Condensed Matter Physics Commons^™

Crystal Structure, Magnetism And Magnetocaloric Properties Of Mn2−XSn0.5Ga0.5 (X=0, 0.3, 0.5, 0.8) Alloys, H. Qian, Rabindra Pahari, K. Schroeder, Shah R. Valloppilly, Y. Huh, Pavel V. Lukashev, J. Hu, Parashu Kharel, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Magnetic refrigeration based on the magnetocaloric effect has attracted recent attention due to advantages such as high efficiency and environmental friendliness. We have investigated the structural, magnetic and magnetocaloric properties of Mn_2−xSn_0.5Ga_0.5 (x=0, 0.3, 0.5, 0.8) alloys prepared using arc-melting and meltspinning techniques with prospects for magnetic refrigeration. The Mn_2−xSn_0.5Ga_0.5 alloys, except for Mn_1.2Sn_0.5Ga_0.5, have a single-phase hexagonal crystal structure. The Mn_1.2Sn_0.5Ga_0.5 alloy also contains a small amount of MnSn₂ impurity phase. The Curie temperature and high-field (30 kOe) …

New Perspectives On The Schrödinger-Pauli Theory Of Electrons: Part I, Viraht Sahni

Publications and Research

Schrödinger-Pauli (SP) theory is a description of electrons in the presence of a static electromagnetic field in which the interaction of the magnetic field with both the orbital and spin moments is explicitly considered. The theory is described from the new perspective of the individual electron via its equation of motion or ‘Quantal Newtonian’ first law. The law is in terms of ‘classical’ fields whose sources are quantum mechanical expectation values of Hermitian operators taken with respect to the system wave function. The law states that each electron experiences an external and an internal field, the sum of which vanish. …

New Perspectives On The Schrödinger-Pauli Theory Of Electrons: Part Ii: Application To The Triplet State Of A Quantum Dot In A Magnetic Field, Marlina Slamet, Viraht Sahni

Publications and Research

The Schrödinger-Pauli (SP) theory of electrons in the presence of a static electromagnetic field can be described from the perspective of the individual electron via its equation of motion or 'Quantal Newtonian' first law. The law is in terms of 'classical' fields whose sources are quantum-mechanical expectation values of Hermitian operators taken with respect to the wave function. The law states that the sum of the external and internal fields experienced by each electron vanishes. The external field is the sum of the binding electrostatic and Lorentz fields. The internal field is the sum of fields representative of properties of …

Using Fundamental Properties Of Light To Investigate Photonic Effects In Condensed Matter And Biological Tissues, Laura A. Sordillo

Dissertations and Theses

Light possesses characteristics such as polarization, wavelength and coherence. The interaction of light and matter, whether in a semiconductor or in a biological sample, can reveal important information about the internal properties of a system. My thesis focuses on two areas: photocarriers in gallium arsenide and biomedical optics. Varying the excitation wavelength can be used to study both biological tissue and condensed matter. I altered the excitation wavelengths to be in the longer near-infrared (NIR) optical windows, in the shortwave infrared (SWIR) range, a wavelength region previously thought to be unusable for medical imaging. With this method, I acquired high …

Novel Computational Methods For Catalytic Applications, Gihan Uthpala Panapitiya

Graduate Theses, Dissertations, and Problem Reports (ETD)

Thiolate protected nanoclusters gold nanoparticles are gaining interest of many researchers due to their promising applications in a variety of fields the development of synthesizing techniques capable of producing atomically precise nanoclusters with high purity. Au₂₅(SR)₁₈ is one of the widely studied nanoclsuters due its remarkable stability. In this first part of this study, we explore the structural, electronic and catalytic properties of bimetallic Au_25−xAg_x(SR)₁₈ (for x = 6, 7, 8). Due to the combinatorial enormity of the total number of possible alloyed isomers, we choose a randomly selected subset corresponding to …

Depth Dependent Atomic Valence Determination In La0.7sr0.3mno3 Thin Films Using Synchrotron Techniques, Robbyn B. Trappen

Graduate Theses, Dissertations, and Problem Reports (ETD)

The valence of atoms often has a strong effect on the properties of materials, such as magnetism, conductivity, and superconductivity. The atomic valence is often perturbed at the surface and/or interface and this deviation may play a strong role in many physical phenomena such as interfacial coupling and dead layers, both magnetic and electric. In this dissertation, I present a non-destructive approach of combining two X-ray absorption detection modes, electron yield and fluorescence, with very different probing depths in conjunction with theory to map out the layer-by-layer valence of a thin film.

