Condensed Matter Physics Commons^™

Magnetic Properties And Defects In Iron Implanted Strontium Titanate Single Crystals And Thin Films, Misha Chavarha

Electronic Thesis and Dissertation Repository

Physical vapor deposition was used to grow good quality crystalline stoichiometric SrTiO₃ thin films on Si(001) substrate using a systematic approach starting from understanding of kinetics and thermodynamics of the system and finishing with the development of procedure for high quality SrTiO₃/Si interface. Growth of optimized SrTiO₃ perovskite structure on Si requires careful transformation of a thin interfacial SrSix layer into the initial SrTiO₃ lattice cells. The critical aspects of the growth, such as low temperature and low oxidant partial pressure, are explained in details. Crystallinity and stoichiometry of SrTiO₃ were verified using powder …

Temperature-Sensitive Chemical Cell Based On Nickel (Ii) Phthalocyanine-Tetrasulfonic Acid Tetrasodium Salt, Shahino Mah Abdullah

Shahino Mah Abdullah

An organic compound Nickel (II) phthalocyanine-tetrasulfonic acid tetrasodium salt (NiTSPc) has been studied as a potential material for a solution based temperature sensor. Using NiTSPc, an ITO/NiTSPc solution/ITO chemical cell has been made and characterized in the temperature range of 20–85 ◦C. This sensor works on the principle of change in the resistance and capacitance of the chemical cell caused by the temperature variation. Good response/recovery and small hysteresis have been attained. The proposed sensor is aimed to evolve towards highly sensitive organic temperature sensor in a specific temperature range.

Microwave Optics Research, Allen Andersen, Todd Lines, Josh Barney

Allen Andersen

The BYU-Idaho Physics Department x-band microwave optics equipment was originally intended for use in classroom demonstrations. I evaluated this equipment for use in research. I designed and built additional equipment needed in order to perform attenuation and other experiments then used it to conduct research on the transmission properties of paper and other substances. The new equipment allowed me to create a standard experimental procedure, take reasonably accurate measurements, and reduce undesired standing wave effects. Mathematical and experimental analysis was done to determine the necessary parameters of the new equipment. The new apparatus is comparable to setups featured in published …

Multidimensional Spectroscopy Of Semiconductor Quantum Dots, Jason Michael Bylsma

USF Tampa Graduate Theses and Dissertations

The coherent properties of semiconductor nanostructures are inherently difficult to measure and one-dimensional spectroscopies are often unable to separate inhomogeneous and homogeneous linewidths. We have refined and improved a method of performing multidimensional Fourier transform spectroscopy based on four-wave

mixing (FWM) experiments in the box geometry. We have modified our system with broadband beamsplitters in all interferometer arms, high-resolution translation stages and the ability to work in reflection geometry. By improving the phase-stability of our setup and scanning pulse delays with sub-optical cycle precision, we are able to

reproduce 2DFT spectra of GaAs multiple quantum wells. With the FWM signal …

Demonstration Of The Gunnarsson-Lundqvist Theorem And The Multiplicity Of Potentials For Excited States, Yu-Qi Li, Xiao-Yin Pan, Biao Li, Viraht Sahni

Publications and Research

The Gunnarsson-Lundqvist (GL) theorem of density functional theory states that there is a one-to-one relationship between the density of the lowest nondegenerate excited state of a given symmetry and the external potential. As a consequence, knowledge of this excited state density determines the external potential uniquely. [The GL theorem is the equivalent for such excited states of theHohenberg-Kohn (HK) theorem for nondegenerate ground states.] For other excited states, there is no equivalent of the GL or HK theorem. For these states, there thus exist multiple potentials that generate the excited-state density. We show, by example, the satisfaction that the GL …

Electron Drift-Mobility Measurements In Polycrystalline Cuin1-Xgaxse2 Solar Cells, Steluta A. Dinca, Eric A. Schiff, William N. Shafarman, Brian Egaas, Rommel Noufi, David L. Young

Physics - All Scholarship

We report photocarrier time-of-flight measurements of electron drift mobilities for the p-type CuIn_1-xGa_xSe₂ films incorporated in solar cells. The electron mobilities range from 0.02 to 0.05 cm^2/Vs and are weakly temperature-dependent from 100–300 K. These values are lower than the range of electron Hall mobilities (2-1100 cm²/Vs) reported for n-type polycrystalline thin films and single crystals. We propose that the electron drift mobilities are properties of disorder-induced mobility edges and discuss how this disorder could increase cell efficiencies.

