Kinetics Of The Crystal-Melt Phase Transformation In Semicrystalline Polymers, 2020 University of Massachusetts Amherst

#### Kinetics Of The Crystal-Melt Phase Transformation In Semicrystalline Polymers, Kiran Subramaniam Iyer

*Doctoral Dissertations*

The assembly of long-chain polymers into an ordered state is a process that has puzzled polymer scientists for several decades. A process that is largely controlled by the strength of intermolecular attractions in small molecular systems, this crystallization in the case of polymers is controlled by a competition between the aforementioned force of attraction between monomers and the formidable conformational entropy of polymer chains. Any factor that affects this conformational entropy, whether that is an equilibrium thermodynamic factor or a kinetic factor, has the ability to control polymer crystallization. In this thesis, we focus on understanding the underlying kinetic processes ...

Intrinsic Axion Insulating Behavior In Antiferromagnetic Mnbi6te10, 2020 Iowa State University and Ames Laboratory

#### Intrinsic Axion Insulating Behavior In Antiferromagnetic Mnbi6te10, Na Hyun Jo, Lin-Lin Wang, Robert-Jan Slager, Jiaqiang Yan, Yun Wu, Kyungchan Lee, Benjamin Schrunk, Ashvin Vishwanath, Adam Kaminski

*Ames Laboratory Accepted Manuscripts*

A striking feature of time-reversal symmetry (TRS) protected topological insulators (TIs) is that they are characterized by a half integer quantum Hall effect on the boundary when the surface states are gapped by time-reversal breaking perturbations. While TRS-protected TIs have become increasingly under control, magnetic analogs are still a largely unexplored territory with novel rich structures. In particular, magnetic topological insulators can also host a quantized axion term in the presence of lattice symmetries. Since these symmetries are naturally broken on the boundary, the surface states can develop a gap without external manipulation. In this paper, we combine theoretical analysis ...

Ferromagnetic Cluster-Glass Phase In Ca(Co1-Xirx)(2-Y)As-2 Crystals, 2020 Ames Laboratory

#### Ferromagnetic Cluster-Glass Phase In Ca(Co1-Xirx)(2-Y)As-2 Crystals, Santanu Pakhira, N. S. Sangeetha, Volodymyr Smetana, Anja-Verena Mudring, David C. Johnston

*Ames Laboratory Accepted Manuscripts*

Single crystals of Ca(Co1−xIrx)2−yAs2 with 0≤x≤0.35 and 0.10≤y≤0.14 have been grown using the self-flux technique and characterized by single-crystal x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy, magnetization M, and magnetic susceptibility χ measurements versus temperature T, magnetic field H, and time t, and heat-capacity Cp(H,T) measurements. The XRD refinements reveal that all the Ir-substituted crystals crystallize in a collapsed-tetragonal structure as does the parent CaCo2−yAs2 compound. A small 3.3% Ir substitution for Co in CaCo1.86As2 drastically lowers the A-type antiferromagnetic (AFM) transition temperature TN from ...

Quantum Criticality In Strongly Correlated Electron Systems, 2020 Louisiana State University and Agricultural and Mechanical College

#### Quantum Criticality In Strongly Correlated Electron Systems, Samuel Obadiah Kellar

*LSU Doctoral Dissertations*

The study of the Hubbard model in three dimensions contains a variety of phases dependent upon the chosen parameters. This thesis shows that there is the indication of a zero temperature phase transition at a finite doping. The Hubbard model has been used to identify a similar quantum critical point in two dimensions. The presented results continue these investigations. The system demonstrates a strange metal phase at finite temperature which cannot be described in term of the conventional Fermi liquid. While there have been extensive studies over the past three decades for such materials in two dimensions, there are few ...

Interaction Between Moving Abrikosov Vortices In Type-Ii Superconductors, 2020 Ames Laboratory

#### Interaction Between Moving Abrikosov Vortices In Type-Ii Superconductors, Vladimir G. Kogan, Ruslan Prozorov

*Ames Laboratory Accepted Manuscripts*

The self-energy of a moving vortex is shown to decrease with increasing velocity. The interaction energy of two parallel slowly moving vortices differs from the static case by a small term ∝v2; the “slow” motion is defined as having the velocity vvc(T), the interaction energy of two vortices situated along the velocity direction is enhanced and in the perpendicular direction is suppressed compared to the static case.

Identifying Structure Transitions Using Machine Learning Methods, 2020 Louisiana State University

#### Identifying Structure Transitions Using Machine Learning Methods, Nicholas Walker

*LSU Doctoral Dissertations*

Methodologies from data science and machine learning, both new and old, provide an exciting opportunity to investigate physical systems using extremely expressive statistical modeling techniques. Physical transitions are of particular interest, as they are accompanied by pattern changes in the configurations of the systems. Detecting and characterizing pattern changes in data happens to be a particular strength of statistical modeling in data science, especially with the highly expressive and flexible neural network models that have become increasingly computationally accessible in recent years through performance improvements in both hardware and algorithmic implementations. Conceptually, the machine learning approach can be regarded as ...