The weighted average Mn atomic valence as measured …

Application Of Global Search Methods To Materials Prediction And Design, Adam J. Payne

Graduate Theses, Dissertations, and Problem Reports (ETD)

Due to increased availability and power of computational resources over the past few decades, prediction and design of novel materials using computational methods has become feasible. Simulation of material systems has become vital to the further realization of novel material systems. In order to ascertain physical properties, accurate determination and identification of stable crystalline structures is necessary. Additionally, further identification of novel properties, such as magnetic moments or orbital occupation, is necessary to further realize this goal. Global search methods provide a path to accurate prediction of these properties. In this dissertation, the Firefly algorithm and minima hopping methods are …

Two-Dimensional Bloch Electrons In Electric And Magnetic Fields, Edward Aris Diaz Fajardo

Graduate Research Theses & Dissertations

Due to their extraordinary mechanical, and fascinating electronic properties, atomically flat two-dimensional materials are attractive avenues in the search for new and interesting physical phenomena. Symmetry is a powerful tool in studying the dynamics of Bloch electrons in these crystalline solids. Here, using a tight binding description, a systematic scheme is developed to derive the symmetry labels, called irreducible representations (IRs), characterizing the Bloch eigenstates in a crystal, including an extensive discussion on the possibility that these IRs are not always unique. This theory is illustrated using monolayer MoS$_2$ and few-layer graphene as examples. Using this symmetry analysis in conjunction …

Scanning Probe Microscopy Measurements On 2d Materials And Iridates, Armin Ansary

Theses and Dissertations--Physics and Astronomy

In the past two decades, there has been a quest to understand and utilize novel materials such as iridates and two-dimensional (2D) materials. These classes of materials show a lot of interesting properties both in theoretical predictions as well as experimental results. Physical properties of some of these materials have been investigated using scanning probe measurements, along with other techniques.

One-dimensional (1D) catalytic etching was investigated in few-layer hexagonal boron nitride (hBN) films. Etching of hBN was shown to share several similarities with that of graphitic films. As in graphitic films, etch tracks in hBN commenced at film edges and …

Effect Of Hydrogen Exposure On The Electronic And Optical Properties Of Insulating Titanates, John G. Connell

Theses and Dissertations--Physics and Astronomy

Hydrogen exposure of insulating d⁰-titanates, such as SrTiO₃ (STO), has displayed the formation of intriguing conducting states. These conducting states form through the use of forming gas (N₂/H₂) annealing or hydrogen plasma exposure, where hydrogen gas is exposed to high energy microwaves. The exposure of STO to hydrogen causes metallic conductivity due to the introduction of hydrogen cations on some of the oxygen sites. However, the optical properties of this hydrogen-exposed STO have not been well-studied. Further, Ba_0.5Sr_0.5TiO₃ (BST), an insulating dielectric, also shows changes in its conductivity …

Electronic Properties Of Atomically Thin Material Heterostructures, M. Javad Farrokhi

Theses and Dissertations--Physics and Astronomy

There is a movement in the electronic industry toward building electronic devices with dimensions smaller than is currently possible. Atomically thin 2D material, such as graphene, bilayer graphene, hBN and MoS2 are great candidate for this goal and they have a potential set of novel electronic properties compare to their bulk counterparts due to the exhibition of quantum confinement effects. To this goal, we have investigated the electric field screening of multilayer 2D materials due to the presence of impurity charge in the interface and vertical electric fifield from back gate. Our result shows a dramatic difference of screening behavior …

The Structure And Stability Of Cationic Metal-Benzene Clusters, Daniel P. Rabayda

Theses and Dissertations

We have investigated the size-dependent stability and structure of benzene, aluminum-benzene, and vanadium-benzene clusters. Motivated by gas-phase experimental studies performed by an experimental collaborator, we have used first-principle electronic structure methods to identify the structure of Al⁺(Bz)_n, V⁺(Bz)_n, and Bz_n clusters. Our studies reveal that cationic aluminum-benzene clusters have a magic number of 13, and that its high stability may be understood by analyzing the structure of the cluster. We also investigate the structure of vanadium-benzene clusters which have a magic number of 2. Here I examine the benzene-cation and benzene-benzene …

Electronic And Geometric Structure Of Alnom And Alnom +, Albert R. Armstrong

Theses and Dissertations

Generally, the electronic stability of aluminum clusters is associated with either closed electronic shells of delocalized electrons, or aluminum in the +3 state. To explore alternative routes for electronic stability in aluminum oxide clusters, theoretical methods were used to examine the geometric and electronic structure of Al_nO_m (2≤n≤7; 1≤m≤10) clusters. Two types of electronically stable clusters with large HOMO-LUMO gaps were identified the first being Al_2nO_3m clusters with a +3 oxidation state on the aluminum, and the second being planar clusters such as Al₄O₄, Al₅O₃, Al …

Transient Transmission Oscillations In Doped And Undoped Lithium Niobate Induced By Near-Infrared Femtosecond Pulses, Bryan J. Crossman, Gregory J. Taft

Physics Faculty Publications

Transient transmission oscillations in X-cut and Z-cut congruent, iron-doped, and magnesium-doped lithium niobate samples were measured using 50 fs, 800 nm, 0.5 nJ pulses from a self-mode-locked Ti:sapphire laser in an optical pump–probe system. Several Raman-active oscillation modes excited by these pulses were observed as changes in the transmitted probe intensity versus time delay between the pump and probe pulses. The samples were rotated to determine how the incident polarization of the pump pulses affects the mode excitations. The observed Raman-active oscillations correspond to previously reported symmetry modes measured with traditional, continuous-wave, Raman spectroscopy using the same scattering …

