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Competing And Cooperating Orders In The Three-Band Hubbard Model: A Comprehensive Quantum Monte Carlo And Generalized Hartree-Fock Study, Adam Chiciak 2020 William & Mary - Arts & Sciences

Competing And Cooperating Orders In The Three-Band Hubbard Model: A Comprehensive Quantum Monte Carlo And Generalized Hartree-Fock Study, Adam Chiciak

Dissertations, Theses, and Masters Projects

Significant progress has been made in studying strongly correlated electronic systems with major focus on understanding high-temperature superconductivity. At the center of these studies are the so-called cuprates, which are characterized by a quasi-2D Copper-Oxide plane in which superconductivity is believed to arise. From the theoretical point of view, the complex electronic structure of these materials makes a fully ab initio many-body computation a formidable task, so we are forced to focus on minimal models that can reproduce the physics, the most well known of which is known as the Hubbard Model, which relies on the Zhang-Rice singet notion to ...


Growth Engineering And Characterization Of Vanadium Dioxide Films For Ultraviolet Detection, Jason Andrew Creeden 2020 William & Mary - Arts & Sciences

Growth Engineering And Characterization Of Vanadium Dioxide Films For Ultraviolet Detection, Jason Andrew Creeden

Dissertations, Theses, and Masters Projects

There is a need for efficient ultraviolet (UV) detectors in many fields, such as aerospace, automotive manufacturing, biology, environmental science, and defense, due to photomultiplier tubes (the currently available technology) often not meeting application constraints in weight, robustness, and power consumption. In my thesis, I demonstrate that high quality vanadium dioxide (VO2) thin films, epitaxially grown on niobium doped titanium dioxide substrates (TiO2:Nb), display a strong photoconductive response in the UV spectral range, making them promising candidates for photomultiplier-free UV photodetection. By adjusting the characteristics of the substrate and VO2 film, the samples achieve external quantum efficiency exceeding 100 ...


On Demand Nanoscale Phase Manipulation Of Vanadium Dioxide By Scanning Probe Lithography, Dustin Schrecongost 2020 West Virginia University

On Demand Nanoscale Phase Manipulation Of Vanadium Dioxide By Scanning Probe Lithography, Dustin Schrecongost

Graduate Theses, Dissertations, and Problem Reports

This dissertation focuses on nanoscale phase manipulations of Vanadium Dioxide. Nanoscale control of material properties is a current obstacle for the next generation of optoelectronic and photonic devices. Vanadium Dioxide is a strongly correlated material with an insulator-metal phase transition at approximately 345 K that generates dramatic electronic and optical property changes. However, the development of industry device application based on this phenomenon has been limited thus far due to the macroscopic scale and the volatile nature of the phase transition. In this work these limitations are assessed and circumvented.

A home-built, variable temperature, scanning near-field optical microscope was engineered ...


Insulator To Metal Transition Dynamics Of Vanadium Dioxide Thin Films, Scott Madaras 2020 William & Mary - Arts & Sciences

Insulator To Metal Transition Dynamics Of Vanadium Dioxide Thin Films, Scott Madaras

Dissertations, Theses, and Masters Projects

Vanadium Dioxide (VO2) is a strongly correlated material which has been studied for many decades. VO2 has been proposed for uses in technologies such as optical modulators, IR modulators, optical switches and Mott memory devices. These technologies are taking advantage of VO2’s insulator to metal transition (IMT) and the corresponding changes to the optical and material properties. The insulator to metal transition in VO2 can be accessed by thermal heating, applied electric field, or ultra-fast photo induced processes. Recently, thin films of VO2 grown on Titanium Dioxide doped with Niobium (TiO2:Nb), have shown promise as a possible UV ...


