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Iowa State University

2017

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Articles 1 - 30 of 105

Full-Text Articles in Physics

Texture Development And Coercivity Enhancement In Cast Alnico 9 Magnets, Wenyong Zhang, Shah Valloppilly, Xingzhong Li, Lanping Yue, Ralph Skomski, Iver E. Anderson, Matthew J. Kramer, Wei Tang, Jeff Shield, David J. Sellmyer Dec 2017

Texture Development And Coercivity Enhancement In Cast Alnico 9 Magnets, Wenyong Zhang, Shah Valloppilly, Xingzhong Li, Lanping Yue, Ralph Skomski, Iver E. Anderson, Matthew J. Kramer, Wei Tang, Jeff Shield, David J. Sellmyer

Ames Laboratory Accepted Manuscripts

The effect of Y addition and magnetic field on texture and magnetic properties of arc-melted alnico 9 magnets has been investigated. Small additions of Y (1.5 wt.%) develop a (200) texture for the arc-melted alnico 9 magnet. Such a texture is hard to form in cast samples. To achieve this goal, we set up a high-field annealing system with a maximum operation temperature of 1250 °C. This system enabled annealing in a field of 45 kOe with subsequent draw annealing for the solutionized buttons; we have been able to substantially increase remanence ratio and coercivity, from 0.70 and ...


Emergent Ising Degrees Of Freedom Above A Double-Stripe Magnetic Ground State, Guanghua Zhang, Rebecca Flint Dec 2017

Emergent Ising Degrees Of Freedom Above A Double-Stripe Magnetic Ground State, Guanghua Zhang, Rebecca Flint

Ames Laboratory Accepted Manuscripts

Double-stripe magnetism [ Q = ( π / 2 , π / 2 ) ] has been proposed as the magnetic ground state for both the iron-telluride and BaTi 2 Sb 2 O families of superconductors. Double-stripe order is captured within a J 1 − J 2 − J 3 Heisenberg model in the regime J 3 ≫ J 2 ≫ J 1 . Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector ( π , π ) . Because the ground state is fourfold ...


Influence Of Classical Anisotropy Fields On The Properties Of Heisenberg Antiferromagnets Within Unified Molecular Field Theory, David C. Johnston Dec 2017

Influence Of Classical Anisotropy Fields On The Properties Of Heisenberg Antiferromagnets Within Unified Molecular Field Theory, David C. Johnston

Ames Laboratory Accepted Manuscripts

A comprehensive study of the influence of classical anisotropy fields on the magnetic properties of Heisenberg antiferromagnets within unified molecular field theory versus temperature T , magnetic field H , and anisotropy field parameter h A 1 is presented for systems comprised of identical crystallographically-equivalent local moments. The anisotropy field for collinear z -axis antiferromagnetic (AFM) ordering is constructed so that it is aligned in the direction of each ordered and/or field-induced thermal-average moment with a magnitude proportional to the moment, whereas that for XY anisotropy is defined to be in the direction of the projection of the moment onto the ...


R14(Au, M)51 (R = Y, La−Nd, Sm−Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, In,Sn, Sb, Bi): Stability Ranges And Site Preference In The Gd14ag51 Structure Type, Chris Celania, Volodymyr Smetana, Alessia Provino, Pietro Manfrinetti, Anja-Verena Mudring Dec 2017

R14(Au, M)51 (R = Y, La−Nd, Sm−Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, In,Sn, Sb, Bi): Stability Ranges And Site Preference In The Gd14ag51 Structure Type, Chris Celania, Volodymyr Smetana, Alessia Provino, Pietro Manfrinetti, Anja-Verena Mudring

Ames Laboratory Accepted Manuscripts

Twenty new ternary representatives of the Gd14Ag51 structure type have been synthesized within the R-Au-M family (R = Y, La–Nd, Sm–Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, In, Sn, Sb, Bi) using solid state synthesis techniques. The list of post transition metals (M) involved in the formation of this type of structure could be augmented by five new representatives. All compounds crystallize in the hexagonal space group P6/m (#175) with the unit cell ranges of a = 12.3136(2)–12.918(1) Å and c = 8.9967(3)–9.385(1) Å, and incorporate different ...


