Condensed Matter Physics Commons^™

Linear And Non Linear Properties Of Two-Dimensional Exciton-Polaritons, Mandeep Khatoniar

Dissertations, Theses, and Capstone Projects

Technology has been accelerating at breakneck speed since the first quantum revolution, an era that ushered transistors and lasers in the late 1940s and early 1960s. Both of these technologies relied on a matured understanding of quantum theories and since their inception has propelled innovation and development in various sectors like communications, metrology, and sensing. Optical technologies were thought to be the game changers in terms of logic and computing operations, with the elevator pitch being "computing at speed of light", a fundamental speed limit imposed by this universe’s legal system (a.k.a physics). However, it was soon realized that that …

Topological Classical Wave Systems With Modulations, Interactions, And Higher-Order Topological States, Mengyao Li

Dissertations, Theses, and Capstone Projects

Topological phases in classical wave systems, such as photonic and acoustic, have been actively investigated and applied for wave guiding, lasing, and numerous other novel phenomena and device applications Topological phase transitions enable robust boundary states, and the field has been broadening recently into a vast variety of systems with temporal modulations and interactions. Floquet modulation, for example, is the modulation applied periodically in time which may break symmetries and leads to novel topological phases.

Introducing non-Hermitian Floquet modulation enables more interesting phenomena including bandgap in imaginary part of the spectrum and gainy/lossy topological edge states with complex energy values. …

Developing Dynamical Probes Of Quantum Spin Liquids Inspired By Techniques From Spintronics, Joshua Aftergood

Dissertations, Theses, and Capstone Projects

We theoretically study low dimensional insulating spin systems using spin fluctuations as a probe of the spin dynamics. In some systems, low dimensionality in conjunction with other quantum fluctuation enhancing effects impedes spontaneous generation of long range magnetic ordering down to zero absolute temperature. In particular, we focus on exotic spin systems hosting mobile, fractionalized spin excitations above their ground state, and ultimately show that techniques already commonplace in spintronics can be utilized in the context of quantum magnetism to develop probes of exotic ground states.

We initially consider quantum spin chains (QSCs), and examine a system of two exchange-coupled …

Wave Excitation And Dynamics In Disordered Systems, Yiming Huang

Dissertations, Theses, and Capstone Projects

This thesis presents studies of the field and energy excited in disordered systems as well as the dynamics of scattering.

Dynamic and steady state aspects of wave propagation are deeply connected in lossless open systems in which the scattering matrix is unitary. There is then an equivalence among the energy excited within the medium through all channels, the Wigner time delay, which is the sum of dwell times in all channels coupled to the medium, and the density of states. But these equivalences fall away in the presence of material loss or gain. In this paper, we use microwave measurements, …

Nonlinear Optical Studies Of Interfacial Ferroelectricity And Strain Distribution In Perovskite Dielectric Films, Tony Le

Dissertations, Theses, and Capstone Projects

Dielectric and ferroelectric perovskite films have been model energy storage structures for their low-dielectric loss, extremely high charge-discharge speed, and good temperature stability, yet there is still much to understand about the material’s limitations. This dissertation presents a detailed understanding of the strain-induced ferroelectricity at the boundary between a strontium titanate (SrTiO₃) ultrathin film epitaxially grown on a germanium (Ge) substrate through optical second harmonic generation (SHG), and the polydomain distribution in the Zr-doped BaTiO₃ (BZT) films by time-resolved pump-probe spectroscopy.

First, SHG measurements were performed to reveal interfacial ferroelectricity in the epitaxial SrTiO₃/Ge (100) …

Spontaneous Fluctuations In A Magnetic Fe/Gd Skyrmion Lattice, M. H. Seaberg, B. Holladay, S. A. Montoya, X. Y. Zheng, J. C.T. Lee, A. H. Reid, J. D. Koralek, L. Shen, V. Esposito, G. Coslovich, P. Walter, S. Zohar, V. Thampy, M. F. Lin, P. Hart, K. Nakahara, R. Streubel, S. D. Kevan, P. Fischer, W. Colocho, A. Lutman, F. J. Decker, E. E. Fullerton, M. Dunne, S. Roy, S. K. Sinha, J. J. Turner

Robert Streubel Papers

Magnetic skyrmions are topological spin textures that exhibit classical or quantum quasiparticle behavior. A substantial amount of research has occurred in this field, both because of their unique electromagnetic properties and potential application for future nonvolatile memory storage applications, as well as fundamental questions on their topology and unique magnetic phases. Here, we investigate the fluctuation properties of a magnetic Fe/Gd skyrmion lattice, using short-pulsed x rays. We first measure spontaneous fluctuations of the skyrmion lattice phase and find an inherent, collective mode showing an underdamped oscillation with a relaxation of a couple of nanoseconds. Further observations track the response …

