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Condensed Matter Physics

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Full-Text Articles in Physics

Wave Propagation In Random And Topological Media, Yuhao Kang Sep 2020

Wave Propagation In Random And Topological Media, Yuhao Kang

Dissertations, Theses, and Capstone Projects

This thesis discusses wave propagation in two kinds of systems, random media and topological insulators. In a disordered system, the wave is randomized by multiple scattering. The scattering matrix and associated delay times are powerful tools with which to describe wave transport. We discuss the relation among the Wigner time, the transmission time, and energy density in a lossless or lossy system. We propose the zeros of the transmission matrix and show how to manipulate the zero-transmission mode in a nonunitary system. In a photonic topological insulator, we realize an edge mode and discuss its robustness in the face of ...


Emulating Condensed Matter Systems In Classical Wave Metamaterials, Matthew Weiner Sep 2020

Emulating Condensed Matter Systems In Classical Wave Metamaterials, Matthew Weiner

Dissertations, Theses, and Capstone Projects

One of the best tools we have for the edification of physics is the analogy. When we take our classical set of states and dynamical variables in phase space and treat them as vectors and Hermitian operators respectively in Hilbert space through the canonical quantization, we lose out on a lot of the intuition developed with the previous classical physics. With classical physics, through our own experiences and understanding of how systems should behave, we create easy-to-understand analogies: we compare the Bohr model of the atom to the motion of the planets, we compare electrical circuits to the flow of ...


Control Of Molecular Energetics And Transport Via Strong Light-Matter Interaction, Rong Wu Sep 2020

Control Of Molecular Energetics And Transport Via Strong Light-Matter Interaction, Rong Wu

Dissertations, Theses, and Capstone Projects

Strong light-matter coupling in excitonic systems results in the formation of half-light half-matter quasiparticles called exciton polaritons. These hybrid quasiparticles take on the best of both systems, namely, the long-range propagation and coherence arising from the photonic component and the nonlinear interaction from the excitonic component. We develop methods for making high quality factor cavities and investigate the potential applications of these strongly coupled states arising specifically in organic molecular systems.

In the first project we investigate the potential of organic dye molecules to undergo condensation in an optical cavity at room temperature. The second study involves the use of ...


Linear And Non-Linear Elastic Constants Of Crystalline Materials From First-Principles Calculations, David Cuffari Sep 2020

Linear And Non-Linear Elastic Constants Of Crystalline Materials From First-Principles Calculations, David Cuffari

Dissertations, Theses, and Capstone Projects

Novel methods based on the use of density functional theory (DFT) calculations are developed and applied to calculate linear and non-linear elastic constants of materials at zero and finite temperature. These methods rely on finite difference techniques and are designed to be general, numerically accurate, and suitable to investigate the thermoelastic properties of anharmonic materials. A first method was developed to compute the third-order elastic constants of crystalline materials at zero temperature, a task that is numerically challenging and is currently undertaken by using approaches typically applicable to cubic and hexagonal crystalline systems. This method relies on numerical differentiation of ...


Yield-Stress Fluids In Confined Geometries, Thalia Magyar Aug 2020

Yield-Stress Fluids In Confined Geometries, Thalia Magyar

Electronic Thesis and Dissertation Repository

A yield-stress fluid is a material that has properties of both solids and conventional liquids that only begins to flow when subject to a finite stress. The behaviour of yield-stress fluids is interesting and important in many applications. It is expected that the rheological properties of a yield-stress fluid will change when confined to a region with a length scale comparable to the characteristic scale of its microstructure. The particle size and polydispersity of two yield-stress fluids, Carbopol and poly(N-isopropylacrylamide), were determined using dynamic light scattering. A rheological characterization was performed on these two yield-stress fluids. Flow of ...


Understanding The Magnetic Properties Of Ii-Vi Semiconductor Nanocrystals, Alex Khammang Aug 2020

Understanding The Magnetic Properties Of Ii-Vi Semiconductor Nanocrystals, Alex Khammang

Electronic Theses and Dissertations

Semiconductor nanocrystals (NC) are well known for their unique size tunable optical properties making them suitable candidates for devices such as light emitting diodes (LEDs), solar cells, and cellular labels. II-VI semiconductors in the bulk form behave diamagnetically, but can inherit paramagnetic (PM) or ferromagnetic (FM) properties at the nanoscale. Reports suggest that the emergence of weak PM or FM behavior in undoped NCs are attributed to the increased surface to volume ratio compared for NCs. Traditionally, these NCs only obtain magnetic properties after doping with certain transition metals, such as Co, Mn, or Fe. Many mechanisms have been proposed ...