A First-Principles Study Of The Nature Of The Insulating Gap In Vo2, Christopher Hendriks 2020 William & Mary - Arts & Sciences

A First-Principles Study Of The Nature Of The Insulating Gap In Vo2, Christopher Hendriks

Dissertations, Theses, and Masters Projects

Upon cooling past a critical temperature Tc = 340 K Vanadium dioxide (VO2) exhibits a metal-insulator transition (MIT) from a metallic rutile R to an insulating monoclinic M1 phase. Other insulating phases, a monoclinic M2 and triclinic T, have been identifed and are accessible via strain or doping. Despite decades of research, the nature of the VO2 MIT is still not fully understood. In this work we present ab-initio hybrid density functional theory (DFT) calculations on the insulating phases, compare the results to experimental measurements and discuss their implications on our understanding of the VO2 MIT. Recent measurements on M1 VO2 ...


Electric Field Control Of Fixed Magnetic Skyrmions For Energy Efficient Nanomagnetic Memory, Dhritiman Bhattacharya 2020 Virginia Commonwealth University

Electric Field Control Of Fixed Magnetic Skyrmions For Energy Efficient Nanomagnetic Memory, Dhritiman Bhattacharya

Theses and Dissertations

To meet the ever-growing demand of faster and smaller computers, increasing number of transistors are needed in the same chip area. Unfortunately, Silicon based transistors have almost reached their miniaturization limits mainly due to excessive heat generation. Nanomagnetic devices are one of the most promising alternatives of CMOS. In nanomagnetic devices, electron spin, instead of charge, is the information carrier. Hence, these devices are non-volatile: information can be stored in these devices without needing any external power which could enable computing architectures beyond traditional von-Neumann computing. Additionally, these devices are also expected to be more energy efficient than CMOS devices ...


Magnetism In Γ-Fesi2 Nanostructures: A First Principles Study, Sahil Dhoka 2020 Michigan Technological University

Magnetism In Γ-Fesi2 Nanostructures: A First Principles Study, Sahil Dhoka

Dissertations, Master's Theses and Master's Reports

First-principles calculations are performed on γ-FeSi2 nanostructures grown on Si (111) and (001) substrate. An attempt to explain the origin of emergent magnetic properties of the metastable gamma phase of iron di-silicide (γ-FeSi2) is made, which show ferromagnetic behavior on nanoscale, unlike its possible bulk form. Many papers try to explain this magnetism from factors like bulk, epitaxial strain, interface, surface, edges, and corners but doesn’t provide an analytical study for these explanations. Density functional theory is used to analyze the magnetic effects of these factors. The results for the epitaxial structures show no magnetic behavior for ...


Electrodynamics Modeling Of Plasmonic-Organic Hybrid Waveguides, Marcus Michel 2020 Claremont Colleges

Electrodynamics Modeling Of Plasmonic-Organic Hybrid Waveguides, Marcus Michel

Pomona Senior Theses

Optical fibers have multiple advantages over conventional electrical connections, such as lower energy losses and higher bandwidth. To use optics for chip-to-chip communication, electro-optic (EO) modulators need to be scaled down to be incorporated on integrated circuits. This size reduction has been accomplished using plasmonic-organic hybrid (POH) waveguides, which make use of nonlinear organic EO materials and surface plasmon polaritons to achieve light modulation in devices with lengths on the micron scale. As these devices are just starting to be developed, there are many avenues for their potential optimization. In order to streamline and reduce the cost of the optimization ...


Ferromagnetic Spin Fluctuations In The Filled Skutterudite Compounds, Cheng Xiang 2020 Iowa State University

Ferromagnetic Spin Fluctuations In The Filled Skutterudite Compounds, Cheng Xiang

Creative Components

Introduce the ferromagnetic spin fluctuations in the filled skutterudite compounds, SrFe4As12 and SrOs4As12, and analyze further applied pressure data.


