Condensed Matter Physics Commons^™

Strain Engineering Of Excitonic And Vibrational Properties In Two-Dimensional Transition Metal Dichalcogenides, Sneha Minesh Patel

Graduate Theses and Dissertations

Mechanical strain represents a robust and non-invasive method for tuning the electronic and vibrational properties of two-dimensional transition-metal dichalcogenides (TMDs). This work examines homogeneous biaxial strain as a symmetry-preserving control parameter that governs excitonic and interlayer dynamics in atomically thin TMDs. In monolayer MoSe2, biaxial tensile strain is intrinsically generated during high-temperature physical vapor deposition due to thermal expansion mismatch with amorphous substrates. Optical spectroscopy demonstrates substantial and tunable excitonic energy shifts exceeding 100 meV per percent strain. Polarization-resolved second harmonic generation confirms the retention of lattice symmetry under biaxial deformation. The investigation is further extended to bilayer MoS2, where …

Structural Relaxation In Glass-Forming Liquids At Extreme Pressure: Photon-Correlation Spectroscopy And Constrained Thermodynamic Surface Modeling, Kevin Wayne Lyon

Graduate Theses and Dissertations

Structural relaxation in glass-forming liquids is strongly dependent on both temperature and pressure, yet direct measurement of structural α-relaxation under multi-gigapascal compression has remained experimentally challenging. This work extends depolarized photon correlation spectroscopy (DPCS) to pressures approaching 5 GPa in a diamond anvil cell, representing the highest-pressure implementation of this technique and enabling direct measurement of the structural α-relaxation in a pure liquid at extreme compression. This capability provides access to dynamical regimes previously unexplored by photon correlation spectroscopy and establishes a platform for probing glassy dynamics at high pressure. To describe these measurements, a constrained relaxation-time surface framework is …

A Theoretical Investigation Of Photo-Induced Deformations And Transitions In Nanoscale Ferroelectrics, Carmel Dansou

Graduate Theses and Dissertations

This dissertation presents a comprehensive first-principles investigation into the interaction of light with ferroelectric materials, focusing on light-induced structural responses (photostriction) and phase transitions in Ferroelectric superlattices, epitaxially strained BiFeO3 thin films, and twodimensional NbOX2 (X = Cl, Br, I) ferroelectrics. The work aims to provide microscopic insights into how light can control the lattice structure and even the crystallographic phase in these systems, with the broader goal of informing the design of light-responsive functional materials for practical technological applications. The first part explores light-induced effects in PbTiO3/SrTiO3 superlattices with different polarization orientations. Our simulations reveal that photoexcitation modifies the …

Ab Initio Studies On Mechanical Properties Of Freestanding Ferroic Monolayers, John Malcolm Davis

Graduate Theses and Dissertations

This thesis explores the role of mechanical properties and elastic couplings in freestanding paradigmatic ferroic monolayers within the framework of density functional theory. This dissertation is comprised of three interconnected published studies: (i) establishing the elastic behavior across a temperature-driven phase transition in SnSe monolayers; (ii) thermally-driven phase transitions in graphene-like silicene, germanene, and stanene, examining the structural stability and band gap occlusion; and (iii) magnetoelastic coupling in an Ising-like CrSiTe3 monolayer, focused on assessing magnetic contributions to the material stiffness by establishing a proper non-magnetic reference.

Synthesis And Properties Study Of Layered Magnetic Topological Materials, Gokul Acharya

Graduate Theses and Dissertations

The discovery of topological materials (TMs) has opened up exciting opportunities for probing fundamental physics and enhancing innovative device integrations. These materials display various exotic properties, such as large magnetoresistance, high mobility, chiral anomaly, and surface Fermi arcs. The magnetic versions of ZrSiS family, LnSbTe and LnPS (Ln = lanthanide) have attracted intensive attention as these materials provide a new platform to study interplay between magnetism, topological states, and electron correlations. The vast pool of topological materials has provided exciting avenues to precisely engineer the topological states by modulating spin-orbital coupling, electronic dimensionality, and lattice constant through element substitutions. This …

Tuning Electronic Transport And Magnetic Properties Of Layered Magnetic Materials, Md Rafique Un Nabi

Graduate Theses and Dissertations

Two-dimensional magnetic materials (2DMMs) have gained significant interest due to their potential for novel physical phenomena and device applications. Mn_2-xZn_xSb, with its tunable magnetic properties and stable tetragonal layered structure, offers a rich platform for exploring these phenomena. The introduction of Zn into the Mn₂Sb lattice efficiently tunes magnetic and electronic properties, making it a compelling candidate for high-performance spintronic devices.

