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Articles 1 - 11 of 11
Full-Text Articles in Physical Sciences and Mathematics
Charge Effects In Bilayer Electric Transport, Christopher Czech
Charge Effects In Bilayer Electric Transport, Christopher Czech
All Theses
The mathematical isomorphism between the layer index in a bilayer system and the spin index in a spin-polarized system is used to draw an analogy between phenomena that occur in the two systems as a result of the electron-electron (e-e) interaction. First, the classical case of the Coulomb drag, a phenomenon resulting from momentum transfer through e-e collisions, is reviewed for both bilayer systems and spin-polarized systems. Then, the spin-backflow phenomenon, a result of the interaction-induced changes in the local quasiparticle energy that affects the charge transport in spin-polarized systems is presented. Finally, the iso-spin correlation is exploited to establish …
Spin Density Wave Phases In Semiconductor Superlattice, Liqiu Zheng
Spin Density Wave Phases In Semiconductor Superlattice, Liqiu Zheng
All Dissertations
We discuss the existence of spin instabilities and of possible ground states with broken spin symmetry in the presence of a tilted magnetic field for several semiconductor heterostructures. In each instance, the fundamental premise of our study is the existence of a spin degeneracy, controlled by tuning various experimentally controllable parameters, that permits the apparition of spin-flip processes driven entirely by the many-body Coulomb interaction. If in the case of a single quantum well, the spin instabilities trigger an abrupt paramagnetic to ferromagnetic phase transition, we demonstrate that in superlattices, at low temperatures, a stable spin density wave ($SDW$) ground …
The Thermoelectric Properties Investigation Of Ir3Ge7 Typed Representatives, Huqin Zhang
The Thermoelectric Properties Investigation Of Ir3Ge7 Typed Representatives, Huqin Zhang
All Theses
Energy conversion is employed to power generation utilizing the Seebeck effect or cooling utilizing the Peltier effect. Herein, we study several Ir3Ge7 typed semiconductor materials for potential thermoelectric energy conversion. Mo3Sb7, crystallizing in Ir3Ge7 type, can be rendered semiconducting by a partial Sb-Te substitution without noticeable structure changes, resulting in Mo3Sb5Te2 with 55 valence electrons per formula unit. Meanwhile, large cubic voids in the Mo3Sb5Te2 crystal structure provide the possibility of filling the voids with small cations to decrease the …
Comparison Of Thermoelectric Properties Of Arc-Melted And Hot-Pressed Half-Heuslers, Brad Edwards
Comparison Of Thermoelectric Properties Of Arc-Melted And Hot-Pressed Half-Heuslers, Brad Edwards
All Theses
Relatively low thermal conductivity and great electrical properties in combination with wide tuning parameters through doping make half-Heuslers high potential thermoelectric materials. In this study we plan to investigate the effects of hot-pressing and arc-melting on the thermoelectric properties of ZrNiSn0.975Sb0.025, and Hf0.75Zr0.25NiSn0.975Sb0.025 samples. Also, the effects of electron and phonon scattering due to the insertion of small 50 nm particles within the sample were investigated in ZrNiSn0.975Sb0.025 +4% Al2O3 and Hf0.75Zr0.25NiSn0.975Sb0.025 +4% Al2O …
Comparison Between Steady State And Laser Flash Techniques, Justine Andrews
Comparison Between Steady State And Laser Flash Techniques, Justine Andrews
All Theses
Thermoelectrics is a promising avenue of energy conservation. A material is deemed a good thermoelectric material when it portrays certain material characteristics. These characteristics include a high thermopower and electrical conductivity and a low thermal conductivity. This thesis focuses on the methods of measuring a material's thermal conductivity.
The steady state method is a measurement technique used in the low temperature thermal conductivity measurements. This technique assures that the system and sample are at equilibrium before a measurement point is taken. As a result the measurements are both precise and accurate.