Experimental And Computational Exploration Of The Dilute Magnetic Delafossite Cual1-Xfexo2 Alloys, Mina Aziziha 2020 West Virginia University

Experimental And Computational Exploration Of The Dilute Magnetic Delafossite Cual1-Xfexo2 Alloys, Mina Aziziha

Graduate Theses, Dissertations, and Problem Reports

CuAlO2 is among several ternary delafossites, which is a rare p-type semiconductor with potential applications as a transparent conductive oxide, photocatalyst, and spintronics when doped with transition metal ions. Reported in this thesis are results from our investigations of CuAl1-xFexO2 (x = 0 to1) with a focus on the x-dependence of structural, magnetic, vibrational, optical properties, and the role of defects and impurities. Samples are prepared by solid-state reactions.

We performed a complete study of magnetic properties to investigate the possibility of room temperature ferromagnetic alloys, which are used in transparent ferromagnet ...


Fifth-Degree Elastic Potential For Predictive Stress-Strain Relations And Elastic Instabilities Under Large Strain And Complex Loading In Si, Hao Chen, Nikolai A. Zarkevich, Valery I. Levitas, Duane D. Johnson, Xiancheng Zhang 2020 East China University of Science and Technology and Iowa State University

Fifth-Degree Elastic Potential For Predictive Stress-Strain Relations And Elastic Instabilities Under Large Strain And Complex Loading In Si, Hao Chen, Nikolai A. Zarkevich, Valery I. Levitas, Duane D. Johnson, Xiancheng Zhang

Aerospace Engineering Publications

Materials under complex loading develop large strains and often transition via an elastic instability, as observed in both simple and complex systems. Here, we present Si I under large strain in terms of Lagrangian strain by an 5th-order elastic potential found by minimizing error relative to density functional theory (DFT) results. The Cauchy stress-Lagrangian strain curves for arbitrary complex loadings are in excellent correspondence with DFT results, including elastic instability driving Si I→II phase transformation (PT) and the shear instabilities. PT conditions for Si I→II under action of cubic axial stresses are linear in Cauchy stresses in agreement ...


Reply To “Comment On ‘Magnetic Structure And Magnetization Of Z-Axis Helical Heisenberg Antiferromagnets With Xy Anisotropy In High Magnetic Fields Transverse To The Helix Axis At Zero Temperature’ ”, David C. Johnston 2020 Iowa State University and Ames Laboratory

Reply To “Comment On ‘Magnetic Structure And Magnetization Of Z-Axis Helical Heisenberg Antiferromagnets With Xy Anisotropy In High Magnetic Fields Transverse To The Helix Axis At Zero Temperature’ ”, David C. Johnston

Ames Laboratory Accepted Manuscripts

The Comment criticizes the assumptions of the model I used. I was aware of the limitations of my model. However, my model is useful for fitting high-field magnetization versus transverse-field data for real helical Heisenberg antiferromagnets at temperatures much lower than their Néel temperatures and estimating their critical fields. To my knowledge, there existed no prior theory that could fit such experimental data over the entire field range of experiments. I welcome that the Comment calls for more accurate theory.


Quantum Phase Transition Inside The Superconducting Dome Of Ba(Fe1-Xcox)2as2 From Diamond-Based Optical Magnetometry, Kamal R. Joshi, Naufer Nusran, Makariy A. Tanatar, Kyuil Cho, Sergey L. Bud’ko, Paul C. Canfield, R. M. Fernandes, A. Levchenko, Ruslan Prozorov 2020 Iowa State University and Ames Laboratory

Quantum Phase Transition Inside The Superconducting Dome Of Ba(Fe1-Xcox)2as2 From Diamond-Based Optical Magnetometry, Kamal R. Joshi, Naufer Nusran, Makariy A. Tanatar, Kyuil Cho, Sergey L. Bud’Ko, Paul C. Canfield, R. M. Fernandes, A. Levchenko, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

Unconventional superconductivity often emerges in close proximity to a magnetic instability. Upon suppressing the magnetic transition down to zero temperature by tuning the carrier concentration, pressure, or disorder, the superconducting transition temperature $T_c$ acquires its maximum value. A major challenge is the elucidation of the relationship between the superconducting phase and the strong quantum fluctuations expected near a quantum phase transition (QPT) that is either second order (i.e. a quantum critical point) or weakly first order. While unusual normal state properties, such as non-Fermi liquid behavior of the resistivity, are commonly associated with strong quantum fluctuations, evidence for its ...