With this motivation, we synthesized Mn_2-xZn_xSb (0 ≤ x ≤ 1) single crystals using a flux method. Mn2Sb exhibits ferrimagnetic order below 550 K with antiparallel spins aligned along …

Investigate The Importance Of Local Magnetic Moment And Magnetic Interaction In Superconducting Fese Monolayer Using Density Functional Calculations, Sudip Pokharel

Graduate Theses and Dissertations

In this dissertation, we present two projects to study superconducting FeSe monolayer using first-principles density functional calculations. Monolayer FeSe/SrTiO₃ system has very different properties as compared to its bulk counterpart in terms of critical superconducting temperature, Fermi surface topology and antiferromagnetic (AFM) stability. For FeSe monolayer, local magnetic moment (LMM) and AFM fluctuation are closely linked to superconductivity. However, LMM is not studied enough for FeSe monolayer. For FeSe/SrTiO₃ system, the substrate SrTiO₃ constrains the in-plane lattice constant for FeSe and also plays a crucial role in the onset and enhancement of superconductivity by providing charge transfer. …

Exploring Ferroelectric Phenomena In Batio3, Linbo3, And Liznsb: From Extended Oxygen Vacancies To Tri-Stable Polarization And Giant Hyperferroelectricity, Shaohui Qiu

Graduate Theses and Dissertations

This dissertation presents three projects that investigate the complex phenomena of ferroelectricity under different conditions in BaTiO3, LiNbO3, and LiZnSb using first-principles density functional calculations. Extended defects in ferroelectric solids play a crucial role in reducing the lifetime and performance of ferroelectric devices by causing fatigue, domain pinning, and aging. Thus, understanding their impact is of critical importance for the development of reliable and high-performance ferroelectric devices. In addition, hyperferroelectricity is an intriguing phenomenon that has attracted much attention in recent years. Despite the existence of depolarization field, spontaneous polarization persists under an open-circuit boundary condition (OCBC), making hyperferroelectric materials …

Understanding And Tuning Magnetism In Van Der Waals Magnetic Compounds, Rabindra Basnet

Graduate Theses and Dissertations

The recently discovered two-dimensional (2D) magnetism has attracted intensive attention due to possible magnetic phenomenon arising from 2D magnetism and their promising potential for spintronics applications. The advances in 2D magnetism have motivated the study of layered magnetic materials, and further enhanced our ability to tune their magnetic properties. Among various layered magnets, tunable magnetism has been widely investigated in metal thiophosphates MPX3. It is a class of magnetic van der Waals (vdW) materials with antiferromagnetic ordering persisting down to atomically thin limit. Their magnetism originates from the localized moments due to 3d electrons in transition metal ions. So, their …

Quantum Transport And Electric-Field Effects In Layered Topological Semimetals And Magnetic Materials, Arash Fereidouni Ghaleh Minab

Graduate Theses and Dissertations

This dissertation describes transport experiments on quantum devices in layered Dirac nodal line topological semimetals and antiferromagnetic materials down to a few layers. We used gate-induced effects to alter the transport properties of these materials.

First, we introduced current annealing in topological semimetals to achieve high-quality devices. We demonstrate current annealing to substantially improve the electronic transport properties of 2D topological semimetal flakes. Contact resistance and resistivity were improved by factors up to 2,000,000 and 20,000, respectively, in devices based on exfoliated flakes of two topological semimetals, ZrSiSe and BaMnSb2. Using this method, carrier mobility in ZrSiSe improved by a …

Study Of Thermoelectric And Lattice Dynamics Properties Of 2d Layered Mx (M = Sn, Pb; X = S, Se, Te) And Zrs2 Compounds Using First-Principles Approach, Abhiyan Pandit

Graduate Theses and Dissertations

The aim of this dissertation is the investigation of thermoelectric and lattice dynamics properties of two-dimensional (2D) MX (M = Sn, Pb; X = S, Se, Te) and ZrS2 compounds based on the first-principles density functional theory. The dimensionality reduction (e.g., using 2D structure) of bulk materials is found to have enhanced thermoelectric efficiency. This enhancement is attributed to the increase of the Seebeck coefficient as a result of higher electronic density of states near the Fermi level in low-dimensional materials. In addition, lowering the dimensionality increases phonon scattering near interfaces and surfaces in 2D materials, which leads to a …

Crystal Growth And Property Tuning Of Layered Magnetic Topological Semimetals, Krishna Pandey

