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Condensed matter physics

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Full-Text Articles in Physics

Gapless Symmetry-Protected Topological Order, Thomas Scaffidi, Daniel E. Parker, Romain Vasseur Jan 2017

Gapless Symmetry-Protected Topological Order, Thomas Scaffidi, Daniel E. Parker, Romain Vasseur

Physics Department Faculty Publication Series

We introduce exactly solvable gapless quantum systems in d dimensions that support symmetry-protected topological (SPT) edge modes. Our construction leads to long-range entangled, critical points or phases that can be interpreted as critical condensates of domain walls “decorated” with dimension (d−1) SPT systems. Using a combination of field theory and exact lattice results, we argue that such gapless SPT systems have symmetry-protected topological edge modes that can be either gapless or symmetry broken, leading to unusual surface critical properties. Despite the absence of a bulk gap, these edge modes are robust against arbitrary symmetry-preserving local perturbations near the edges ...


Dynamical Mechanisms Leading To Equilibration In Two-Component Gases, Stephan De Bievre, Carlos Mejia-Monasterio, Paul Ernest Parris May 2016

Dynamical Mechanisms Leading To Equilibration In Two-Component Gases, Stephan De Bievre, Carlos Mejia-Monasterio, Paul Ernest Parris

Physics Faculty Research & Creative Works

Demonstrating how microscopic dynamics cause large systems to approach thermal equilibrium remains an elusive, longstanding, and actively pursued goal of statistical mechanics. We identify here a dynamical mechanism for thermalization in a general class of two-component dynamical Lorentz gases and prove that each component, even when maintained in a nonequilibrium state itself, can drive the other to a thermal state with a well-defined effective temperature.


Organic Solar Cells: Electrodes, Performance Enhancement And Degradation Mechanisms, Reginald J. Bauld Dec 2014

Organic Solar Cells: Electrodes, Performance Enhancement And Degradation Mechanisms, Reginald J. Bauld

Electronic Thesis and Dissertation Repository

In this thesis I focus on a number of aspects associated with the fabrication and characterization of organic photovoltaics. Specifically, my work focuses on evaluating solution processed graphene electrodes for use in organic photovoltaics, improving the performance of indium tin oxide transparent contacts by coating them with Au nanoparticles, and understanding the degradation pathways of Poly(3-hexylthiophene-2,5-diyl): Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) organic solar cells. In my work on graphene electrodes for organic solar cells I worked out a relationship between the sheet resistance and the film transmittance that is useful to optimize such electrodes. Investigation of organic ...


Nonlinear Magnetic Dynamics And The Switching Phase Diagrams In Spintronic Devices, Shu Anthoney Yan Jan 2014

Nonlinear Magnetic Dynamics And The Switching Phase Diagrams In Spintronic Devices, Shu Anthoney Yan

Theses and Dissertations

Spin-transfer torque induced magnetic switching, by which the spin-polarized current transfers its magnetic moment to the ferromagnetic layer and changes its magnetization, holds great promise towards faster and smaller magnetic bits in data-storage applications due to the lower power consumption and better scalability.

We propose an analytic approach which can be used to calculate the switching phase diagram of a nanomagnetic system in the presence of both magnetic field and spin-transfer torque in an exact fashion. This method is applied to the study of switching conditions for the uniaxial, single domain magnetic layers in different spin-transfer devices. In a spin ...


Haldane Pseudopotentials And Landau Level Mixing In The Quantum Hall Effect, Rachel Elizabeth Wooten May 2013

Haldane Pseudopotentials And Landau Level Mixing In The Quantum Hall Effect, Rachel Elizabeth Wooten

Doctoral Dissertations

The discovery of the quantum Hall effect in 1980 opened to physics one of the simplest systems for studying many-body correlations. Numerical techniques and trial wavefunctions have proven useful for describing the novel collective behavior of the electrons, but have not fully explained all features of the fractional quantum Hall effect. For example, it is predicted that Landau level mixing should have a moderate effect on the system for all but the very strongest magnetic fields, but this effect has not been extensively studied. Among the tools most useful to modeling and describing the quantum Hall system is the Haldane ...


