Condensed Matter Physics Commons^™

Curvature In Compressed Thin Cylindrical Shells Approaching The Isometric Limit, Nicole Voce

Senior Honors Projects, 2020-current

The ability to manipulate surface elastic instabilities finds many applications in engineering smart interfaces, e.g. in fluid-structure interaction and micro-fabrication. We study the buckling of a thin cylindrical shell constrained to slide onto an inner non-deformable pipe. Our goal is to characterize the relationship between the shell thickness and the localization of stresses by using curvature measurements. First, we induce surface buckling by immobilizing one end of the shell and applying force to the other end. Then, we obtain a virtual reconstruction of the surface from 3D optical scanning and compute the Gaussian curvature for every point on the mesh. …

Skyrmion Fluctuations At A First-Order Phase Transition Boundary, V. Esposito, X. Y. Zheng, M. H. Seaberg, S. A. Montoya, B. Holladay, A. H. Reid, R. Streubel, J. C.T. Lee, L. Shen, J. D. Koralek, G. Coslovich, P. Walter, S. Zohar, V. Thampy, M. F. Lin, P. Hart, K. Nakahara, P. Fischer, W. Colocho, A. Lutman, F. J. Decker, S. K. Sinha, E. E. Fullerton, S. D. Kevan, S. Roy, M. Dunne, J. J. Turner

Robert Streubel Papers

Magnetic skyrmions are topologically protected spin textures with promising prospects for applications in data storage. They can form a lattice state due to competing magnetic interactions and are commonly found in a small region of the temperature - magnetic field phase diagram. Recent work has demonstrated that these magnetic quasi-particles fluctuate at the μeV energy scale. Here, we use a coherent x-ray correlation method at an x-ray free-electron laser to investigate these fluctuations in a magnetic phase coexistence region near a first-order transition boundary where fluctuations are not expected to play a major role. Surprisingly, we find that the relaxation …

Investigation Of Mnxni1-Xo Thin Films Using Pulsed Laser Deposition, Md Ashif Anwar

Graduate Theses/Dissertations

The exchange bias (EB) effect, especially in nanomaterials, is highly promising for use in antiferromagnet-based spintronics applications. NiO is a well known antiferromagnetic material with a high Néel temperature (525K) and can exhibit ferromagnetism/ ferrimagnetism by adding other magnetic transition elements. Our previous work has shown that the antiferromagnetic characteristics of conventional NiO insulating nanostructured material can be altered to have substantial ferrimagnetic characteristics by doping NiO with Mn or Co. Pulsed laser deposition (PLD) was used to grow heterostructures comprised of a nanostructured thin NiO film deposited on the surface of a MgO (100) and Al₂O_{3 …}

Development Of Co2 Laser-Heating For The Study Of Wide Band Gap Oxide Materials, Christian Matthew Childs

UNLV Theses, Dissertations, Professional Papers, and Capstones

The ability to access a vast region of the pressure-temperature landscape using energy density tuning enables exotic states of matter to be probed. A well documented method for such exploration, under static conditions, is the use of the laser-heated diamond anvil cell (LH-DAC), accessing a combination of high pressure (>300 GPa) and high temperature (>5000 K). This thesis presents our development of direct CO2 laser heating techniques to study a series of wide band gap insulators, La2Sn2O7, ZrO2, and CeO2, under high pressure conditions. The lasing frequency of CO2 lasers is such that these wide band gap materials …

Symmetry And Interface Considerations For Interactions On Mos2, Prescott E. Evans

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

The critical role of symmetry, in adsorbate-MoS₂ interactions, has been demonstrated through a variety of electronic structure, topology, and catalytic studies of MoS₂ and MoS₂ composites.A combination of density functional theory and experiment exhibiting diiodobenzene isomer dependent adsorption rates highlight frontier orbital symmetry as key to adsorption on MoS₂. It is clear that the geometry and symmetry of MoS₂ influences the creation and stability of surface defects, that in turn affect catalytic activity and a myriad of other applications. We have shown that surface reactions such the methanol to methoxy reaction can create defects …