Fifth-Degree Elastic Energy For Predictive Continuum Stress–Strain Relations And Elastic Instabilities Under Large Strain And Complex Loading In Silicon, Hao Chen, Nikolai A. Zarkevich, Valery I. Levitas, Duane D. Johnson, Xiancheng Zhang Aug 2020

Fifth-Degree Elastic Energy For Predictive Continuum Stress–Strain Relations And Elastic Instabilities Under Large Strain And Complex Loading In Silicon, Hao Chen, Nikolai A. Zarkevich, Valery I. Levitas, Duane D. Johnson, Xiancheng Zhang

Aerospace Engineering Publications

Materials under complex loading develop large strains and often phase transformation via an elastic instability, as observed in both simple and complex systems. Here, we represent a material (exemplified for Si I) under large Lagrangian strains within a continuum description by a 5th-order elastic energy found by minimizing error relative to density functional theory (DFT) results. The Cauchy stress—Lagrangian strain curves for arbitrary complex loadings are in excellent correspondence with DFT results, including the elastic instability driving the Si I → II phase transformation (PT) and the shear instabilities. PT conditions for Si I → II under action of cubic axial ...


Free Charge Carrier Properties In Two-Dimensional Materials And Monoclinic Oxides Studied By Optical Hall Effect, Sean Knight Aug 2020

Free Charge Carrier Properties In Two-Dimensional Materials And Monoclinic Oxides Studied By Optical Hall Effect, Sean Knight

Theses, Dissertations, and Student Research from Electrical & Computer Engineering

In this dissertation, optical Hall effect (OHE) measurements are used to determine the free charge carrier properties of important two-dimensional materials and monoclinic oxides. Two-dimensional material systems have proven useful in high-frequency electronic devices due to their unique properties, such as high mobility, which arise from their two-dimensional nature. Monoclinic oxides exhibit many desirable characteristics, for example low-crystal symmetry which could lead to anisotropic carrier properties. Here, single-crystal monoclinic gallium oxide, an AlInN/GaN-based high-electron-mobility transistor (HEMT) structure, and epitaxial graphene are studied as examples. To characterize these material systems, the OHE measurement technique is employed. The OHE is a ...


Quantum Criticality In Strongly Correlated Electron Systems, Samuel Obadiah Kellar Jul 2020

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 ...


Identifying Structure Transitions Using Machine Learning Methods, Nicholas Walker Jul 2020

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, Ann Lii-Rosales, Yong Han, Dapeng Jing, Michael C. Tringides, Patricia A. Thiel Jul 2020

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, Gianluigi Ciovati, Gary Cheng, Uttar Pudasaini, Robert A. Rimmer Jul 2020

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 Nb3Sn on the inner surface, exposed to the rf ...


Quantum Interference In Monocyclic Molecules: A Novel And Straightforward Phase Wave Model, Zainelabideen Yousif Mijbil Jun 2020

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 ...


Generalized Magnetoelectronic Circuit Theory And Spin Relaxation At Interfaces In Magnetic Multilayers, G. G. Baez Flores, Alexey Kovalev, Mark Van Schilfgaarde, K. D. Belashchenko Jun 2020

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, N H. Dung, N B. Doan, P De Rango, L Ranno, Karl G. Sandeman, N M. Dempsey Jun 2020

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 ...


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 Jun 2020

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 ...


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 May 2020

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 ...


D-Orbital Occupancy Of Transition Metal Oxides By X-Ray Absorption Near Edge Structure (Xanes), Eric Kurywczak May 2020

D-Orbital Occupancy Of Transition Metal Oxides By X-Ray Absorption Near Edge Structure (Xanes), Eric Kurywczak

Seton Hall University Dissertations and Theses (ETDs)

XANES L2 and L3-edge X-Ray Absorption Near Edge Spectra (XANES) for 4d and 5d row transition metals (TM) oxides are assumed to be directly reflecting unoccupied d orbitals influenced by the local symmetry of the metal ion. XANES L2- and L3-edge data analysis through non-linear curve fitting allows for a unique, efficient look at the structural eccentricities of transition metal oxides. In this way it is possible to determine the oxidation state of a material as well as its site symmetry. We have used non-linear least-squares fitting across the near-edge region of ...