Ab-Initio And Model Studies Of Spin Fluctuation Effects In Transport And Thermodynamics Of Magnetic Metals, James K. Glasbrenner Mar 2013

Ab-Initio And Model Studies Of Spin Fluctuation Effects In Transport And Thermodynamics Of Magnetic Metals, James K. Glasbrenner

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

Magnetic materials are vital to many devices and the manipulation of spins is central to the operation of novel devices such as spin transistors. It is important to understand the effect of spin fluctuations on such systems. In this dissertation, first-principles calculations and models further the understanding of spin fluctuation effects in the transport and thermodynamics of magnetic metals.

A simple classical spin-fluctuation Hamiltonian with a single itinerancy parameter is studied using the mean-field approximation, Monte Carlo simulations, and a generalized Onsager cavity field method. The results of these different methods are in agreement. It is found that the thermodynamics ...


Superconducting Nafe1-Xcoxas: Crystal Growth, Resistivity, And Susceptibility Measurements, Tucker Netherton May 2012

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

Chancellor’s Honors Program Projects

No abstract provided.


Approach To Accurately Measuring The Speed Of Optical Precursors, Chuan-Feng Li, Zong-Quan Zhou, Heejeong Jeong, Guang-Can Guo Oct 2011

Approach To Accurately Measuring The Speed Of Optical Precursors, Chuan-Feng Li, Zong-Quan Zhou, Heejeong Jeong, Guang-Can Guo

Open Dartmouth: Faculty Open Access Scholarship

Precursors can serve as a bound on the speed of information with dispersive medium. We propose a method to identify the speed of optical wavefronts using polarization-based interference in a solid-state device, which can bound the accuracy of the speed of wavefronts to less than 10−4 with conventional experimental conditions. Our proposal may have important implications for optical communications and fast information processing.


Combinatorial Fabrication & Studies Of Small Molecular Organic Light Emitting Devices (Oleds) And Structurally Integrated Oled-Based Chemical And Biological Sensors, Zhaoqun Zhou Jan 2007

Combinatorial Fabrication & Studies Of Small Molecular Organic Light Emitting Devices (Oleds) And Structurally Integrated Oled-Based Chemical And Biological Sensors, Zhaoqun Zhou

Retrospective Theses and Dissertations

No abstract provided.


Self Assembled Nano-Structures Of Pb On Si(111) Studied By Spa-Leed: Quantum Size Effect Driven Pb Islands And The "Devil's Staircase" , Michael Keith Yakes Jan 2006

Self Assembled Nano-Structures Of Pb On Si(111) Studied By Spa-Leed: Quantum Size Effect Driven Pb Islands And The "Devil's Staircase" , Michael Keith Yakes

Retrospective Theses and Dissertations

An important goal in present day surface science is to grow uniform sized self-assembled nanostructures. One system which has displayed a number of interesting surface structures is Pb grown on a Si(111) substrate. The first part of the thesis discusses the "Devil's Staircase" (DS) of linear phases studied with Scanning Tunneling Microscopy (STM) and Spot-Profile Analysis Low Energy Electron Diffraction (SPA-LEED). The DS is one of the outstanding predictions in theoretical physics and is expected to exist in systems with two competing interactions. It was found that at low temperatures (<120>K) over 15 different DS phases can be ...


Designing Of Metallic Photonic Structures And Applications , Yong-Sung Kim Jan 2006

Designing Of Metallic Photonic Structures And Applications , Yong-Sung Kim

Retrospective Theses and Dissertations

In this thesis our main interest has been to investigate metallic photonic crystal and its applications. We explained how to solve a periodic photonic structure with transfer matrix method and when and how to use modal expansion method. Two different coating methods were introduced, modifying a photonic structure's intrinsic optical properties and rigorous calculation results are presented;Two applications of metallic photonic structures are introduced. For thermal emitter, we showed how to design and find optimal structure. For conversion efficiency increasing filter, we calculated its efficiency and the way to design it.