The laser flash technique measures a sample's thermal conductivity …
Electronic Structure Of Mos2 Nanotubes, Lingyun Xu
Electronic Structure Of Mos2 Nanotubes, Lingyun Xu
All Dissertations
First-principles methods enable one to study the electronic structure of solids, surfaces, or clusters as accurately as possible with moderate computational effort.
So we used a first-principles electronic structure method to calculate the electronic structure of free-standing layer of MoS2 with ABA and ABC stacking. Our results suggest MoS2 with ABA stacking which appears as an insulator has an energy gap of 1.64 eV. The covalent bonds between molybdenum and sulfur atoms are strong enough to form this gap. The ABC stacking will break the symmetry and becomes metallic. The valance and impurities calculations show the rigid-band picture …
Transport Critical Currents In Ybacuo-Based Coated Conductors: Angular, Magnetic Field, And Temperature Dependencies, Samuel M. Travaglini
Transport Critical Currents In Ybacuo-Based Coated Conductors: Angular, Magnetic Field, And Temperature Dependencies, Samuel M. Travaglini
Masters Theses
High-temperature superconductivity has been a focus of much study over the past 20 years, particularly within the cuprate class of superconductors. The effectiveness of these cuprate superconductors is limited by factors including the formation of vortices within the superconductor, orientation within external magnetic fields, the strength of these magnetic fields, temperature, and whether any doping agents have been used. Any of these factors individually can affect the transport critical current levels. In this research, YBaCuO and NdBaCuO-based coated conductors were studied in a liquid-nitrogen-cooled environment at either 77 K or 65 K. Field levels were varied between 0 T and …
Raman Spectroscopic Evidence For Anharmonic Phonon Lifetimes And Blueshifts In 1d Structures, Rahul Rao
Raman Spectroscopic Evidence For Anharmonic Phonon Lifetimes And Blueshifts In 1d Structures, Rahul Rao
All Dissertations
Anharmonic effects in two different quasi-1D systems were probed via micro-Raman spectroscopy. In the first system, we observed upshifts of peaks in the Raman spectra for b-Ga2O3 nanowires grown along the [110] growth direction compared those present in bulk b-Ga2O3. Contrary to our Raman studies on -Ga2O3 nanowires, downshifts in the Raman spectrum for b-Ga2O3 nanowires grown along [401] direction has also been reported by other research groups. We attribute these Raman shifts to the growth direction-induced lattice strains (compressive and tensile) present in the nanowires, and present a model based on the quasi-harmonic density functional theory to support our …
Magneto-Optical Imaging Of Superconducting Mgb2 Thin Films, Stephanie Maria Hummert
Magneto-Optical Imaging Of Superconducting Mgb2 Thin Films, Stephanie Maria Hummert
Dissertations, Theses, and Masters Projects
No abstract provided.
Magnetization Dynamics And Anisotropy In Ferromagnetic/Antiferromagnetic Ni/Nio Bilayers, Andreas Petersen
Magnetization Dynamics And Anisotropy In Ferromagnetic/Antiferromagnetic Ni/Nio Bilayers, Andreas Petersen
Dissertations, Theses, and Masters Projects
No abstract provided.
First-Principles Calculations Of Electric Field Gradients In Complex Perovskites, Dandan Mao
First-Principles Calculations Of Electric Field Gradients In Complex Perovskites, Dandan Mao
Dissertations, Theses, and Masters Projects
Various experimental and theoretical work indicate that the local structure and chemical ordering play a crucial role in the different physical behaviors of lead-based complex ferroelectrics with the ABO 3 perovskite structure. First-principles linearized augmented plane wave (LAPW) with the local orbital extension method within local density approximation (LDA) are performed on structural models of Pb(Zr1/2Ti1/2 )O3 (PZT), Pb(Sc1/2Ta1/2)O3 (PST), Pb(Sc2/3W1/3)O3 (PSW), and Pb(Mg 1/3Nb2/3)O3 (PMN) to calculate electric field gradients (EFGs). In order to simulate these disordered alloys, various structural models were constructed with different imposed chemical orderings and symmetries. Calculations were carried out as a function of B-site …