Robust Isothermal Electric Control Of Exchange Bias At Room Temperature, Xi He, Yi Wang, Christian Binek, Peter Dowben

Christian Binek

Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with highspeed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive …

Capillary Force In High Aspect-Ratio Micropillar Arrays, Dinesh Chandra

Dinesh Chandra

High aspect-ratio (HAR) micropillar arrays are important for many applications including, mechanical sensors and actuators, tunable wetting surfaces and substrates for living cell studies. However, due to their mechanical compliance and large surface area, the micropillars are susceptible to deformation due to surface forces, such as adhesive force and capillary force. In this thesis we have explored the capillary force driven mechanical instability of HAR micropillar arrays. We have shown that when a liquid is evaporated off the micropillar arrays, the pillars bend and cluster together due to a much smaller capillary meniscus interaction force while still surrounded by a …

Ferroelectric And Multiferroic Tunnel Junctions, Evgeny Y. Tsymbal, Alexei Gruverman, Vincent Garcia, Manuel Bibes, A. Barthélémy

Evgeny Tsymbal Publications

The phenomenon of electron tunneling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fi elds of physics, as well as creating sub-fi elds on its own. Spin-dependent tunneling in magnetic tunnel junctions has aroused considerable interest and development. In parallel with this endeavor, recent advances in thin-fi lm ferroelectrics have demonstrated the possibility of achieving stable and switchable ferroelectric polarization in nanometer-thick fi lms. This discovery opened the possibility of using thin-fi lm ferroelectrics as barriers in magnetic tunnel junctions, thus merging the fi elds of magnetism, ferroelectricity, and spin-polarized transport …

Majorana Modes In Time-Reversal Invariant S -Wave Topological Superconductors, Shusa Deng, Lorenza Viola, Gerardo Ortiz

Dartmouth Scholarship

We present a time-reversal invariant s-wave superconductor supporting Majorana edge modes. The multiband character of the model together with spin-orbit coupling are key to realizing such a topological superconductor. We characterize the topological phase diagram by using a partial Chern number sum, and show that the latter is physically related to the parity of the fermion number of the time-reversal invariant modes. By taking the self-consistency constraint on the s-wave pairing gap into account, we also establish the possibility of a direct topological superconductor-to-topological insulator quantum phase transition.

Magnetoelectric Interactions Between An Organic Ferroelectric And A Transition Metal Ferromagnet, Abhijit Mardana

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

The interaction between ferromagnetic and ferroelectric films, the magnetoelectric effect, is a fascinating fundamental research area as well as having potential applications in magnetic data storage devices. We have investigated magnetoelectric coupling effects in thin film heterostructures, consists of metallic ferromagnet, cobalt, and the polymer ferroelectric [P(VDF-TrFE) 70:30]. The work described here encompasses changes in ferroelectric polarization with magnetic field as well as changes in the magnetic anisotropy with ferroelectric polarization.

In samples of Co overlayers on P(VDF-TrFE), in which the Co is not constrained by the substrate, the polarization shows a large change on application of a perpendicular magnetic …

Qpced2.0: A Computer Program For The Processing And Quantification Of Polycrystalline Electron Diffraction Patterns, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

The processing and quantification of electron diffraction patterns have become vital in advanced electron crystallographic analysis work. A computer program, QPCED2.0, has been developed for the handling of selected-area electron diffraction patterns for polycrystalline materials. QPCED2.0 can be used to enhance the visibility of electron diffraction patterns, to convert electron diffraction patterns into intensity profiles, and to retrieve precisely the lattice d spacings and the integral intensities of the diffraction rings. The design and implementation of QPCED2.0 are elucidated and application examples are given.

Assessing The Feasibility Of Cosmic-Ray Acceleration By Magnetic Turbulence At The Magnetic Center, M. Fatuzzo, F. Melia

Faculty Scholarship

No abstract provided.

Quantitative Study Of Spin-Flip Co-Tunneling Transport In A Quantum Dot, S. Herbert, T-M. Liu, A. N. Ngo

Faculty Scholarship

No abstract provided.