Quantum Monte Carlo Calculations Applied To Magnetic Molecules , Larry Paul Engelhardt Jan 2006

Quantum Monte Carlo Calculations Applied To Magnetic Molecules , Larry Paul Engelhardt

Retrospective Theses and Dissertations

In this dissertation, we have implemented a quantum Monte Carlo (QMC) algorithm, and have used it to perform calculations for a variety of finite Heisenberg spin systems. A detailed description of the QMC method has been provided, which is followed by applications of the method to various systems. These applications begin with a detailed analysis of the (calculated) equilibrium magnetization and magnetic susceptibility for a number of Heisenberg Hamiltonians. In particular, we have studied the dependence of these quantities on intrinsic spin s, and have quantified the approach to the classical (s → infinity) limit. These results are not specific to ...


Soft-Lithographical Fabrication Of Three-Dimensional Photonic Crystals In The Optical Regime , Jae-Hwang Lee Jan 2006

Soft-Lithographical Fabrication Of Three-Dimensional Photonic Crystals In The Optical Regime , Jae-Hwang Lee

Retrospective Theses and Dissertations

This dissertation describes several projects to realize low-cost and high-quality three-dimensional (3D) microfabrication using non-photolithographic techniques for layer-by-layer photonic crystals. Low-cost, efficient 3D microfabrication is a demanding technique not only for 3D photonic crystals but also for all other scientific areas, since it may create new functionalities beyond the limit of planar structures. We have developed an advanced microtransfer molding technique, called two-polymer microtransfer molding (2P-[mu]TM) that shows an extremely high yield in layer-by-layer microfabrication sufficient to produce highly layered microstructures. The use of two different photo-curable prepolymers, a filler and an adhesive, allows for fabrication of layered ...


Investigations Of The Rni2ge2 Intermetallic Compounds By X-Ray Resonant Magnetic Scattering , Jong-Woo Kim Jan 2005

Investigations Of The Rni2ge2 Intermetallic Compounds By X-Ray Resonant Magnetic Scattering , Jong-Woo Kim

Retrospective Theses and Dissertations

The x-ray magnetic scattering (XRMS) intensities of the Gd, Tb, Dy, Ho, Er, and Tm L2,3 edges were investigated using two isostructural samples [Gd1/4Tb1/4Dy1/4Ho 1/4]Ni2Ge2 and [Gd1/3Er1/3Tm 1/3]Ni2Ge2 in order to elucidate systematics in the underlying resonance process. Taken together with theoretical linearized augmented planewave (LAPW) calculations employing LDA + U, we found that the XRMS intensity at the heavy rare-earth L edges is strongly related to the 4f-5d exchange interaction and that the branching ratio arises from the effects of spin orbit coupling in the 5d band. For Gd, the ...


Field-Induced Magnetic Phase Transitions And Correlated Electronic States In The Hexagonal Ragge And Rptin Series , Emilia Morosan Jan 2005

Field-Induced Magnetic Phase Transitions And Correlated Electronic States In The Hexagonal Ragge And Rptin Series , Emilia Morosan

Retrospective Theses and Dissertations

Rare earth intermetallic compounds provide rich grounds for investigating the properties of both local moment and strongly correlated, hybridized moment systems. These areas have been intensively explored mostly on cubic and tetragonal intermetallic compounds, and very little work existed on materials with lower symmetry. Moreover, a large number of Ce-based heavy fermion compounds have been studied, whereas the analogous Yb-based ones are much rarer. We thus wanted to study local moment metamagnetism and Yb-based heavy fermion physics in hexagonal systems.;The RAgGe and RPtIn series belonging to the Fe2P family of hexagonal compounds allowed us to perform such studies on ...


Spin Models For The Single Molecular Magnet Mn12-Ac , Mohamad A. Al-Saqer Jan 2005

Spin Models For The Single Molecular Magnet Mn12-Ac , Mohamad A. Al-Saqer

Retrospective Theses and Dissertations

The single molecular magnet (SMM) Mn12-AC attracted the attention of scientists since the discovery of its magnetic hystereses which are accompanied by sudden jumps in magnetic moments at low temperature. Unlike conventional bulk magnets, hysteresis in SMMs is of molecular origin. This qualifies them as candidates for next generation of high density storage media where a molecule which is at most few nanometers in size can be used to store a bit of information. However, the jumps in these hystereses, due to spin tunneling, can lead to undesired loss of information.;Mn12-AC molecule contains twelve magnetic ions antiferromagnetically coupled by ...