Physical Properties Of Polar Magnetic Oxides Hofewo6

Symposium of Student Scholars

Polar magnetic oxides are interesting systems to study due to the possibility of hosting functional properties such as ferroelectricity, piezoelectricity, etc. In this work, a new compound HoFeWO₆ is synthesized using high-temperature solid-state reaction and characterized using x-ray diffraction, neutron diffraction, magnetization measurements, and dielectric measurements. The x-ray and neutron diffraction results indicate that HoFeWO₆ crystallizes in polar (non-centrosymmetric and achiral) orthorhombic structure P n a 21. The magnetization measurements indicate that HoFeWO₆ exhibit paramagnetic to antiferromagnetic transition at T_N = 18 K. The dielectric properties at room temperature indicate that the dielectric constant decreases with …

Effects Of Structure, Crystallographic Orientation, And Dimensionality On Emergent Properties Of Transition Metal Oxide Thin Films, Prahald Siwakoti

LSU Doctoral Dissertations

SrRuO₃ is the only example of ferromagnetic perovskite oxide of a 4d transition metal, wherein the electron -electron correlation is still relevant while the heavier 4d ion (Ru) gives it a larger spin-orbit coupling strength which makes it an interesting material to study. In this thesis, we present our investigation of the structure and properties of SrRuO₃ thin films of varying thickness grown on [001] and [111] crystallographic orientation of the SrTiO3 substrate. For SrRuO₃(001), we present microscopically the presence of 90◦ in-plane rotated structural domains that are identified by the difference in octahedral rotations and …

Photoluminescence Spectra Of Silicon Doped With Cadmium, N A. Sultanov, E T. Rakhimov, Z Mirzajonov, F T. Yusupov

Scientific-technical journal

Cadmium and zinc, as transition metals, are deep-level impurities (DL) and have a significant effect on the electrical, photoelectric, recombination, and other properties of semiconductor crystals.This paper presents the results of experimental studies of the optical and electrical properties of silicon crystals containing impurity atoms of cadmium and zinc using DLTS and low-temperature photoluminescence (PL).

Vortex-Oriented Ferroelectric Domains In Snte/Pbte Monolayer Lateral Heterostructures, Kai Chang, John W. D. Villanova, Jing-Rong Ji, Souvik Das, Felix Kuster, Salvador Barraza-Lopez, Paolo Sessi, Stuart S. P. Parkin

Physics Faculty Publications and Presentations

Heterostructures formed from interfaces between materials with complementary properties often display unconventional physics. Of especial interest are heterostructures formed with ferroelectric materials. These are mostly formed by combining thin layers in vertical stacks. Here the first in situ molecular beam epitaxial growth and scanning tunneling microscopy characterization of atomically sharp lateral heterostructures between a ferroelectric SnTe monolayer and a paraelectric PbTe monolayer are reported. The bias voltage dependence of the apparent heights of SnTe and PbTe monolayers, which are closely related to the type-II band alignment of the heterostructure, is investigated. Remarkably, it is discovered that the ferroelectric domains in …

Sawtooth-Based Chromate Multiferroic - Insight Into Structure And Magnetism, Hector Cein Mandujano

Open Access Theses & Dissertations

The coexistence of two order parameters is a particular occurrence in bulk single-phase materials. Such materials possessing (anti)ferromagnetism, ferroelectricity, and ferroelasticity are known as multiferroics. In this work we revisit BeCr2O4, which is one of the oldest material to be studied in this context. Cr3+ occupies octahedral 4a site and Be2+ occupies tetrahedral 4c site in this compound, forming a close packing structure with a 90° and 138° Cr-O-Cr bonds allowing magnetic superexchange interactions. In the present work, BeCr2O4 powder was prepared using solid-state reaction method and the crystal structure was studied in detail using laboratory and synchrotron X-ray diffraction. …

Transport Properties Of Binary And Doped Diborides, Alin Babu Niraula

Graduate Theses/Dissertations

A systematic computational study to evaluate the electronic structures and transport properties including resistivity, thermal conductivity of several binary diborides (ZrB2 , TiB2 , TaB2 , CrB2 , and AlB2 ) and the ZrB2 alloyed with Cr, Al, Ti and Ta has been performed. Due to the p-d hybridization, the characteristic pseudo gap at the Fermi energy level (Ef) from the density of states (DOS) is presence in the DOS of both ZrB2 and TiB2 in contrast to those of TaB2 and CrB2 with only a partial occupation on the anti-bonding states. AlB2 is also similarly shown the presence of …

Voltage-Controlled Magnetization In Chromia-Based Magnetic Heterostructures, William Echtenkamp

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

Spintronics promises a new generation of low-power, high-speed, non-volatile memory and logic devices. Heterostructures based on magnetoelectric chromia enable the direct manipulation of magnetization by applied electric fields and emerged as a promising building block for spintronic devices. In this dissertation, several interesting emergent magnetic properties arising in these device-enabling building blocks are examined. In some cases, exchange coupling at the interface between the magnetoelectric antiferromagnet and an adjacent ferromagnet stabilizes the interfacial antiferromagnetic domain state against the electrically induced rotation of the bulk spin structure. Upon magnetically cycling the ferromagnet, the magnetoelectric antiferromagnet relaxes towards a commensurate spin structure …

Manipulation Of Spin Crossover Phenomenon In An Fe(Ii) Molecular Complex And Application To Molecular Spintronics, Guanhua Hao

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

Molecules with a large local magnetic moment have attracted considerable attention for application in spintronic devices. One candidate of a suitable device goes to the spin crossover molecule, where these 3d transition metal compounds are able to exhibit a robust spin state transition between distinct states. By proper design, the spintronic devices fabricated via spin crossover molecular thin films could achieve novel functionality while retaining flexibility and other traits based on its “organic” nature.