Search For Encapsulation Of Platinum, Silver, And Gold At The Surface Of Graphite, 2020 Iowa State University and Ames Laboratory

#### Search For Encapsulation Of Platinum, Silver, And Gold At The Surface Of Graphite, Ann Lii-Rosales, Yong Han, Dapeng Jing, Michael C. Tringides, Patricia A. Thiel

*Chemistry Publications*

Using scanning tunneling microscopy, we show that Pt clusters can be encapsulated beneath the surface of graphite, whereas Ag and Au cannot. This is in complete agreement with independent predictions from density functional theory, which show that surface intercalation of single metal atoms is favorable for Pt, but unfavorable for Ag and Au. This supports the validity of using single-metal-atom energetics for predicting encapsulation of metal nanoparticles at the graphite surface. We also demonstrate that the optimal temperature for encapsulation scales with the cohesive energy of the metal.

Multi-Metallic Conduction Cooled Superconducting Radio-Frequency Cavity With High Thermal Stability, 2020 Old Dominion University

#### Multi-Metallic Conduction Cooled Superconducting Radio-Frequency Cavity With High Thermal Stability, Gianluigi Ciovati, Gary Cheng, Uttar Pudasaini, Robert A. Rimmer

*Physics Faculty Publications*

Superconducting radio-frequency cavities are commonly used in modern particle accelerators for applied and fundamental research. Such cavities are typically made of high-purity, bulk Nb and with cooling by a liquid helium bath at a temperature of ∼2 K. The size, cost and complexity of operating a particle accelerator with a liquid helium refrigerator make the current cavity technology not favorable for use in industrial-type accelerators. We have developed a multi-metallic 1.495 GHz elliptical cavity conductively cooled by a cryocooler. The cavity has a ∼2* μm* thick layer of Nb_{3}Sn on the inner surface, exposed to the rf ...

Tuning The Intrinsic Anisotropy With Disorder In The Cakfe4as4 Superconductor, 2020 Politecnico di Torino and Istituto Nazionale di Fisica Nucleare

#### Tuning The Intrinsic Anisotropy With Disorder In The Cakfe4as4 Superconductor, D. Torsello, G. A. Ummarino, J. Bekaert, L. Gozzelino, R. Gerbaldo, Makariy A. Tanatar, Paul C. Canfield, Ruslan Prozorov, G. Ghigo

*Ames Laboratory Accepted Manuscripts*

We report on the anisotropy of the London penetration depth of CaKFe4As4, discussing how it relates to its electronic structure and how it modifies under introduction of disorder, both chemically induced (by Ni substitution) and irradiation induced (by 3.5-MeV protons). Indeed, CaKFe4As4 is particularly suitable for the study of fundamental superconducting properties due to its stoichiometric composition, exhibiting clean-limit behavior in the pristine samples and having a fairly high critical temperature, Tc≈35 K. The London penetration depth λL is measured with a microwave-coplanar-resonator technique that allows us to deconvolve the anisotropic contributions λL,ab and λL,c and ...

Local Density Of Optical States In The Three-Dimensional Band Gap Of A Finite Photonic Crystal, 2020 University of Crete and Foundation for Research and Technology Hellas

#### Local Density Of Optical States In The Three-Dimensional Band Gap Of A Finite Photonic Crystal, Charalampos P. Mavidis, Anna C. Tasolamprou, Shakeeb B. Hasan, Thomas Koschny, Eleftherios N. Economou, Maria Kafesaki, Costas M. Soukoulis, Willem L. Vos

*Ames Laboratory Accepted Manuscripts*

A three-dimensional (3D) photonic band gap crystal is an ideal tool to completely inhibit the local density of optical states (LDOS) at every position in the crystal throughout the band gap. This notion, however, pertains to ideal infinite crystals, whereas any real crystal device is necessarily finite. This raises the question as to how the LDOS in the gap depends on the position and orientation inside a finite-size crystal. Therefore, we employ rigorous numerical calculations using finite-difference time domain simulations of 3D silicon inverse woodpile crystals filled with air or with toluene, as previously studied in experiments. We find that ...