Graduate Theses and Dissertations

The demand for energy-efficient devices has been growing rapidly due to the need for data-driven technologies and the global energy crisis. As device size approaches the atomic scale, the miniaturization of electronic devices may stop in the near future unless fundamentally new materials or device concepts are developed. The emergent topological materials with exotic properties show remarkable robustness against crystal lattice defects, which are promising for next-generation technology. These materials host exotic properties such as high mobility, large magnetoresistance, chiral anomaly, and surface Fermi arcs, etc. Among various topological materials, the ZrSiS-family materials exhibit two types of Dirac states, which …

Ab Initio Studies Of Structure And Properties Of Group-Iv Monochalcogenide Monolayers, Shiva Prasad Poudel

Graduate Theses and Dissertations

The goal of this dissertation is to study the structure of ferroelectric group-IV monochalcogenide monolayers (MMLs) and their material properties. This work also established a new buckled honeycomb phase of these monolayers. Chapter 1 serves as an introduction where the motivation for these studies is established. In chapter 2, I used eight different exchange-correlation functionals (XC) to study the structure of these 2D ferroelectrics and found that their properties are independent of the choice of XC functionals. These findings reveal that the ground-state ferroelectric unit cell can be described by only five independent parameters, whereas their paraelectric (square or rectangular) …

Interplay Between The Lattice And Spin Degrees Of Freedom In Magnetoelectric And Magnetic Materials, Temuujin Bayaraa

Graduate Theses and Dissertations

This dissertation contains several investigations on the cross-coupling between structural and spin degrees of freedom in multiferroic and ferrimagnetic compounds by means of first-principles calculations and ab-initio-based Monte-Carlo simulations. We start with the reviews of magnetoelectricity, ferrimagnetism, strain engineering, followed by a brief introduction to first-principles computational methods, magnetic effective Hamiltonians, and other techniques that are utilized here. The results section of the dissertation can be divided into two parts. The first half focuses on magnetoelectric effects arising from different sources, while the second half is about the ferrimagnetic nature of materials. In the first part, we examine the epitaxial …

Theoretical Investigations Of The Structural, Dynamical, Electronic, Magnetic, And Thermoelectric Properties Of Corhysi (Y = Cr, Mn) Quaternary Heusler Alloys, Abdullah Hussain Hzzazi

Graduate Theses and Dissertations

Thermoelectric materials have potential properties for utilizing waste heat. The computations are used to estimate the electronic structure of CoRhYSi (Y = Cr, Mn) Quaternary Heusler alloys, as well as their elastic and magnetic characteristics. The full-potential linearized augmented plane wave is used in the calculations. The exchange-correlations are addressed using Perdew–Burke and Ernzerhof's generalized gradient approximation (GGA-PBE). With the exception of CoRhCrSi and CoRhMnSi, which are simple ferromagnets that are approximately half metallic in nature, electronic structure calculations demonstrate that these compounds have a gap in the minority states band and are obviously half-metallic ferromagnets. The magnetic moments of …

Gaas Growth On Sapphire Substrates (C And R Plane) For Integrated Microwave Photonics (Imwp), Samir Kumar Saha

Graduate Theses and Dissertations

The microwave signal processing in the optical domain creates new opportunities for information and communication technology (ICT) and networks by increasing speed, bandwidth, and processing capability. IMWP incorporates the functions of microwave photonics components/subsystems in monolithic or hybrid photonic circuits to meet future needs. Sapphire platforms have the potential to integrate all-in-one, for instance, light source, analog signal processing, light detection, CMOS control circuit, silicon on sapphire to achieve high-performance, low-cost mixed-signal optical links etc. Molecular beam epitaxy (MBE) has been used to grow GaAs on sapphire substrates to integrate optoelectronic devices in the same platform.

The initial stage of …

Two-Dimensional Black Phosphorus For Terahertz Emission And Near-Field Radiative Heat Transfer, Mahmudul Hasan Doha

Graduate Theses and Dissertations

The main focus of this work is to investigate two potential optical and optoelectronic applications of black phosphorus (BP): the near-field radiative heat transfer in plasmonic heterostructures with graphene and terahertz emission from multi-layer BP photoconductive antennas. When the separation distance between graphene-black phosphorene is much smaller than or comparable to the thermal wavelength at different temperatures, a near-field radiation heat transfer breaks the Planck blackbody limit. The magnitude of the near-field radiation enhancement acutely depends on the gate voltage, doping, and vacuum gap of the graphene and BP pair. The strong near-field radiation heat transfer enhancement of the specific …

