexisting propagation vectors. We present neutron scattering and thermo-magnetic measurements of MgCr2O4 samples under applied hydrostatic pressure up to P=1.7 GPa demonstrating the existence of multiple close-lying nearly degenerate magnetic ground states. We show that the application of hydrostatic pressure increases the ordering temperature by around 0.8 K per GPa and increases the bandwidth of the magnetic excitations by around 0.5 meV per GPa. We also evidence a strong tendency for the preferential occupation of a subset of magnetic domains under pressure. In particular, we show that the k=(0,0,1) magnetic phase, which is almost negligible at ambient pressure, dramatically increases in spectral weight under pressure. This modifies the spectrum of magnetic excitations, which we interpret unambiguously as spin waves from multiple magnetic domains. Moreover, we report that the application of pressure reveals a feature in the magnetic susceptibility above the magnetostructural transition. We interpret this as the onset of a short-range ordered phase associated with k=(0,0,1), previously not observed in magnetometry measurements.
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ItemRaw data and simulation code for "Quantum-to-classical crossover in generalized spin systems – the temperature-dependent spin dynamics of FeI2"(Georgia Institute of Technology, 2024-01) Mourigal, MartinSimulating quantum spin systems at finite temperatures is an open challenge in many-body physics. This work studies the temperature-dependent spin dynamics of a pivotal compound, FeI2, to determine if universal quantum effects can be accounted for by a phenomenological renormalization of the dynamical spin structure factor S(q,ω) measured by inelastic neutron scattering. Renormalization schemes based on the quantum-to-classical correspondence principle are commonly applied at low temperatures to the harmonic oscillators describing normal modes. However, it is not clear how to extend this renormalization to arbitrarily high temperatures. Here we introduce a temperature-dependent normalization of the classical moments, whose magnitude is determined by imposing the quantum sum rule, i.e. ∫dωdqS(q,ω)=NSS(S+1) for NS dipolar magnetic moments. We show that this simple renormalization scheme significantly improves the agreement between the calculated and measured S(q,ω) for FeI2 at all temperatures. Due to the coupled dynamics of dipolar and quadrupolar moments in that material, this renormalization procedure is extended to classical theories based on SU(3) coherent states, and by extension, to any SU(N) coherent state representation of local multipolar moments.
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ItemData for the publication "Cryogenic platform to investigate strong microwave cavity-spin coupling in correlated magnetic materials"(Georgia Institute of Technology, 2024) Jones, Aulden ; Lilly, Michael ; Mounce, Andrew ; Mourigal, MartinWe present a comprehensive exploration of loop-gap resonators (LGRs) for electron spin resonance (ESR) studies, enabling investigations into the hybridization of solid-state magnetic materials with microwave polariton modes. The experimental setup, implemented in a Physical Property Measurement System by Quantum Design, allows for measurements of ESR spectra at temperatures as low as 2 Kelvin. The versatility of continuous wave ESR spectroscopy is demonstrated through experiments on CuSO4·5H2O and MgCr2O4, showcasing the g-tensor and magnetic susceptibilities of these materials. The study delves into the challenges of fitting spectra under strong hybridization conditions and underscores the significance of proper calibration and stabilization. The detailed guide provided serves as a valuable resource for laboratories interested in exploring hybrid quantum systems through microwave resonators.
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ItemExperimental Data for "Spatial constraints and stochastic seeding subvert microbial arms race"(Georgia Institute of Technology, 2024-01) Copeland, Raymond ; Zhang, Christopher ; Hammer, Brian K. ; Yunker, Peter J.Surface attached communities of microbes grow in a wide variety of environments. Often, the size of these microbial community is constrained by their physical surroundings. However, little is known about how size constraints of a colony impact the outcome of microbial competitions. Here, we use individual-based models to simulate contact killing between two bacterial strains with different killing rates in a wide range of community sizes. We found that community size has a substantial impact on outcomes; in fact, in some competitions the identity of the most fit strain differs in large and small environments. Specifically, when at a numerical disadvantage, the strain with the slow killing rate is more successful in smaller environments than in large environments. The improved performance in small spaces comes from finite size effects; stochastic fluctuations in the initial relative abundance of each strain in small environments lead to dramatically different outcomes. However, when the slow killing strain has a numerical advantage, it performs better in large spaces than in small spaces, where stochastic fluctuations now aid the fast killing strain in small communities. Finally, we experimentally validate these results by confining contact killing strains of Vibrio cholerae in transmission electron microscopy grids. The outcomes of these experiments are consistent with our simulations. When rare, the slow killing strain does better in small environments; when common, the slow killing strain does better in large environments. Together, this work demonstrates that finite size effects can substantially modify antagonistic competitions, suggesting that colony size may, at least in part, subvert the microbial arms race.