Investigating The Time Scales Of Electromechanical Motion In Graphene Drumheads Using Pump-Probe Spectroscopy With Stm, Alana P. Gudinas 2020 University of New Hampshire, Durham

Investigating The Time Scales Of Electromechanical Motion In Graphene Drumheads Using Pump-Probe Spectroscopy With Stm, Alana P. Gudinas

Honors Theses and Capstones

Scanning tunneling microscopy (STM) has transformed the field of condensed matter physics over the past few decades, allowing scientists to image materials at the atmomic scale, manipulate individual atoms, and probe electronic states on the surface of materials. In recent years, there have been numerous developments to introduce time-resolved measurements to STM in order to probe atomic-scale dynamic processes and combine spatial and temporal resolution. Advances like THz-STM setups achieve femtosecond resolution, but require complex external setups. All-electronic pump-probe spectroscopy for STM (directly analogous to optical pump-probe spectroscopy) has been pioneered by Loth et al., and newer applications (Natterer et ...


Quantum Phases And Phase Transitions In Designer Spin Models, Nisheeta Desai 2020 University of Kentucky

Quantum Phases And Phase Transitions In Designer Spin Models, Nisheeta Desai

Theses and Dissertations--Physics and Astronomy

This work focuses on numerical studies of quantum spin systems. These simple models are known to exhibit a variety of phases, some of which have no classical counterpart. Phase transitions between them are driven by quantum fluctuations and the unconventional nature of some such transitions make them a fascinating avenue of study.

Quantum Monte Carlo (QMC) is an indispensable tool in the study of these phases and phase transitions in two and higher dimensions. Nevertheless, we are limited by our inability to simulate models that suffer from the infamous sign problem. While the case of S=1/2 has been ...


Transverse And Longitudinal Thermal Diffusivity Measurements Of Polymer And Small Molecule Organic Semiconductors With Different Techniques, Maryam Shahi 2020 University of Kentucky

Transverse And Longitudinal Thermal Diffusivity Measurements Of Polymer And Small Molecule Organic Semiconductors With Different Techniques, Maryam Shahi

Theses and Dissertations--Physics and Astronomy

The main thrust of this research was to develop new probes to measure thermal conductivities (κ) of small-molecule crystals, as well as polymer blends of organic semiconductors, both to screen these for possible applications, e.g. as thermoelectric power generators, and to gain an understanding of thermal transport in them. Emphasis has been on the crystals of “TIPS pentacene” [TIPS = 6,13 bis(triisopropylsilylethynyl), and free-standing films of PEDOT:PSS [poly(3,4-ethylenedioxythiophene) polystyrene sulfonate] for different electrochemical and thermoelectric applications. Separate techniques were used for in-plane and transverse thermal conductivities in which 𝜅𝜅 is determined indirectly from measurements of ...


Remark On Lehnert’S Revised Quantum Electrodynamics (Rqed) As An Alternative To Francesco Celani’S Et Al. Maxwell-Clifford Equations: With An Outline Of Chiral Cosmology Model And Its Role To Cmns, Florentin Smarandache, Victor Christianto, Yunita Umniyati 2020 University of New Mexico

Remark On Lehnert’S Revised Quantum Electrodynamics (Rqed) As An Alternative To Francesco Celani’S Et Al. Maxwell-Clifford Equations: With An Outline Of Chiral Cosmology Model And Its Role To Cmns, Florentin Smarandache, Victor Christianto, Yunita Umniyati