Role Of Nonlocality In Exchange Correlation For Magnetic Two-Dimensional Van Der Waals Materials, 2020 Ames Laboratory

#### Role Of Nonlocality In Exchange Correlation For Magnetic Two-Dimensional Van Der Waals Materials, Yongbin Lee, Takao Kotani, Liqin Ke

*Ames Laboratory Accepted Manuscripts*

To obtain accurate independent-particle descriptions for ferromagnetic two-dimensional van der Waals materials, we apply the quasiparticle self-consistent GW (QSGW) method to VI3, CrI3, CrGeTe3, and Fe3GeTe2. QSGW provides a description of the nonlocal exchange-correlation term in the one-particle Hamiltonian. The nonlocal term is important not only as the U of density functional theory (DFT) + U but also for differentiating occupied and unoccupied states in semiconductors. We show the limitations of DFT + U in mimicking QSGW.

Quantum Interference In Monocyclic Molecules: A Novel And Straightforward Phase Wave Model, 2020 Al-Qasim Green University

#### Quantum Interference In Monocyclic Molecules: A Novel And Straightforward Phase Wave Model, Zainelabideen Yousif Mijbil

*Karbala International Journal of Modern Science*

We have proposed by far the simplest model, so-called phase wave model (PWM), to predict quantum interference states in monocyclic molecules. Meanwhile, transmission coefficient calculations were also performed using Green’s function method incorporated with Hückel (Tight Binding) approximation. An impressive agreement has been obtained between the results of the phase wave model and the ones from transmission coefficient calculations for the chosen model systems, namely benzene, cycloheptatriene, cyclooctatetraene, and [10]annulene. PWM represents the phase of wave functions of the incoming electrons by a wave and associates a single wavelength of the phase with five atoms/sites. Hence, the ...

Universal Temperature Dependence Of The London Penetration Depth In Κ−(Et)2x Superconductors, 2020 University of Illinois at Urbana-Champaign

#### Universal Temperature Dependence Of The London Penetration Depth In Κ−(Et)2x Superconductors, R. W. Giannetta, T. A. Olheiser, J. A. Schlueter, Makariy A. Tanatar, Ruslan Prozorov

*Ames Laboratory Accepted Manuscripts*

High-precision radio-frequency magnetic susceptibility measurements were performed on single crystals of fully deuterated kappa-(ET)(2)Cu[N(CN)(2)]Br, hereafter designated as kappa-(D8 ET)(2)Cu[N(CN)(2)]Br. This material phase separates into superconducting and antiferromagnetic regions, the degree of which depends strongly upon the cooling rate. We show that the screening fraction rise varies logarithmically with the cooling rate over nearly five decades. The average size of superconducting regions is estimated to vary from 5 to 40 mu m, depending upon cooling rate, consistent with previous infrared microscopy measurements. In the region T less ...

Unveiling The Medium-Range Order In Glass Models And Its Role In Glass Formation, 2020 Southern University of Science and Technology

#### Unveiling The Medium-Range Order In Glass Models And Its Role In Glass Formation, Xinyu Fan, Yang Sun, Cai-Zhuang Wang, Kai-Ming Ho, M. S. Altman, Li Huang

*Ames Laboratory Accepted Manuscripts*

The correlation between structure and glass formability in glassy systems is a long-standing puzzle. To solve this puzzle, many descriptors based on the short-range order (SRO) have been proposed. Here we show that the SRO, however, offers little help in explaining the glass formability and stability; instead it is the formation of medium-range order that stabilizes the glass against crystallization by suppressing the atomic rearrangement and compositional change. Our results provide a perspective for understanding the correlation between structure and stability in glasses

Generalized Magnetoelectronic Circuit Theory And Spin Relaxation At Interfaces In Magnetic Multilayers, 2020 University of Nebraska - Lincoln

#### Generalized Magnetoelectronic Circuit Theory And Spin Relaxation At Interfaces In Magnetic Multilayers, G. G. Baez Flores, Alexey Kovalev, Mark Van Schilfgaarde, K. D. Belashchenko

*Faculty Publications, Department of Physics and Astronomy*

Spin transport at metallic interfaces is an essential ingredient of various spintronic device concepts, such as giant magnetoresistance, spin-transfer torque, and spin pumping. Spin-orbit coupling plays an important role in many such devices. In particular, spin current is partially absorbed at the interface due to spin-orbit coupling. We develop a general magnetoelectronic circuit theory and generalize the concept of spin-mixing conductance, accounting for various mechanisms responsible for spin-flip scattering. For the special case when exchange interactions dominate, we give a simple expression for the spin-mixing conductance in terms of the contributions responsible for spin relaxation (i.e., spin memory loss ...