Controlling the spin state transition is a key factor of these possibilities. This thesis work investigates the manipulation of the spin state transition in [Fe{H …

Structural, Vibrational And Transport Properties Of Novel Complex Systems., Bhupendra Man Shing Karki

Electronic Theses and Dissertations

Electron correlation effects in quantum materials are very strong. It is critical to investigate the structure of quantum materials to better understand and manipulate their physical properties. Quantum effects are prominent at the atomic microscopic length scale, which can not be examined by average long range structural measurements using traditional diffraction methods. Instead, pair distribution function (PDF) analysis, a local structure probe, can effectively unveil the mystery of local structure, which is more sensitive to local behavior than bulk average features. The first section of my dissertation will concentrate on the local structural study of the Iron oxy-chalcogenides, {\cSSe}, which …

Intercalation And High Pressure Studies Of Black Phosphorous - Pathways To Novel Materials And Physics., Manthila Chathurange Rajapakse

Electronic Theses and Dissertations

Discovery of graphene in 2004 initiated a new trend of materials known as two-dimensional (2D) materials which have exciting surface properties and anisotropies than their bulk counterparts. Phosphorene, which is the layered version of black phosphorous (BP) is one of the top 2D materials in terms of research interests and applications of the present day. Moving a step further, our interest is to understand the possibilities for structural modifications of phosphorene, by means of stimuli such as intercalation and high-pressure. It has been predicted by theoretical studies that these stimuli may lead to the formation of new structures and phases …

Study Of Weakly Bound Cluster Anions Using Self Interaction Corrected Density Functional Scheme, Peter Obinna Ufondu

Open Access Theses & Dissertations

The Kohn–Sham formulation of density functional theory (DFT) is a widely used quantum mechanical theory to study chemical and materials properties. The practical application of DFT requires an approximation to the exchange–correlation (XC) functional. These approximations suffer from self-interaction errors due to the incomplete cancellation of the self-Coulomb energy with the approximate self-exchange and correlation energy for one-electron densities. Systems with weakly-bound electrons impose great challenges to semi-local density functional approximations. We use recently developed local scaled self-interaction correction (LSIC) by Zope et al and the Perdew-Zunger SIC method using the Fermi-Löwdin orbitals to calculate the vertical detachment energies (VDEs) …

On-Chip Terahertz Time-Domain Spectroscopy, Randy Sterbentz

UNLV Theses, Dissertations, Professional Papers, and Capstones

Terahertz time-domain spectroscopy (THz-TDS) allows the direct measurement of optical and charge carrier properties of materials in a region of the electromagnetic spectrum inaccessible to most other spectroscopic techniques. We have adapted the technique to an on-chip arrangement that allows us to measure these properties in nanoscale materials with dimensions below the diffraction limit. In this thesis, we present the operation of instruments and the mechanics behind performing on-chip terahertz time-domain spectroscopy. Three materials were tested to confirm the capabilities of our system to measure THz radiation: indium selenide (InSe), radiation-damaged silicon-on-sapphire (RD-SOS), and an erbium arsenide:gallium arsenide superlattice. Preliminary …

Computational Studies Of Carbon Nanocluster Solidification, Chathuri C. Silva

Dissertations

A subset of micron-size meteoritic carbon particles formed in red giant atmospheres show a core-rim structure, likely condensed from a vapor phase into super-cooled carbon droplets that nucleated graphene sheets (~40Å) on randomly oriented 5-atom loops during solidification, followed by coating with a graphite rim. Similar particles form during slow cooling of carbon vapor in the lab.

Here we investigate the nucleation and growth of carbon rings and graphene sheets using density functional theory (DFT). Our objectives: (1). explore different computational techniques in DFT-VASP for various carbon structures and compare the results with literature, (2). investigate the nucleation and growth …

Photovoltages In Polycrystalline Mosaic Solar Cells, Steluta A. Dinca, Eric A. Schiff

Chemistry - All Scholarship

In some thin-film solar cells the light-absorbing layer is a mosaic of crystalline grains whose boundaries run from the back to the front of the cell. We used the semiconductor modeling software Sesame to do numerical calculations of the optoelectronic properties of such cells assuming that recombination of minority photocarriers occurs primarily at the grain boundaries. The work complements analytical results for diffusion-limited recombination at grain boundaries and dislocations. We chose idealized n-CdS/p-CdTe solar cells for illustration. We find that the open-circuit voltage, V_oc, under illumination declines logarithmically with increasing ratio D/θ², where D is the …