Pressure Tuning Of Structural And Magnetic Transitions In Euag4as2, Sergey L. Bud’Ko, Li Xiang, Chaowei Hu, Bing Shen, Ni Ni, Paul C. Canfield May 2020

Pressure Tuning Of Structural And Magnetic Transitions In Euag4as2, Sergey L. Bud’Ko, Li Xiang, Chaowei Hu, Bing Shen, Ni Ni, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report temperature-dependent measurements of ambient-pressure specific heat, magnetic susceptibility, anisotropic resistivity, and thermal expansion as well as in-plane resistivity under pressure up to 20.8 kbar on single crystals of EuAg4As2. Based on thermal expansion and in-plane electrical transport measurements at ambient pressure this compound has two, first-order, structural transitions in the 80–120 K temperature range. Ambient-pressure specific heat, magnetization, and thermal expansion measurements show a cascade of up to seven transitions between 8 and 16 K associated with the ordering of the Eu2+ moments. In-plane electrical transport is able to detect the more prominent of these transitions ...


Density Functional Theory Calculations Of Al Doped Hafnia For Different Crystal Symmetry Configurations, Joshua Steier May 2020

Density Functional Theory Calculations Of Al Doped Hafnia For Different Crystal Symmetry Configurations, Joshua Steier

Seton Hall University Dissertations and Theses (ETDs)

Dogan et al.[1], investigated the causes of ferroelectricity in doped hafnia using ab initio methods. Similarly, we investigated the stability of Al doped hafnia using quantum mechanical methods.

There are many different phases of Hafnia: monoclinic, tetragonal, cubic and orthorhombic. Starting with the monoclinic phase of Hafnia, Hafnia undergoes phase transitions which result in different space groups. The temperature at which the tetragonal phase is induced is 2000 K and cubic phase is induced at 2900 K[1]. Different dielectric constants vary from phase to phase. The average dielectric constants are highest for the cubic and tetragonal phases. In ...


Thermophysical Properties And Phase Transformations In Metallic Liquids And Silicate Glasses, Daniel Christian Van Hoesen May 2020

Thermophysical Properties And Phase Transformations In Metallic Liquids And Silicate Glasses, Daniel Christian Van Hoesen

Arts & Sciences Electronic Theses and Dissertations

The first quantitative measurements of the electrical resistivity in binary metallic liquids, used to probe local order in the liquid, are reported in this dissertation. The electrical resistivity is very sensitive to short and medium range ordering because the electron mean free path is approximately the same length scale as the atomic spacing. Particular attention is given to the resistivity value at a crossover temperature that, based on molecular dynamics (MD) simulations, is the onset of cooperative motion in liquid alloys. Experimental evidence for the crossover is found in measurements of the shear viscosity, a dynamical property. An indication of ...


Physics 516: Electromagnetic Phenomena (Spring 2020), Philip C. Nelson May 2020

Physics 516: Electromagnetic Phenomena (Spring 2020), Philip C. Nelson

Department of Physics Papers

These course notes are made publicly available in the hope that they will be useful. All reports of errata will be gratefully received. I will also be glad to hear from anyone who reads them, whether or not you find errors: pcn@upenn.edu.