Tuning The Superconducting Properties Of Magnesium Diboride , Rudeger Heinrich Theoderich Wilke Jan 2005

Tuning The Superconducting Properties Of Magnesium Diboride , Rudeger Heinrich Theoderich Wilke

Retrospective Theses and Dissertations

The changes in normal state and superconducting properties of MgB 2 as a result of various perturbations have been investigated. Carbon doping was achieved using a two step reaction process wherein boron filaments were doped with carbon via a chemical vapor deposition technique. The subsequent filaments were then exposed to magnesium vapor to form the superconducting phase. Studies on the effects of defects introduced by neutron irradiation were performed on both pure and carbon doped MgB2 wires that were exposed to thermal neutron fluences in the range 1018-10 19 n/cm2;Different techniques for synthesizing carbon doped MgB2 powders were ...


Modeling Of Deposition And Reaction Processes On Si(100) , Marvin Argulla Albao Jan 2005

Modeling Of Deposition And Reaction Processes On Si(100) , Marvin Argulla Albao

Retrospective Theses and Dissertations

In this dissertation, we analyzed selected deposition and reaction processes on Si(100) using Kinetic Monte Carlo (KMC) simulation of suitable atomistic lattice-gas models. For the first project on the room-temperature deposition of Ga on Si(100), analysis of the island size distribution reveals that it is monotonically decreasing rather than monomodal, a clear departure from classical nucleation theory. KMC simulations of a realistic model recover this behavior, and simulations of refined models show that aggregation is responsible for the unexpected shape of the island size distribution. From these simulations, we were also able to extract reasonable values for the ...


Theoretical Studies Of Pb On Si(111) And Si(100), Global Search For H-Passivated Si Nanowires, And Construction Of Highly Localized Quasiatomic Minimal Basis Orbitals For Mo , Tzu-Liang Chan Jan 2005

Theoretical Studies Of Pb On Si(111) And Si(100), Global Search For H-Passivated Si Nanowires, And Construction Of Highly Localized Quasiatomic Minimal Basis Orbitals For Mo , Tzu-Liang Chan

Retrospective Theses and Dissertations

By first-principles calculations, we have performed extensive studies for the structures of Pb on Si(111) at low coverage. Relative stabilities between these low coverage phases were compared and comparison with scanning tunneling microscopy (STM) experiments were made. By tight-binding molecular dynamics simulations, we discovered that there are significant atomic rearrangements at the Pb/Si interface of the Pb islands on Si(111), which can lead to a change in the electronic structures of ultra-thin Pb films predicted by quantum size effect. In particular, the electronic behavior of nano-scale Moire pattern observed in STM for ultra-thin Pb films on Si ...


Optically Detected Magnetic Resonance (Odmr) Measurements On Conjugated Polymers And Studies Of Poly-(N-Vinyl Carbazole) (Pvk) Based Leds, Moon-Ky Lee Jan 2005

Optically Detected Magnetic Resonance (Odmr) Measurements On Conjugated Polymers And Studies Of Poly-(N-Vinyl Carbazole) (Pvk) Based Leds, Moon-Ky Lee

Retrospective Theses and Dissertations

The Origin of the PLDMR enhancing signal and various aspects of the device physics of small molecular doped PLEDs were described and discussed. The difference between the delay model and the quenching model was explained. The microwave- and laser-modulation-frequency dependence of the PLDMR and DM-PLDMR, respectively, in MEH-PPV, invalidated the delay models, questioning reports of SE yields exceeding 25% in fluorescent OLEDs. Rather, the results were consistent with the quenching model where SEs are annihilated by TEs and polarons. For the device, the proper procedure for the treatment of the PEDOT/PSS layer with EG was suggested and a 10 ...