Local Nematic Susceptibility In Stressed Bafe 2 As 2 From Nmr Electric Field Gradient Measurements, T. Kissikov, R. Sarkar, M. Lawson, B. T. Bush, Erik I. Timmons, Makariy A. Tanatar, Ruslan Prozorov, S. L. Bud’Ko, Paul C. Canfield, R. M. Fernandes, W. F. Goh, W. E. Pickett, N. J. Curro Dec 2017

Local Nematic Susceptibility In Stressed Bafe 2 As 2 From Nmr Electric Field Gradient Measurements, T. Kissikov, R. Sarkar, M. Lawson, B. T. Bush, Erik I. Timmons, Makariy A. Tanatar, Ruslan Prozorov, S. L. Bud’Ko, Paul C. Canfield, R. M. Fernandes, W. F. Goh, W. E. Pickett, N. J. Curro

Ames Laboratory Accepted Manuscripts

The electric field gradient (EFG) tensor at the 75As site couples to the orbital occupations of the As porbitals and is a sensitive probe of local nematicity in BaFe2As2. We use nuclear magnetic resonance to measure the nuclear quadrupolar splittings and find that the EFG asymmetry responds linearly to the presence of a strain field in the paramagnetic phase. We extract the nematic susceptibility from the slope of this linear response as a function of temperature and find that it diverges near the structural transition, in agreement with other measures of the bulk nematic susceptibility. Our work establishes an alternative ...


Nematicity, Magnetism And Superconductivity In Fese, Anna E. Böhmer, Andreas Kreisel Dec 2017

Nematicity, Magnetism And Superconductivity In Fese, Anna E. Böhmer, Andreas Kreisel

Ames Laboratory Accepted Manuscripts

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these ...


Diffusion Of Two-Dimensional Epitaxial Clusters On Metal (100) Surfaces: Facile Versus Nucleation-Mediated Behavior And Their Merging For Larger Sizes, King C. Lai, Da-Jiang Liu, James W. Evans Dec 2017

Diffusion Of Two-Dimensional Epitaxial Clusters On Metal (100) Surfaces: Facile Versus Nucleation-Mediated Behavior And Their Merging For Larger Sizes, King C. Lai, Da-Jiang Liu, James W. Evans

Ames Laboratory Accepted Manuscripts

For diffusion of two-dimensional homoepitaxial clusters of N atoms on metal (100) surfaces mediated by edge atom hopping, macroscale continuum theory suggests that the diffusion coefficient scales like DN∼N−β with β=3/2. However, we find quite different and diverse behavior in multiple size regimes. These include: (i) facile diffusion for small sizes N<9; (ii) slow nucleation-mediated diffusion with small β<1 for “perfect” sizes N=Np=L2 or L(L+1), for L=3,4, ... having unique ground-state shapes, for moderate sizes 9≤N≤O(102); the same also applies for N=Np+3, Np+4, ...(iii) facile diffusion but with large β>2 for N=Np+1 and Np+2 also for moderate sizes 9≤N≤O(102); (iv) merging of the above distinct branches and subsequent anomalous scaling with 1≲β<3/2, reflecting the quasifacetted structure of clusters, for larger N=O(102) to N=O(103); (v) classic scaling with β=3/2 for very large N=O(103) and above. The specified size ranges apply for typical model parameters. We focus on the moderate size regime where we show that diffusivity cycles quasiperiodically from the slowest branch for Np+3 (not Np) to the fastest branch for Np+1. Behavior is quantified by kinetic Monte Carlo simulation of an appropriate stochastic lattice-gas model. However, precise analysis must account for a strong enhancement of diffusivity for short time increments due to back correlation in the cluster motion. Further understanding of this enhancement, of anomalous size scaling behavior, and of the merging of various branches, is facilitated by combinatorial analysis of the number of the ground-state and low-lying excited state cluster configurations, and also of kink populations.