Structural And Electronic Properties Of Few-Layer Monochalcogenides, Brandon Joel Miller

Graduate Theses and Dissertations

This work discusses a new class of materials with novel properties that have only recently begun being studied. These materials are two-dimensional group IV-VI monochalcogenides, so named because they are formed from group IV (carbon group) and group VI (chalcogens) elements. These materials display several interesting physical properties such as ferroelasticity and ferroelectricity, and the contents within Chapters Two, Three, and Four concern a collaborative effort between theory and experiment between our group at the University of Arkansas and Dr. Kai Chang at the Max Planck Institute of Microstructure Physics in Halle, Germany in studying these properties. This thesis is …

Study Of Static And Dynamical Properties Of Complex Antiferroelectrics Materials, Kinnary Yogeshbhai Patel

Graduate Theses and Dissertations

The aim of this dissertation is the investigation of the static and dynamical properties of the complex antiferroelectric materials using Effective Hamiltonian method and First principles calculations. In chapter 3, a novel elemental interatomic coupling in perovskite materials which bilinearly couples the antiferroelectric displacements of cations with the rotations of the oxygen octahedra. This new coupling explains a very complex crystal structure of prototypical antiferroelectric PbZrO3. My explanation provides a unified description of many other complex antipolar crystal structures in variety of perovskite materials, including the occurrence of incommensurate phases in some of them. In chapter 4, results and analysis …

Stability Of Group Four Monochalcogenides In Water And Air, William Shattuck

Graduate Theses and Dissertations

Previously published works have simulated the behavior of monolayer group IV monochalcogenides and predicted them to have very useful electronic properties. These simulations have also predicted that monolayers of group IV monochalcogenides will degrade quickly when exposed to water, even in extremely low concentrations. We hypothesize that thin samples of these materials will show signs of degradation if left in air and in water for an extended period of time.

Samples of each of the four monochalcogenides (GeS, GeSe, SnS and SnSe) were exfoliated onto clean oxidized silicon substrates. Chemical analysis showed the SnSe samples were contaminated, so they were …

Static And Dynamical Properties Of Multiferroics, Sayed Omid Sayedaghaee

Graduate Theses and Dissertations

Since the silicon industrial revolution in the 1950s, a lot of effort was dedicated to the research and development activities focused on material and solid-state sciences. As a result, several cutting-edge technologies are emerging including the applications of functional materials in the design and enhancement of novel devices such as sensors, highly capable data storage media, actuators, transducers, and several other types of electronic tools. In the last two decades, a class of functional materials known as multiferroics has captured significant attention because of providing a huge potential for new designs due to possessing multiple ferroic order parameters at the …

Theoretical Investigations Of The Electronic, Magnetic, And Thermoelectric Properties Of Transition-Metal Based Compounds, Haleoot Edaan Raad

Graduate Theses and Dissertations

The electronic, magnetic, and thermoelectric properties of transition-metal based compounds were investigated by using the density functional theory and Boltzmann transport formalism. It was found that the Co-based Heusler compounds and InSe monochalcogenide are among the materials that may be used for future thermoelectric devices. Furthermore, the investigation showed that the quaternary Heusler compounds, such as, CoFeYGe, where Y is Ti or Cr, are half-metallic ferromagnetic materials with full electron spin polarization. The lattice thermal conductivity (κL) was found to decrease for these alloys as the temperature increases. The present investigation indicated that the phonon optical modes have a major …

Studies Of Initial Growth Of Gan On Inn, Alaa Alnami

Graduate Theses and Dissertations

III-nitride materials have recently attracted much attention for applications in both the microelectronics and optoelectronics. For optoelectronic devices, III-nitride materials with tunable energy band gaps can be used as the active region of devices to enhance the absorption or emission. A such material is indium nitride (InN), which along with gallium nitride (GaN) and aluminum nitride (AlN) embody the very real promise of forming the basis of a broad spectrum, a high efficiency solar cell. One of the remaining complications in incorporating InN into a solar cell design is the effects of the high temperature growth of the GaN crystal …

Properties Of Epitaxial Sr0.5ba0.5mno3 Films From First-Principles, Temuujin Bayaraa

Graduate Theses and Dissertations

Magnetoelectric multiferroics, that possess coupled magnetic and electric degrees of freedom, have been receiving ever renewed attention for more than 15 years since they hold promise for the design of novel devices exploiting their cross-coupling.