Theoretical Investigation Of Dynamic Properties Of Magnetic Molecule Systems As Probed By Nmr And Pulsed Fields Experiments , Ioannis Rousochatzakis Jan 2005

Theoretical Investigation Of Dynamic Properties Of Magnetic Molecule Systems As Probed By Nmr And Pulsed Fields Experiments , Ioannis Rousochatzakis

Retrospective Theses and Dissertations

In this dissertation we theoretically investigate static and especially dynamic properties of magnetic molecules (MM's), as probed by the nuclear spin lattice relaxation rate 1/T1 (first part) and pulsed fields measurements of the magnetization M( t) (second part). In the first part, we provide a general first-principles account for 1/T1, which incorporates the decay of spin fluctuations and the corresponding "broadening" of the discrete magnetic energy levels of MM's. This is achieved by including the interaction of the electronic moments with the local deformation of the host lattice (phonons), in the Markovian regime and employing the ...


Theory For Dynamical Self Arrest And Gelation In Microemulsions And The Block Copolymer Systems , Sangwook Wu Jan 2005

Theory For Dynamical Self Arrest And Gelation In Microemulsions And The Block Copolymer Systems , Sangwook Wu

Retrospective Theses and Dissertations

Complex materials like microemulsions and block copolymers exhibit ordinary phase transitions but also various crossover and slow dynamics, reminescent of gels and glasses. Using a replica approach, we present a theory for self generated randomness in such systems. This yields a dynamical arrest similar to what occurs in a structural glasses with Kauzmann temperature, TK, and dynamical crossover temperature, TA, at which the viscosity diverges within mode coupling theory. In the region TK < T < TA, the numerous metastable states becomes exponentially large and the system's dynamics becomes very slow, eventually leading to glassy behavior. We use analytical and numerical methods combined with the replica approach to study uniformly frustrated system such as microemulsions and block copolymers.;A dynamical self arrest in microemulsions and in block copolymers for different volume fraction, f(f = SA/S) and a physical gelation of a triblock copolymer with a hydrophobic end groups will be discussed.


Photoemission Study Of The Rare Earth Intermetallic Compounds: Rni2ge2(R=Eu, Gd) , Jongik Park Jan 2004

Photoemission Study Of The Rare Earth Intermetallic Compounds: Rni2ge2(R=Eu, Gd) , Jongik Park

Retrospective Theses and Dissertations

The electronic structures of EuNi2Ge2 and GdNi 2Ge2 have been investigated using photoemission spectroscopy. The majority of the photoemission intensity near EF was due to the mostly Ni 3d states in both materials. CIS spectra were recorded at selected initial-state binding energies (BEs) across the excitation energy range of the Ni 3p threshold in EuNi 2Ge2. It is apparent that there is strong Ni d character throughout the valence band from CIS spectra. Resonance measurements of the Eu 4d→4f excitations in EuNi 2Ge2 reveal that Eu 4f states are localized around 2 eV below EF. It is observed that ...


A Threading Approach To Protein Structure Prediction: Studies On Tnf-Like Molecules, Rev Proteins, And Protein Kinases , Yungok Ihm Jan 2004

A Threading Approach To Protein Structure Prediction: Studies On Tnf-Like Molecules, Rev Proteins, And Protein Kinases , Yungok Ihm

Retrospective Theses and Dissertations

The main focus of this dissertation is the application of the threading approach to specific biological problems. The threading scheme developed in our group targets incorporating important structural features necessary for detecting structural similarity between the target sequence and the template structure. This enables us to use our threading method to solve problems for which sequence-based methods are not very much useful. We applied our threading method to predict the three-dimensional structures of lentivirus (EIAV, HIV-1, FIV, SIV) Rev proteins. Predicted structures of Rev proteins suggest that they share a structural similarity among themselves (four-helix bundle). Also, the threading approach ...