Fabrication Of Magnetocaloric La(Fe,Si)13 Thick Films, 2020 Université Grenoble Alpes

#### Fabrication Of Magnetocaloric La(Fe,Si)13 Thick Films, N H. Dung, N B. Doan, P De Rango, L Ranno, Karl G. Sandeman, N M. Dempsey

*Publications and Research*

La(Fe,Si)_{13}–based compounds are considered to be very promising magnetocaloric materials for magnetic refrigeration applications. Many studies have focused on this material family but only in bulk form. In this paper we report on the fabrication of thick films of La(Fe,Si)_{13}, both with and without post-hydriding. These films exhibit magnetic and structural properties comparable to bulk materials. We also observe that the ferromagnetic phase transition has a negative thermal hysteresis, a phenomenon not previously found in this material but which may have its origins in the availability of a strain energy reservoir, as in ...

Exceedingly Small Moment Itinerant Ferromagnetism Of Single Crystalline La5co2ge3, 2020 Iowa State University and Ames Laboratory

#### Exceedingly Small Moment Itinerant Ferromagnetism Of Single Crystalline La5co2ge3, Scott M. Saunders, Li Xiang, Rustem Khasanov, Tai Kong, Qisheng Lin, Sergey L. Bud’Ko, Paul C. Canfield

*Physics and Astronomy Publications*

Single crystals of monoclinic La5Co2Ge3 were grown using a self-flux method and were characterized by room-temperature powder x-ray diffraction, anisotropic temperature- and field-dependent magnetization, temperature-dependent resistivity, specific heat, and muon spin rotation. La5Co2Ge3 has a Curie temperature (T-C) of 3.8 K and clear signatures of ferromagnetism in magnetization and mu SR data, as well as a clear loss of spin disorder scattering in resistivity data and a sharp specific heat anomaly. The magnetism associated with La5Co2Ge3 is itinerant has a change in the entropy at T-C of similar or equal to 0.05R ln 2 per mol Co and ...

First-Order Magnetic Phase Transition In Pr2in With Negligible Thermomagnetic Hysteresis, 2020 Ames Laboratory

#### First-Order Magnetic Phase Transition In Pr2in With Negligible Thermomagnetic Hysteresis, Anis Biswas, N. A. Zarkevich, Arjun Pathak, Oleksandr Dolotko, Ihor Z. Hlova, A. V. Smirnov, Yaroslav Mudryk, Duane D. Johnson, Vitalij K. Pecharsky

*Materials Science and Engineering Publications*

Magnetic first-order phase transitions are key for the emergence of functionalities of fundamental and applied significance, including magnetic shape memory as well as magnetostrictive and magnetocaloric effects. Such transitions are usually associated with thermomagnetic hysteresis. We report the observation of a first-order transition in Pr2In from a paramagnetic to a ferromagnetic state at TC=57K without a detectable thermomagnetic hysteresis, which is also accompanied by a large magnetocaloric effect. The peculiar electronic structure of Pr2In exhibiting a large density of states near the Fermi energy explains the highly responsive magnetic behavior of the material. The magnetic properties of Pr2In are ...

Magnetic, Thermal, And Electronic-Transport Properties Of Eumg2bi2 Single Crystals, 2020 Ames Laboratory

#### Magnetic, Thermal, And Electronic-Transport Properties Of Eumg2bi2 Single Crystals, Santanu Pakhira, Makariy A. Tanatar, David C. Johnston

*Ames Laboratory Accepted Manuscripts*

The trigonal compound EuMg2Bi2 has recently been discussed in terms of its topological band properties. These are intertwined with its magnetic properties. Here detailed studies of the magnetic, thermal, and electronic-transport properties of EuMg2Bi2 single crystals are presented. The Eu+2 spins 7/2 in EuMg2Bi2 exhibit an antiferromagnetic (AFM) transition at a temperature T-N = 6.7 K, as previously reported. By analyzing the anisotropic magnetic susceptibility chi data below T-N in terms of molecular-field theory (MFT), the AFM structure is inferred to be a c-axis helix, where the ordered moments in the hexagonal ab-plane layers are aligned ferromagnetically in ...

Modeling Single Microtubules As A Colloidal System To Measure The Harmonic Interactions Between Tubulin Dimers In Bovine Brain Derived Versus Cancer Cell Derived Microtubules, 2020 New Jersey Institute of Technology

#### Modeling Single Microtubules As A Colloidal System To Measure The Harmonic Interactions Between Tubulin Dimers In Bovine Brain Derived Versus Cancer Cell Derived Microtubules, Arooj Aslam

*Dissertations*

The local properties of tubulin dimers dictate the properties of the larger microtubule assembly. In order to elucidate this connection, tubulin-tubulin interactions are be modeled as harmonic interactions to map the stiffness matrix along the length of the microtubule. The strength of the interactions are measured by imaging and tracking the movement of segments along the microtubule over time, and then performing a fourier transform to extract the natural vibrational frequencies. Using this method the first ever reported experimental phonon spectrum of the microtubule is reported. This method can also be applied to other biological materials, and opens new doors ...