Investigations Of Technetium Metal And The Synthesis Of Binary Technetium Nitrides Under Extreme Conditions, Emily Siska

UNLV Theses, Dissertations, Professional Papers, and Capstones

Technetium (Tc) is the lightest of the radioactive elements and has no stable isotopes. Significant quantities of Tc are not naturally occurring on earth. However, technetium is found in high fission yield in nuclear reactors and produced for medical imaging. With its long half life, and high mobility in the environment make it of particular interest. To that end, the fundamental chemistry of Tc and Tc compounds is not as well understood compared to neighboring elements on the periodic table. Therefore, fundamental studies designed to better understand this transition metal, coupled with more targeted investigation at high temperature and pressure …

An Analysis Of The Debate Over Creation, Evolution, And The Timeline Of The Universe At An Ecumenical Christian University, Mason Pohlman

Honors Scholars Collaborative Projects

Throughout a significant portion of history and within modern culture, the fields of science and religion appear to be competing for the same holds in a person’s belief system. Universities are where academics and the sciences are the prevailing held truth, while in churches, the Bible reigns as supreme authority. However, in a Christian academic setting, the predominate school of thought in belief systems might turn into a little more of a melting pot. By analyzing gathered personal data (via surveys and interviews), one can begin to piece together the predominate thoughts on the apparent conflict between religion and science …

Mid-Ir Optical Refrigeration And Radiation Balanced Lasers, Saeid Rostami

Optical Science and Engineering ETDs

This dissertation reports recent advances in mid-infrared (mid-IR) optical refrigeration and Radiation Balanced Lasers (RBLs). The first demonstration of optical refrigeration in Ho:YLF and Tm:YLF crystals as promising mid-IR laser cooling candidates is reported. Room temperature laser cooling efficiency of Tm- and Ho-doped crystals at different excitation polarization is measured and their external quantum efficiency and background absorption are extracted. Complete characterization of laser cooling samples is obtained via performing detailed low-temperature spectroscopic analysis, and their minimum achievable temperature as well as conditions to achieve laser cooling efficiency enhancement in mid-IR are investigated. By developing a Thulium-doped fiber amplifier, seeded …

Magnetic Forces In The Absence Of A Classical Magnetic Field, Ismael L. Paiva, Yakir Aharonov, Jeff Tollaksen, Mordecai Waegell

Mathematics, Physics, and Computer Science Faculty Articles and Research

It is shown that, in some cases, the effect of discrete distributions of flux lines in quantum mechanics can be associated with the effect of continuous distributions of magnetic fields with special symmetries. In particular, flux lines with an arbitrary value of magnetic flux can be used to create energetic barriers, which can be used to confine quantum systems in specially designed configurations. This generalizes a previous work where such energy barriers arose from flux lines with half-integer fluxons. Furthermore, it is shown how the Landau levels can be obtained from a two-dimensional grid of flux lines. These results suggest …

Growth And Characterization Of 2d Layered Materials, Algene Fryer Ii

USF Tampa Graduate Theses and Dissertations

2D layered materials are becoming an important area of research due to their exceptional electrical and optical properties. Specifically, 2D layered monochalcogenides are known for their high carrier motilities, whereas layered metal halides have been shown to have noteworthy photoresponsivity. Despite the assortment of 2D layered materials, the search for reliable and scalable synthesis methods is still a challenge in this family of materials. Often a certain growth technique will compromise a desirable trait needed for further fabrication, such as the quality of the crystal or its coverage on a substrate. In this study, two growth techniques that incorporate changeable …

Size-Controlled Synthesis Of Nickel Nanoparticles Enclosed In Carbon Nanocages, Felicity Peebles, Grigorii Rudakov, Gamini U. Sumanasekera