Optical And Magneto-Optic Kerr Effects Of Mnbi, Ni2mnga, And Gd5si2ge2 , Joong-Mok Park Jan 2004

Optical And Magneto-Optic Kerr Effects Of Mnbi, Ni2mnga, And Gd5si2ge2 , Joong-Mok Park

Retrospective Theses and Dissertations

The magneto-optic Kerr angle spectrum of a single crystal of MnBi was measured at room temperature and also calculated with the TB-LMTO methods including the spin-orbit interaction. Previously measured Kerr spectra with thin films had two negative peaks, except for one film grown in ultra high vacuum. The later had a first peak and a shoulder at the second peak position, indicating the second originated from oxygen in the other films. Comparing first-principles calculations and previous thin-film results with our single crystal data indicated that the second peak originated from the combination of a weak intrinsic MnBi peak and oxygen ...


Spin Dynamics And Quantum Tunneling In Fe8 Nanomagnet And In Afm Rings By Nmr , Seung-Ho Baek Jan 2004

Spin Dynamics And Quantum Tunneling In Fe8 Nanomagnet And In Afm Rings By Nmr , Seung-Ho Baek

Retrospective Theses and Dissertations

In this thesis, our main interest has been to investigate the spin dynamics and quantum tunneling in single molecule magnets (SMMs). For this we have selected two different classes of SMMs: a ferromagnetic total high spin S = 10 cluster Fe8 and antiferromagnetic (AFM) ring-type clusters. For Fe8, our efforts have been devoted to the investigation of the quantum tunneling of magnetization in the very low temperature region. The most remarkable experimental finding in Fe8 is that the nuclear spin-lattice relaxation rate (1/T1) at low temperatures takes place via strong collision mechanism, and thus it allows to measure directly the ...


First Principles Calculations For X-Ray Resonant Spectra And Elastic Properties , Yongbin Lee Jan 2004

First Principles Calculations For X-Ray Resonant Spectra And Elastic Properties , Yongbin Lee

Retrospective Theses and Dissertations

In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching ratio problem in the heavy rare earths L3, L2-edges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB 14.


Protein Structure Recognition: From Eigenvector Analysis To Structural Threading Method , Haibo Cao Jan 2003

Protein Structure Recognition: From Eigenvector Analysis To Structural Threading Method , Haibo Cao

Retrospective Theses and Dissertations

In this work, we try to understand the protein folding problem using pair-wise hydrophobic interaction as the dominant interaction for the protein folding process. We found a strong correlation between amino acid sequence and the corresponding native structure of the protein. Some applications of this correlation were discussed in this dissertation include the domain partition and a new structural threading method as well as the performance of this method in the CASP5 competition.;In the first part, we give a brief introduction to the protein folding problem. Some essential knowledge and progress from other research groups was discussed. This part ...


Electromagnetic Wave Propagation In Two-Dimensional Photonic Crystals , Stavroula Foteinopoulou Jan 2003

Electromagnetic Wave Propagation In Two-Dimensional Photonic Crystals , Stavroula Foteinopoulou

Retrospective Theses and Dissertations

In this dissertation, we have undertaken the challenge to understand the unusual propagation properties of the photonic crystal (PC)---a medium with periodically modulated dielectric function. PCs have frequency regions were propagation is prohibited (gaps) and regions where propagation is allowed (bands). We first study a two-dimensional (2D) photonic crystal system in the gap region. A line defect introduces allowed states in an otherwise prohibited frequency spectrum. The dependence of the defect resonance state on the system's parameters, such as the lateral width of the structure and the profile of the source, is investigated in detail. Subsequently, we examine ...


Spin Dynamics In Molecular Nanomagnets At Intermediate Temperatures: An Nmr And [Mu]Sr Investigation , Daniele Procissi Jan 2003

Spin Dynamics In Molecular Nanomagnets At Intermediate Temperatures: An Nmr And [Mu]Sr Investigation , Daniele Procissi

Retrospective Theses and Dissertations

Solid lattices of weakly coupled magnetic molecules provide an unique opportunity to study magnetism at a nanoscale level. Each non interacting molecule in the lattice represents a single nanomagnet composed of only a few magnetic moments. These magnetic moments are coupled to each other via exchange interaction. The overall magnetic properties of molecules are entirely ascribed to these few magnetic moments. In order to investigate the spin dynamics of these systems as a function of temperature and external magnetic field we performed an extensive experimental investigation using nuclear magnetic resonance (NMR) and muon rotation spectroscopy (muSR) techniques. The aim of ...