Optically Trapped Fluorescent Nanodiamonds, Viva Horowitz

Scholarly Projects

The nitrogen-vacancy (NV) color center in diamond is gaining significant interest for applications in nanoscale sensing. The optical addressability of the magnetically sensitive spin states and the ability to coherently control these states at room temperature makes this system an exciting candidate for spin-based magnetometry. I constructed an optical tweezers apparatus combined with a confocal fluorescence apparatus. Using the optical apparatus, we demonstrate three-dimensional position control of nanodiamonds in solution with simultaneous readout of ground-state electron-spin resonance (ESR) transitions in an ensemble of diamond nitrogen-vacancy (NV) color centers. Despite the motion and random orientation of NV centers suspended in the …

A Systematic Study Of Transport, Magnetic And Thermal Properties Of Layered Iridates, Oleksandr B. Korneta

Theses and Dissertations--Physics and Astronomy

A unique feature of the 5d-iridates is that the spin-orbit interaction (SOI) and Coulomb interactions U are of comparable strength and therefore compete vigorously. The relative strength of these interactions stabilizes new exotic ground states that provide a fertile ground for studying new physics. SOI is proportional to Z^4 (Z is the atomic number), and it is now recognized that strong SOI can drive novel narrow-gap insulating states in heavy transition metal oxides such as iridates. Indeed, strong SOI necessarily introduces strong lattice degrees of freedom that become critical to new physics in the iridates. This dissertation thoroughly examines a …

Intrinsic Defects In Multiferroic Bifeo3 And Their Effect On Magnetism, Tula R. Paudel, Sitaram S. Jaswal, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

We investigate the energetics of the intrinsic defects in bulk multiferroic BiFeO₃ and explore their implication for magnetization using a first-principles approach based on density functional theory. We find that the dominant defects in oxidizing (oxygen-rich) conditions are Bi and Fe vacancies and in reducing (oxygen-poor) conditions are O and Bi vacancies. The calculated carrier concentration shows that the BiFeO₃ grown in oxidizing conditions has p-type conductivity. The conductivity decreases with oxygen partial pressure, and the material becomes insulating with a tendency for n-type conductivity. We find that the Bi and Fe vacancies produce a magnetic …

Magnetic And Superconducting Phases At The Laalo3/Srtio3 Interface: The Role Of Interfacial Ti 3D Electrons, N. Pavlenko, Thilo Kopp, Evgeny Y. Tsymbal, George A. Sawatzky, Jochen Mannhart

Evgeny Tsymbal Publications

Ferromagnetism and superconductivity are, in most cases, adverse. However, recent experiments reveal that they coexist at interfaces of LaAlO₃ and SrTiO₃. We analyze the magnetic state within density functional theory and provide evidence that magnetism is not an intrinsic property of the two-dimensional electron liquid at the interface. We demonstrate that the robust ferromagnetic state is induced by the oxygen vacancies in SrTiO₃ or in the LaAlO₃ layer. This allows for the notion that areas with increased density of oxygen vacancies produce ferromagnetic puddles and account for the previous observation of a superparamagnetic behavior in …

Raman Spectroscopy And Diffuse Reflectance Spectroscopy For Diagnosis Of Human Cancer And Acanthosis Nigricans, Suneetha Devpura

Wayne State University Dissertations

Cancer and diabetes are common chronic diseases in today's world causing numerous deaths in adults as well as children. Most common types of cancers in adults include prostate, lung, breast, colorectal and head and neck squamous cell carcinoma, while among children; leukemia, and brain and central nervous system cancers are quite common. In each of these cases, early detection of the cancer or disease dramatically increases the chances of successful treatment. In recent years, there has been much interest in using Raman spectroscopy and diffuse reflectance spectroscopy as analytical optical spectroscopic methods for early diagnosis of diseases. Raman spectroscopy can …

Essentials Of The Theory Of Abstraction - Lecture, Subhajit Kumar Ganguly

Subhajit Kumar Ganguly

In not favouring solutions or sets of solutions, the principle of zero-postulation drives away any unwanted incompleteness from the description of the world. It is the interactions between the possible exhaustive set of solutions that creates the impression pointedness or directiveness in the universe, leading to the formation of clusters, as discussed earlier. These interactions may be chaotic in nature, giving rise to attractor points where the directiveness inside any given system asymptotically seem to approach. It is this directiveness, in turn, inside a given system or in the universe as a whole, that is the cause of all known …