Undergraduate Arts and Research Showcase

We have demonstrated a simple, scalable, and tunable method of obtaining densely packed Ni Nanoparticles encapsulated in Carbon Nanocages (Ni@CNCs). Using a facile method, it was shown that via a simple annealing process of precursor based on nickel acetate and citric acid, Ni@CNCs with sizes varying from 5 to 20 nm can be synthesized by changing the heating ramp rate during the synthesis from 25 to 53 °C/min. The final temperature of 600 °C was held for 10 min, and was the same for all the samples. X-Ray Diffraction (XRD) multiple peaks analysis was performed to show large Ni nanoparticles …

Questaal: A Package Of Electronic Structure Methods Based On The Linear Muffin-Tin Orbital Technique, Dimitar Pashov, Swagata Acharya, Walter R.L. Lambrecht, Jerome Jackson, Kirill Belashchenko, Athanasios Chantis, Francois Jamet, Mark Van Schilfgaarde

Kirill Belashchenko Publications

This paper summarises the theory and functionality behind Questaal, an open-source suite of codes for calculating the electronic structure and related properties of materials from first principles. The formalism of the linearised muffin-tin orbital (LMTO) method is revisited in detail and developed further by the introduction of short-ranged tight-binding basis functions for full-potential calculations. The LMTO method is presented in both Green's function and wave function formulations for bulk and layered systems. The suite's full-potential LMTO code uses a sophisticated basis and augmentation method that allows an efficient and precise solution to the band problem at different levels of theory, …

Investigation Of Complex Magnetic Phenomena In Spinel Femn2o4, Mnfe2o4, And Nife2o4, Roshan Kumar Nepal

LSU Doctoral Dissertations

Frustrated magnetic systems, where all spin interactions cannot be simultaneously satisfied, have continued to attract interest due to a plethora of novel magnetic states that emerge in them due to frustration and their potential technological applications. Spinel oxides AB₂O₄, where A and B are metal ions) are an excellent testing ground for the exploration of frustrated magnetism. This dissertation presents the experimental investigation of complex magnetic phenomena in the spinel oxides FeMn₂O₄, MnFe₂O₄, and NiFe₂O₄.

FeMn₂O₄ and MnFe₂O_{4 …}

Experimental Investigation Of The Secondary And Backscatter Electron Emission From New Spacecraft Surface Materials, Millan F. Diaz-Aguado, John W. Bonnell, Stuart D. Bale, Justin Christensen, Phillip Lundgreen, Jordan Lee, Jr Dennison, Justin Dekany, Brian Wood, Mike Gruntman

Journal Articles

The emission of secondary and backscattered electrons influences spacecraft surface potentials and the surrounding plasma. Modern spacecraft use new materials for which secondary emission properties have been unavailable. In this work, the total electron yield (i.e., the sum of secondary and backscattered electron yields) was measured for niobium-C103 alloy, molybdenum Titanium, Zirconium, Molybdenum (TZM) alloy, tantalum-tungsten alloy, Elgiloy®, graphite lubricant (DAG 213®), and titanium nitride. The surface properties of tungsten were also measured for comparison with past test data. The materials were readied as spacecraft flight materials and temperature-treated ("annealed") to predicted peak flight temperatures. The yield properties for 10 …

The Emergence Of The Local Moment Molecular Spin Transistor, Guanhua Hao, Ruihua Cheng, Peter Dowben

Peter Dowben Publications

Local moment molecular systems have now been used as the conduction channel in gated spintronics devices, and some of these three terminal devices might even be considered molecular spin transistors. In these systems, the gate voltage can be used to tune the molecular level alignment, while applied magnetic fields have an influence on the spin state, altering the magnetic properties, and providing insights to the magnetic anisotropy. More recently, the use of molecular spin crossover complexes, as the conduction channel, has led to devices that are both nonvolatile and have functionality at higher temperatures. Indeed, some devices have now been …

Probing Ferroelectricity By X-Ray Absorption Spectroscopy In Molecular Crystals, Fujie Tang, Xuanyuan Jiang, Hsin Yu Ko, Jianhang Xu, Mehmet Topsakal, Guanhua Hao, Alpha T. N'Diaye, Peter Dowben, Deyu Lu, Xiaoshan Xu, Xifan Wu

