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Full-Text Articles in Physical Sciences and Mathematics

A Systematic Study Of Transport, Magnetic And Thermal Properties Of Layered Iridates, Oleksandr B. Korneta Jan 2012

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 …


Deciphering The Arrangement Of Dust In The Clumpy Tori Of Active Galactic Nuclei, Grant David Thompson Jan 2012

Deciphering The Arrangement Of Dust In The Clumpy Tori Of Active Galactic Nuclei, Grant David Thompson

Theses and Dissertations--Physics and Astronomy

In the framework of active galactic nuclei (AGNs), a galaxy’s supermassive black hole is surrounded by a dusty torus whose clumpy configuration allows for either direct or obscured views toward the central engine. Viewing AGNs from different angles gives rise to a variety of AGN classifications; for example, the generic Type 1 AGN class requires the detection of optically broad emission lines, which arise from quickly moving material within the torus, whereas Type 2 AGNs lack these observations. While these viewing angles are not directly observable, synthetic torus models generated with CLUMPY provide a means to determine them along with …


The Development And Implementation Of Electromechanical Devices To Study The Physical Properties Of Sr2iro4 And Tas3, John A. Nichols Jan 2012

The Development And Implementation Of Electromechanical Devices To Study The Physical Properties Of Sr2iro4 And Tas3, John A. Nichols

Theses and Dissertations--Physics and Astronomy

Transition metal oxides (TMO) have proven to exhibit novel properties such as high temperature superconductivity, magnetic ordering, charge and spin density waves, metal to insulator transitions and colossal magnetoresistance. Among these are a spin-orbit coupling (SOC) induced Mott insulator Sr2IrO4. The electric transport properties of this material remain finite even at cryogenic temperatures enabling its complex electronic structure to be investigated by a scanning tunneling microscope. At T = 77 K, we observed two features which represent the Mott gap with a value of 2D ~ 615 meV. Additionally an inelastic loss feature was observed inside …


Magnetic Fields And Other Physical Conditions In The Interstellar Medium, Furea Kiuchi Jan 2012

Magnetic Fields And Other Physical Conditions In The Interstellar Medium, Furea Kiuchi

Theses and Dissertations--Physics and Astronomy

This document consists of two very different projects but the common thread is in the interest of magnetic fields. It describes the effect of magnetic fields in two Interstellar Medium regions in the Galaxy. Electromagnetic force is one of the four fundamental forces in physics. It is not known where magnetic field has initially risen in the Universe, but what is certain is that it has significant effect in the dynamics of star formation and galaxy formation. The studies aim to better understand the effects of field in an active star forming region and in the halo of the Galaxy. …


Magnetic And Orbital Orders Coupled To Negative Thermal Expansion In Mott Insulators, Ca2ru1-Xmxo4 (M = 3d Transition Metal Ion), Tongfei Qi Jan 2012

Magnetic And Orbital Orders Coupled To Negative Thermal Expansion In Mott Insulators, Ca2ru1-Xmxo4 (M = 3d Transition Metal Ion), Tongfei Qi

Theses and Dissertations--Physics and Astronomy

Ca2RuO4 is a structurally-driven Mott insulator with a metal-insulator (MI) transition at TMI = 357K, followed by a well-separated antiferromagnetic order at TN = 110 K. Slightly substituting Ru with a 3d transition metal ion M effectively shifts TMI and induces exotic magnetic behavior below TN. Moreover, M doping for Ru produces negative thermal expansion in Ca2Ru1-xMxO4 (M = Cr, Mn, Fe or Cu); the lattice volume expands on cooling with a total volume expansion ratio reaching as high as 1%. The onset of the …


Magnetic Properties Of Nb/Ni Superconducting / Ferromagnetic Multilayers, Sergiy A. Kryukov Jan 2012

Magnetic Properties Of Nb/Ni Superconducting / Ferromagnetic Multilayers, Sergiy A. Kryukov

Theses and Dissertations--Physics and Astronomy

Magnetic properties of Nb/Ni superconducting (SC) / ferromagnetic (FM) multilayers exhibit interesting properties near and below SC transition. A complex Field (H) – Temperature (T) phase boundary is observed in perpendicular and parallel orientation of ML with respect to DC field. We address the critical need to develop methods to make reliable magnetic measurements on SC thin films and ML, in spite of their extreme shape anisotropy and the strong diamagnetic response of the SC state.

Abrupt, highly reproducible “switching” of the SC state magnetization near the normal-state FM coercive fields has been observed in Nb/Ni ML. The SC penetration …


Time-Dependent Systems And Chaos In String Theory, Archisman Ghosh Jan 2012

Time-Dependent Systems And Chaos In String Theory, Archisman Ghosh

Theses and Dissertations--Physics and Astronomy

One of the phenomenal results emerging from string theory is the AdS/CFT correspondence or gauge-gravity duality: In certain cases a theory of gravity is equivalent to a "dual" gauge theory, very similar to the one describing non-gravitational interactions of fundamental subatomic particles. A difficult problem on one side can be mapped to a simpler and solvable problem on the other side using this correspondence. Thus one of the theories can be understood better using the other.

The mapping between theories of gravity and gauge theories has led to new approaches to building models of particle physics from string …


Obscuration In Active Galactic Nuclei, Robert Nikutta Jan 2012

Obscuration In Active Galactic Nuclei, Robert Nikutta

Theses and Dissertations--Physics and Astronomy

All classes of Active Galactic Nuclei (AGN) are fundamentally powered by accretion of gas onto a supermassive black hole. The process converts the potential energy of the infalling matter to X-ray and ultraviolet (UV) radiation, releasing up to several 1012 solar luminosities.

Observations show that the accreting "central engines" in AGN are surrounded by dusty matter. The dust occupies a "torus" around the AGN which is comprised of discrete clumps. If the AGN radiation is propagating through the torus on its way to an observer, it will be heavily re-processed by the dust, i.e. converted from UV to infrared …


Zeeman Effect Studies Of Magnetic Fields In The Milky Way, Kristen Lynn Thompson Jan 2012

Zeeman Effect Studies Of Magnetic Fields In The Milky Way, Kristen Lynn Thompson

Theses and Dissertations--Physics and Astronomy

The interstellar medium (ISM) of our Galaxy, and of others, is pervaded by ultra low-density gas and dust, as well as magnetic fields. Embedded magnetic fields have been known to play an important role in the structure and dynamics of the ISM. However, the ability to accurately quantify these fields has plagued astronomers for many decades. Unfortunately, the experimental techniques for measuring the strength and direction of magnetic fields are few, and they are observationally challenging. The only direct method of measuring the magnetic field is through the Zeeman effect.

The goal of this dissertation is to expand upon the …