Impact Of Nematicity On The Relationship Between Antiferromagnetic Fluctuations And Superconductivity In Fese0.91s0.09 Under Pressure, Khusboo Rana, Li Xiang, Paul W. Wiecki, Raquel A. Ribeiro, Guilherme Gorgen Lesseux, Anna E. Böhmer, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa May 2020

Impact Of Nematicity On The Relationship Between Antiferromagnetic Fluctuations And Superconductivity In Fese0.91s0.09 Under Pressure, Khusboo Rana, Li Xiang, Paul W. Wiecki, Raquel A. Ribeiro, Guilherme Gorgen Lesseux, Anna E. Böhmer, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

The sulfur-substituted FeSe system, FeSe1−xSx, provides a versatile platform for studying the relationship among nematicity, antiferromagnetism, and superconductivity. Here, by nuclear magnetic resonance (NMR) and resistivity measurements up to 4.73 GPa on FeSe0.91S0.09, we established the pressure- (p-) temperature (T) phase diagram in which the nematic state is suppressed with pressure showing a nematic quantum phase transition (QPT) around p=0.5GPa, two superconductivity (SC) regions separated by the QPT appear, and antiferromagnetic (AFM) phase emerges above ∼3.3GPa. From the NMR results up to 2.1 GPa, AFM fluctuations are revealed to be characterized by ...


Computational Simulations Of Temperature-Dependent Dynamics In Type Ii Superconductors Using A Material Specific Formulation Of Ginzburg Landau Theory, Aiden Harbick May 2020

Computational Simulations Of Temperature-Dependent Dynamics In Type Ii Superconductors Using A Material Specific Formulation Of Ginzburg Landau Theory, Aiden Harbick

Undergraduate Honors Theses

Superconducting Radio Frequency (SRF) cavities play a fundamental role in particle accelerators. Efficient operation depends on expelling magnetic flux from the cavity, and any residual flux that remains trapped after cooling below the critical temperature can have a significant impact on performance. Experimental evidence suggests that material defects as well as cooling protocols can have a strong impact on subsequent performance. To better understand these phenomena, we use time-dependent Ginzburg-Landau theory implemented as finite-element simulations. We adapt the theory to allow spatial variation of material-specific parameters along with realistic temperature dependencies. We report on numerical experiments for different configurations of ...


Symmetry And Interface Considerations For Interactions On Mos2, Prescott E. Evans May 2020

Symmetry And Interface Considerations For Interactions On Mos2, Prescott E. Evans

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

The critical role of symmetry, in adsorbate-MoS2 interactions, has been demonstrated through a variety of electronic structure, topology, and catalytic studies of MoS2 and MoS2 composites.A combination of density functional theory and experiment exhibiting diiodobenzene isomer dependent adsorption rates highlight frontier orbital symmetry as key to adsorption on MoS2. It is clear that the geometry and symmetry of MoS2 influences the creation and stability of surface defects, that in turn affect catalytic activity and a myriad of other applications. We have shown that surface reactions such the methanol to methoxy reaction can create defects ...


Competing Magnetic Interactions In The Antiferromagnetic Topological Insulator Mnbi2te4, Bing Li, J.-Q. Yan, D. Pajerowski, Elijah Gordon, Ana-Marija Nedic, Y. Sizyuk, Liqin Ke, Peter P. Orth, David Vaknin, Robert J. Mcqueeney Apr 2020

Competing Magnetic Interactions In The Antiferromagnetic Topological Insulator Mnbi2te4, Bing Li, J.-Q. Yan, D. Pajerowski, Elijah Gordon, Ana-Marija Nedic, Y. Sizyuk, Liqin Ke, Peter P. Orth, David Vaknin, Robert J. Mcqueeney

Physics and Astronomy Publications

The antiferromagnetic (AFM) compound MnBi2Te4 is suggested to be the first realization of an AFM topological insulator. We report on inelastic neutron scattering studies of the magnetic interactions in MnBi2Te4 that possess ferromagnetic triangular layers with AFM interlayer coupling. The spin waves display a large spin gap and pairwise exchange interactions within the triangular layer are long ranged and frustrated by large next-nearest neighbor AFM exchange. The degree of frustration suggests proximity to a variety of magnetic phases, potentially including skyrmion phases, which could be accessed in chemically tuned compounds or upon the application of symmetry-breaking fields.


An Analysis Of The Debate Over Creation, Evolution, And The Timeline Of The Universe At An Ecumenical Christian University, Mason Pohlman Apr 2020

An Analysis Of The Debate Over Creation, Evolution, And The Timeline Of The Universe At An Ecumenical Christian University, Mason Pohlman

Honors Theses

Throughout a significant portion of history and within modern culture, the fields of science and religion appear to be competing for the same holds in a person’s belief system. Universities are where academics and the sciences are the prevailing held truth, while in churches, the Bible reigns as supreme authority. However, in a Christian academic setting, the predominate school of thought in belief systems might turn into a little more of a melting pot. By analyzing gathered personal data (via surveys and interviews), one can begin to piece together the predominate thoughts on the apparent conflict between religion and ...


