Physics Commons^™

Pressure - Temperature Phase Diagram Of Crsite3, J L. Musfeldt, David Mandrus, Zhenxian Liu

Chemistry Publications and Other Works

van der Waals solids are well known to host remarkable phase diagrams with competing phases, unusual energy transfer processes, and elusive states of matter. Among this class of materials, chalcogenides have emerged as the most flexible and relevant platforms for unraveling charge-structure-function relationships. In order to explore the properties of complex chalcogenides under external stimuli, we measured the far infrared spectroscopic response of CrSiTe3 under extreme pressure-temperature conditions. Analysis of the 368 cm−1 Si-Te stretching mode and the manner in which it is screened by the closure of the indirect gap reveals that the insulator-metal transition takes place immediately after …

Numerical Studies Of Superconductivity And Charge-Density-Waves: Progress On The 2d Holstein Model And A Superconductor-Metal Bilayer, Philip M. Dee

Doctoral Dissertations

The problem of superconductivity has been central in many areas of condensed matter physics for over 100 years. Despite this long history, there is still no theory capable of describing both conventional and unconventional superconductors. Recent experimental observations such as the dilute superconductivity in SrTiO₃ and near room-temperature superconductivity in hydride compounds under extreme pressure have renewed interest in electron-phonon systems. Adding to this is evidence that electron-phonon coupling may play a supporting role in unconventional systems like the cuprates and monolayer FeSe on SrTiO₃.

One way to make sense of these observations is to construct simple …

Exploring Structural And Electronic Properties Of Triangular Adatom Layers On The Silicon Surface Through Adsorbate Doping, Tyler S. Smith

Doctoral Dissertations

The analysis of the electronic structure and morphology of 1/3 monolayers (ML) of Sn or Pb on Si(111) and Ge(111) has played an important role in understanding the role of electronic correlations in two dimensions. Specifically, the two-dimensional lattice of partially filled dangling bonds of these so-called α-phases has been an important testbed for studying structural phase transitions and correlated electronic phenomena ever since the discovery of a surface charge density wave in the Pb/Ge(111) system more than two decades ago. With the exception of the novel Sn/Si(111) system, all $\alpha$-phases undergo a charge ordering transition at low temperature. The …

Study Of Ferroelectric Oxides And Field Effect In Complex Oxides Heterostructures, Lu Jiang

Doctoral Dissertations

With the rapid development of technology, the need for novel materials and state-of-theart devices is growing fast. Complex oxides which have strongly correlated electrons are favorable candidates for materials industry, due to their rich phase diagrams and multiple functions. Especially, ferroelectric oxides is very promising materials in the industry for storage, due to their bistable polarization states triggered by external electrical field. This thesis is centered on ferroelectric oxides, analyzing their lattice structures and investigating the interface of ferroelectrics and other complex oxides to examine the potential of the heteostructures in the application in electronic devices.

The most notable feature …

Neutron Scattering Studies Of Cuprates And Iron Pnictides, Mengshu Liu

Doctoral Dissertations

Presented within are neutron scattering studies of several different high temperature superconducting materials: BaFe_1.9Ni_0.1As₂ [Barium Iron Nickel Arsenic], BaFe_1.85Ni_0.15As₂ [Barium Iron Nickel Arsenic], Ba_0.67K_0.33Fe₂As₂ [Barium Potassium Iron Arsenic], and Pr_0.88LaCe_0.12CuO_4-y [Praseodymium Lanthanum Cerium Copper Oxide]. The main focus is on the magnetic excitations within the systems.

For BaFe_1.9Ni_0.1As₂ [Barium Iron Nickel Arsenic], we measured the intensity of its magnetic excitations and compared the results with excitations in antiferromagnetic non-superconducting BaFe₂As_{2 …}

Condensed Matter From Gauge/Gravity Duality, Jason Edward Therrien

Doctoral Dissertations

Currently strongly coupled systems present the greatest challenge to theoretical physics. For years conventional methods of approach have failed to describe these systems analytically. In recent years it has been shown that there is a duality between weakly coupled and strongly coupled systems, the Gauge Theory/Gravity Duality. In this dissertation I will discuss how the AdS/CFT is used to describe strongly coupled condensed matter systems as well as present the work done by the author and collaborators.

Magnetic Excitations In The Iron Based Superconductors, Leland Weldon Harriger

Doctoral Dissertations

Presented within are neutron scattering studies detailing the spin dynamics of BaNi$_{x}$Fe$_{2-x}$As$_{2}$ for x = 0 (parent), 0.04 (underdoped), and 0.1 (optimal) dopings, and FeSe$_{x}$Te$_{1-x}$ for x = 0 (parent), 0.3 (underdoped), and 0.4 (optimal) dopings. These recently discovered Fe-based superconducting compounds are strikingly similar, in many respects, to the cuprate class of unconventional superconductors and share qualitatively similar phase diagrams consisting of a long range ordered magnetic ground state in the parents which, upon doping, is supplanted in favor of superconductivity. The dopings discussed herein allow us to tune through the phase diagram, beginning with long range ordered parents …

Iron Pnictides: Superconductivity In Multi-Orbital Systems, Andrew David Nicholson

Doctoral Dissertations

This work focuses on the development and implementation of microscopic models as well as their numerical and analytical study to elucidate the properties of the iron pnictides. There are many first principle and phenomenological studies of these materials, but there is a need for unbiased numerical calculations following an approach similar to the one used in the study of the Hubbard and t-J models for the cuprates.

First a two orbital model for the pnictides, focusing on two hybridized Fe-d orbitals (dxz and dyz) is formulated, including hoppings between nearest and next nearest neighbors as well as on site Coulomb …

Superconducting Nafe1-Xcoxas: Crystal Growth, Resistivity, And Susceptibility Measurements, Tucker Netherton

Chancellor’s Honors Program Projects

No abstract provided.

An Investigation Of Pinning Landscapes With Engineered Defects: Contact-Free Critical Current Density Measurements, John William Sinclair

Doctoral Dissertations

Pinning landscapes in modern second generation coated conductors are excellent candidates for studies of vortex pinning. The ability to produce engineered defects in thin films of high temperature superconductors allows one to investigate representative distinct pinning sites, with the objective of understanding how different pinning centers contribute, compete and evolve under varying conditions of magnetic field strength and orientation, and temperature.New contact-free methods were developed specifically to investigate this system in new ways, especially the dependence of the critical current density Jc on orientation of the magnetic field. A superconducting quantum interference device (SQUID)-based magnetometer was used to determine angular …

Interplay Between Structure And Chemistry Of Materials And Their Physical Properties, Alaska Subedi

Doctoral Dissertations

First principles calculations provide a powerful tool for sorting out the interplay of chemical composition and structure with the physical properties of materials. In this dissertation, I discuss the physical properties and their microscopic basis within this framework for following illustrative examples. (i) The Zintl phase hydrides, where I find H is anionic and the formation of covalent sp2 bonds in the Al/Ga/Al-Si planes, which is a highly unusual bonding configuration for these elements. (ii) PbTe, which shows strong coupling between the longitudinal acoustic and transverse optic modes that may explain its low thermal conductivity. (iii) The double perovskites BiPbZnNbO6 …