In this thesis, we present the results of first-principles studies on physical properties of multiferroic Sr0.5Ba0.5MnO3 films under epitaxial compressive and tensile strains, and chemical ordering. We start by reviewing multiferroic materials, a magnetoelectric coupling mechanism and then we give a brief introduction to the first-principles computational methods that are involved in this study.

Here, we report that Sr0.5Ba0.5MnO3 (SBM) films under compressive strain become …

A Numerical Study Of The Interaction Between One Dimensional Carbyne Chain And Single Stranded Dna, Zeina Salman

Graduate Theses and Dissertations

resolution at the single nucleotide level when developing DNA sequencers. The purpose of this research was to numerically study the electrical properties associated with the interaction between 1D carbon chain, known as carbyne, and ssDNA. First, the electrical properties of the carbyne chain were calculated. Second, the electrical properties of the carbyne chain were calculated in the presence of different ssDNA bases. Analyzing the differences between the two cases led to determining the effects of these different bases on the electrical properties. The numerical simulation approach conducted in this research was based on the first-principle simulation. The first-principle simulation was …

Artificial Quantum Many-Body States In Complex Oxide Heterostructures At Two-Dimensional Limit, Xiaoran Liu

Graduate Theses and Dissertations

As the representative family of complex oxides, transition metal oxides, where the lattice,

charge, orbital and spin degrees of freedom are tightly coupled, have been at the forefront

of condensed matter physics for decades. With the advancement of state-of-the-art heteroepitaxial deposition techniques, it has been recognized that combining these oxides on the atomic scale, the interfacial region offers great opportunities to discover emergent phenomena and tune materials' functionality. However, there still lacks general guiding principles for experimentalists, following which one can design and fabricate artificial systems on demand. The main theme of this dissertation is to devise and propose some …

Static And Dynamical Properties Of Ferroelectrics And Related Material In Bulk And Nanostructure Forms, Zhigang Gui

Graduate Theses and Dissertations

Ferroelectrics (FE) and multiferroics (MFE) have attracted a lot of attentions due to their rich and novel properties. Studies towards FE and MFE are of both fundamental and technological importance. We use a first-principles-based effective Hamiltonian method, conventional ab-initio packages and linear-scale three-dimension fragment method to investigate several important issues about FE and MFE. Tuning the properties of FE and MFE films are essential for miniaturized device applications, which can be realized through epitaxial strain and growth direction. In this dissertation, we use the effective Hamiltonian method to study (i) BaTiO 3 films grown along the (110) pseudocubic direction on …

The Effects Of Strain And Vacancies On The Electric And Vibrational Properties Of Ferroelectric Batio3 From First-Principles, Aldo Serge Michael Raeliarijaona

Graduate Theses and Dissertations

The studies of ferroelectricity (FE) are of technological significance because of the multitude of applicable properties that ferroelectric materials exhibit. The mastery, and control of these properties necessitate the knowledge of the fundamental physics governing these insulating materials.

In this dissertation I present the results of first-principles investigations of the behavior of the fundamental ferroelectric properties under strain, and in the presence of vacancies. In the first part I introduce the important FE properties, their common behavior, and their numerous valuable applications. Following this background on FEs, a review of theoretical methods is presented with topics such as: Density Functional …

Engineering The Ground State Of Complex Oxides, Derek Joseph Meyers

Graduate Theses and Dissertations

Transition metal oxides featuring strong electron-electron interactions have been at the forefront of condensed matter physics research in the past few decades due to the myriad of novel and exciting phases derived from their competing interactions. Beyond their numerous intriguing properties displayed in the bulk they have also shown to be quite susceptible to externally applied perturbation in various forms. The dominant theme of this work is the exploration of three emerging methods for engineering the ground states of these materials to access both their applicability and their deficiencies.

The first of the three methods involves a relatively new set …

Mirror Buckling Transitions In Freestanding Graphene Membranes Induced Through Scanning Tunneling Microscopy, James Kevin Schoelz

Graduate Theses and Dissertations

Graphene has the ability to provide for a technological revolution. First isolated and characterized in 2004, this material shows promise in the field of flexible electronics. The electronic properties of graphene can be tuned by controlling the shape of the membrane. Of particular interest in this endeavor are the thermal ripples in graphene membranes. Years of theoretical work by such luminaries as Lev Landau, Rudolf Peierls, David Mermin and Herbert Wagner have established that 2D crystals should not be thermodynamically stable. Experimental research on thin films has supported this finding. Yet graphene exists, and freestanding graphene films have been grown …