Spin Dynamics In Antiferromagnetic Oxypnictides And Fluoropnictides: Lamnaso, Lamnsbo, And Bamnasf, Farhan Islam, Elijah Gordon, Pinaki Das, Yong Liu, Liquin Ke, Douglas L. Abernathy, Robert L. Mcqueeney, David Vaknin Apr 2020

Spin Dynamics In Antiferromagnetic Oxypnictides And Fluoropnictides: Lamnaso, Lamnsbo, And Bamnasf, Farhan Islam, Elijah Gordon, Pinaki Das, Yong Liu, Liquin Ke, Douglas L. Abernathy, Robert L. Mcqueeney, David Vaknin

Ames Laboratory Accepted Manuscripts

Inelastic neutron scattering (INS) from polycrystalline antiferromagnetic LaMnAsO, LaMnSbO, and BaMnAsF are analyzed using a J(1)-J(2)-J(c) Heisenberg model in the framework of the linear spin-wave theory. All three systems show clear evidence that the nearest- and next-nearest-neighbor interactions within the Mn square lattice layer (J(1) and J(2)) are both antiferromagnetic (AFM). However, for all compounds studied the competing interactions have a ratio of 2J(2)/J(1) < 1, which favors the square lattice checkerboard AFM structure over the stripe AFM structure. The interplane coupling Jc in all three systems is on the order of similar to 3 x 10(-4)J(1), rendering the magnetic properties of these systems with quasi-two-dimensional character. The substitution of Sb for As significantly lowers the in-plane exchange coupling, which is also reflected in the decrease of the Neel temperature, T-N. Although BaMnAsF shares the same MnAs sheets as LaMnAsO, their J(1) and J(2) values are substantially different. Using density functional theory, we calculate exchange parameters J(ij) to rationalize the differences among these systems.


Magnetic Forces In The Absence Of A Classical Magnetic Field, Ismael L. Paiva, Yakir Aharonov, Jeff Tollaksen, Mordecai Waegell Apr 2020

Magnetic Forces In The Absence Of A Classical Magnetic Field, Ismael L. Paiva, Yakir Aharonov, Jeff Tollaksen, Mordecai Waegell

Mathematics, Physics, and Computer Science Faculty Articles and Research

It is shown that, in some cases, the effect of discrete distributions of flux lines in quantum mechanics can be associated with the effect of continuous distributions of magnetic fields with special symmetries. In particular, flux lines with an arbitrary value of magnetic flux can be used to create energetic barriers, which can be used to confine quantum systems in specially designed configurations. This generalizes a previous work where such energy barriers arose from flux lines with half-integer fluxons. Furthermore, it is shown how the Landau levels can be obtained from a two-dimensional grid of flux lines. These results suggest ...


Competing Pairing Interactions Responsible For The Large Upper Critical Field In A Stoichiometric Iron-Based Superconductor Cakfe4as4, Matthew Bristow, William Knafo, Pascal Reiss, William R. Meier, Paul C. Canfield, Stephen J. Blundell, Amalia I. Coldea Apr 2020

Competing Pairing Interactions Responsible For The Large Upper Critical Field In A Stoichiometric Iron-Based Superconductor Cakfe4as4, Matthew Bristow, William Knafo, Pascal Reiss, William R. Meier, Paul C. Canfield, Stephen J. Blundell, Amalia I. Coldea

Physics and Astronomy Publications

The upper critical field of multiband superconductors is an important quantity that can reveal details about the nature of the superconducting pairing. Here we experimentally map out the complete upper-critical-field phase diagram of a stoichiometric superconductor, CaKFe4As4, up to 90T for different orientations of the magnetic field and at temperatures down to 4.2K. The upper critical fields are extremely large, reaching values close to ∼3Tc at the lowest temperature, and the anisotropy decreases dramatically with temperature, leading to essentially isotropic superconductivity at 4.2K. We find that the temperature dependence of the upper critical field can be well described ...