Boundary Twists, Instabilities, And Creation Of Skyrmions And Antiskyrmions, Aldo Raeliarijaona, Rabindra Nepal, Alexey Kovalev

Department of Physics and Astronomy: Faculty Publications

We formulate and study the general boundary conditions dictating the magnetization profile in the vicinity of an interface between magnets with dissimilar properties. Boundary twists in the vicinity of an edge due to Dzyaloshinskii-Moriya interactions have been first discussed by Wilson et al. [Phys. Rev. B 88, 214420 (2013)] and by Rohart and Thiaville [Phys. Rev. B 88, 184422 (2013)]. We show that in general case the boundary conditions lead to the magnetization profile corresponding to the Néel, Bloch, or intermediate twist. We explore how such twists can be utilized for creation of skyrmions and antiskyrmions, e.g., in a view …

Computational Prediction, Characterization, And Methodology Development For Two-Dimensional Nanostructures: Phosphorene And Phosphide Binary Compounds., Congyan Zhang

Electronic Theses and Dissertations

In this thesis, a comprehensive computational simulation was carried out for predicting, characterizing, and applications of two-dimensional (2D) materials. The newly discovered GaP and InP layers were selected as an example to demonstrate how to explore new 2D materials using computational simulations. The performance of phosphorene as the anode material of Lithium-ion battery was discussed as the example of the application of 2D material. Furthermore, the semi-empirical Hamiltonian for phosphorous and lithium elements have been developed for our future work on the application of phosphorus and lithium-based systems. The novel 2D materials of GaP and InP binary compounds were found …

Directly Photoexcited Dirac And Weyl Fermions In Zrsis And Nbas, Christopher P. Weber, Leslie M. Schoop, Stuart S. P. Parkin, Robert C. Newby, Alex Nateprov, Bettina Lotsch, Bala Murali Krishna Mariserla, J. Matthew Kim, Keshav M. Dani, Hans A. Bechtel, Ernerst Arushanov, Mazhar Ali

Physics

We report ultrafast optical measurements of the Dirac line-node semimetal ZrSiS and the Weyl semimetal NbAs, using mid-infrared pump photons from 86 meV to 500 meV to directly excite Dirac and Weyl fermions within the linearly dispersing bands. In NbAs, the photoexcited Weyl fermions initially form a non-thermal distribution, signified by a brief spike in the differential reflectivity whose sign is controlled by the relative energy of the pump and probe photons. In ZrSiS, electron-electron scattering rapidly thermalizes the electrons, and the spike is not observed. Subsequently, hot carriers in both materials cool within a few picoseconds. This cooling, as …

Physical Electronic Properties Of Self-Assembled 2d And 3d Surface Mounted Metal-Organic Frameworks, Radwan Elzein

USF Tampa Graduate Theses and Dissertations

Metal-organic frameworks stand at the frontiers of molecular electronic research because they combine desirable physical properties of organic and inorganic components. They are crystalline porous solids constructed by inorganic nodes coordinated to organic ligands to form 1D, 2D, or 3D structures. They possess unique characteristics such as ultrahigh surface area crystal lattices up to 10000 m² g^-1, and tunable nanoporous sizes ranging from 0.2 to 50 nm. Their unprecedented structural diversity and flexibility beyond solid state materials can lead to unique properties such as tailorable electronic and ionic conductivity which can serve as interesting platforms for a …

The Effects Of Pressure And Magnetic Field On Phase Transitions And Related Physical Properties In Solid State Caloric Materials, Ahmad Ikhwan Us Saleheen

LSU Doctoral Dissertations

Solid-state caloric effects, such as the magnetocaloric (MCE) and barocaloric (BCE) effects, may be utilized in future cooling technologies that are more efficient and environment-friendly. Large caloric effects often occur near phase transitions, especially near coupled first-order magnetostructural transitions (MST), and are initiated by external parameters, such as magnetic field or hydrostatic pressure. In this dissertation, the effects of pressure, temperature, and magnetic field on the phase transitions in three material systems are studied in order to elucidate how the respective caloric effects are affected.

In the first study, the realization of a coupled MST in a MnNiSi-based system through …

Genetic Algorithm Design Of Photonic Crystals For Energy-Efficient Ultrafast Laser Transmitters, Troy A. Hutchins-Delgado

Shared Knowledge Conference

Photonic crystals allow light to be controlled and manipulated such that novel photonic devices can be created. We are interested in using photonic crystals to increase the energy efficiency of our semiconductor whistle-geometry ring lasers. A photonic crystal will enable us to reduce the ring size, while maintaining confinement, thereby reducing its operating power. Photonic crystals can also exhibit slow light that will increase the interaction with the material. This will increase the gain, and therefore, lower the threshold for lasing to occur. Designing a photonic crystal for a particular application can be a challenge due to its number of …