Mathematics and Statistics Faculty and Staff Publications

In a recent paper published in JCMNS in 2017, Francesco Celani, Di Tommaso & Vassalo argued that Maxwell equations rewritten in Clifford algebra are sufficient to describe the electron and also ultra-dense deuterium reaction process proposed by Homlid et al. Apparently, Celani et al. believed that their Maxwell-Clifford equations are an excellent candidate to surpass both Classical Electromagnetic and Zitterbewegung QM. Meanwhile, in a series of papers, Bo Lehnert proposed a novel and revised version of Quantum Electrodynamics (RQED) based on Proca equations. Therefore, in this paper, we gave an outline of Lehnert’s RQED, as an alternative framework to Celani ...


Raman Scattering From One And Two Magnons In Magnetoelectric Linipo4, D. Rigitano, David Vaknin, G. E. Barberis, E. Granado 2020 University of Campinas - UNICAMP

Raman Scattering From One And Two Magnons In Magnetoelectric Linipo4, D. Rigitano, David Vaknin, G. E. Barberis, E. Granado

Ames Laboratory Accepted Manuscripts

Polarized Raman scattering in magnetoelectric LiNiPO4 shows a sharp resonant peak at 37 cm−1 in the magnetically ordered phase, originating from a one-magnon excitation of Ni2+S=1 localized moments at the zone center. Also, a broad component with maximum intensity at ∼65cm−1 is observed and successfully modeled in terms of light scattering from two-magnon excitations within the framework of the Fleury-Loudon theory using five relevant exchange parameters, providing an independent experimental confirmation of their values previously obtained with inelastic neutron scattering data in this material. An additional peak at 58 cm−1, already reported in previous works ...


Magnetic Structure Of Selected Gd Intermetallic Alloys From First Principles, L. Petit, Z. Szotek, Durga Paudyal, Anis Biswas, Yaroslav Mudryk, Vitalij K. Pecharsky, J. B. Staunton 2020 Daresbury Laboratory

Magnetic Structure Of Selected Gd Intermetallic Alloys From First Principles, L. Petit, Z. Szotek, Durga Paudyal, Anis Biswas, Yaroslav Mudryk, Vitalij K. Pecharsky, J. B. Staunton

Ames Laboratory Accepted Manuscripts

Using first-principles calculations, based on disordered local moment (DLM) theory combined with the self-interaction corrected local spin density approximation (SIC-LSDA), we study magnetic correlations in the paramagnetic state of GdX(X=Cu, Zn, Ga, Ag, Cd, In, Au, Hg, and Tl) intermetallics and their alloys. The predicted magnetic orders and ordering temperatures that these correlations lead to are in overall good agreement with available experiments. The interactions between the Gd f-electron local moments are mediated by the valence electrons of the intermetallics which comprise both Gd and Xd bands as well as sp bands. There are RKKY-like features such as ...


Interfacial Contributions To Spin-Orbit Torque And Magnetoresistance In Ferromagnet/Heavy-Metal Bilayers, Kirill Belashchenko, Alexey Kovalev, Mark van Schilfgaarde 2020 University of Nebraska - Lincoln

Interfacial Contributions To Spin-Orbit Torque And Magnetoresistance In Ferromagnet/Heavy-Metal Bilayers, Kirill Belashchenko, Alexey Kovalev, Mark Van Schilfgaarde

Faculty Publications, Department of Physics and Astronomy

The thickness dependence of spin-orbit torque and magnetoresistance in ferromagnet/heavy-metal bilayers is studied using the first-principles nonequilibrium Green’s function formalism combined with the Anderson disorder model. A systematic expansion in orthogonal vector spherical harmonics is used for the angular dependence of the torque. The dampinglike torque in Co/Pt and Co/Au bilayers can be described as a sum of the spin-Hall contribution, which increases with thickness in agreement with the spin-diffusion model, and a comparable interfacial contribution. The magnetoconductance in the plane perpendicular to the current in Co/Pt bilayers is of the order of a conductance ...


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