Peter Dowben Publications

We carry out X-ray absorption spectroscopy experiment at the oxygen K edge in croconic acid (C₅H₂O₅) crystal as a prototype of ferroelectric organic molecular solid, whose electric polarization is generated by proton transfer. The experimental spectrum is well reproduced by the electron-hole excitation theory simulations from configuration generated by ab initio molecular dynamics simulation. When inversion symmetry is broken in the ferroelectric state, the hydrogen bonding environment on the two bonded molecules become inequivalent. Such a difference is sensitively probed by the bound excitation in the pre-edge, which is strongly localized on the excited …

Thermodynamic Properties Of Transverse Field Quantum Ising Model Using Tensor Network Formalism, Sin Yang Pang

Student Works (2020-2029)

Ising model has been successful in describing ferromagnetism and its phase transition to paramagnet. At the critical point, the free energy density function and its derivatives diverge. Their behaviour near the critical point are described by power-laws with associated critical exponents. In many cases, the critical exponents can be determined from analytic solutions via conventional renormalization groups methods or from Monte Carlo simulations. However, for quantum many-body systems, very few are tractable to analytical solutions. The quantum many-body wavefunction belongs to large dimensional Hilbert space that increases exponentially with system size. If the Hamiltonian is gapped and only local interaction …

Infrared-Active Phonon Modes In Single-Crystal Thorium Dioxide And Uranium Dioxide, Sean Knight, Rafal Korlacki, Christina Dugan, James C. Petrosky, Alyssa Lynn Mock, Peter A. Dowben, J. Matthew Mann, Martin M. Kimani, Mathias Schubert

Department of Electrical and Computer Engineering: Faculty Publications

The infrared-active phonon modes, in single-crystal samples of thorium dioxide (ThO₂) and uranium dioxide (UO₂), were investigated using spectroscopic ellipsometry and compared with density functional theory. Both ThO₂ and UO₂ are found to have one infrared-active phonon mode pair [consisting of one transverse optic (TO) and one associated longitudinal optic (LO) mode], which is responsible for the dominant features in the ellipsometric data. At room temperature, our results for the mode pair’s resonant frequencies and broadening parameters are comparable with previous reflectance spectroscopy characterizations and density functional theory predictions. For ThO₂, our …

Effects Of Intrinsic Defects And Alloying With Fe On The Half-Metallicity Of Co2Mnsi, G. G. Baez Flores, Ivan A. Zhuravlev, Kirill Belashchenko

Kirill Belashchenko Publications

The electronic structure and half-metallic gap of Co2MnSi in the presence of crystallographic defects, partial Fe substitution for Mn, and thermal spin fluctuations are studied using the coherent potential approximation and the disordered local moment method. In the presence of 5% Co or Mn vacancies the Fermi level shifts down to the minority-spin valence-band maximum. In contrast to NiMnSb, both types of Mn antisite defects in Co2MnSi are strongly exchange coupled to the host magnetization, and thermal spin fluctuations do not strongly affect the half-metallic gap. Partial substitution of Mn by Fe results in considerable changes in the Bloch spectral …

Electron-Induced Massive Dynamics Of Magnetic Domain Walls, Hilary M. Hurst, Victor Galitski, Tero T. Heikkilä

Faculty Research, Scholarly, and Creative Activity

We study the dynamics of domain walls (DWs) in a metallic, ferromagnetic nanowire. We develop a Keldysh collective coordinate technique to describe the effect of conduction electrons on rigid magnetic structures. The effective Lagrangian and Langevin equations of motion for a DW are derived. The DW dynamics is described by two collective degrees of freedom: position and tilt-angle. The coupled Langevin equations therefore involve two correlated noise sources, leading to a generalized fluctuation-dissipation theorem (FDT). The DW response kernel due to electrons contains two parts: one related to dissipation via FDT, and another `inertial' part. We prove that the latter …