First-Principles Study On The Electronic, Optical, And Transport Properties Of Monolayer Α- And Β-Gese, Yuanfeng Xu, Hao Zhang, Hezhu Shao, Gang Ni, Jing Li, Hongliang Lu, Rongjun Zhang, Bo Peng, Yongyuan Zhu, Heyuan Zhu, Costas M. Soukoulis Dec 2017

First-Principles Study On The Electronic, Optical, And Transport Properties Of Monolayer Α- And Β-Gese, Yuanfeng Xu, Hao Zhang, Hezhu Shao, Gang Ni, Jing Li, Hongliang Lu, Rongjun Zhang, Bo Peng, Yongyuan Zhu, Heyuan Zhu, Costas M. Soukoulis

Ames Laboratory Accepted Manuscripts

The extraordinary properties and the novel applications of black phosphorene induce the research interest in the monolayer group-IV monochalcogenides. Here using first-principles calculations, we systematically investigate the electronic, transport, and optical properties of monolayer alpha- and beta-GeSe, revealing a direct band gap of 1.61 eV for monolayer alpha-GeSe and an indirect band gap of 2.47 eV for monolayer beta-GeSe. For monolayer beta-GeSe, the electronic/hole transport is anisotropic, with an extremely high electron mobility of 2.93 x 10(4) cm(2)/Vs along the armchair direction, comparable to that of black phosphorene. Furthermore, for beta-GeSe, robust band ...


Ionic Depletion At The Crystalline Gibbs Layer Of Peg-Capped Gold Nanoparticle Brushes At Aqueous Surfaces, Wenjie Wang, Honghu Zhang, Surya Mallapragada, Alex Travesset, David Vaknin Dec 2017

Ionic Depletion At The Crystalline Gibbs Layer Of Peg-Capped Gold Nanoparticle Brushes At Aqueous Surfaces, Wenjie Wang, Honghu Zhang, Surya Mallapragada, Alex Travesset, David Vaknin

Ames Laboratory Accepted Manuscripts

In situ surface-sensitive x-ray diffraction and grazing incidence x-ray fluorescence spectroscopy (GIXFS) methods are combined to determine the ionic distributions across the liquid/vapor interfaces of thiolated-polyethylene-glycol–capped gold nanoparticle (PEG-AuNP) solutions. Induced by the addition of salts (i.e., Cs2SO4) to PEG-AuNPs solutions, two-dimensional hexagonal lattices of PEG-AuNPs form spontaneously at the aqueous surfaces, as is demonstrated by x-ray reflectivity and grazing incidence small-angle x-ray scattering. By taking advantage of element specificity with the GIXFS method, we find that the cation Cs+ concentration at the crystalline film is significantly reduced in parts of the PEG-AuNP film compared with that ...


A Molecular Debye-Hückel Theory Of Solvation In Polar Fluids: An Extension Of The Born Model, Tiejun Xiao, Xueyu Song Dec 2017

A Molecular Debye-Hückel Theory Of Solvation In Polar Fluids: An Extension Of The Born Model, Tiejun Xiao, Xueyu Song

Ames Laboratory Accepted Manuscripts

A dielectric response theory of solvation beyond the conventional Born model for polar fluids is presented. The dielectric response of a polar fluid is described by a Born response mode and a linear combination of Debye-Hückel-like response modes that capture the nonlocal response of polar fluids. The Born mode is characterized by a bulk dielectric constant, while a Debye-Hückel mode is characterized by its corresponding Debye screening length. Both the bulk dielectric constant and the Debye screening lengths are determined from the bulk dielectric function of the polar fluid. The linear combination coefficients of the response modes are evaluated in ...


Measurements Of Azimuthal Anisotropy And Charged-Particle Multiplicity In D + Au Collisions At √Snn = 200, 62.4, 39, And 19.6 Gev, C. Aidala, Nicole J. Apadula, Nels J. Hotvedt, John G. Lajoie, Alexandre Lebedev, S. H. Lee, Craig Ogilvie, Milap R. Patel, Timothy T. Rinn, Marzia Rosati, Jonathan C. Runchey, Abhisek Sen, M. Shimomura, Arbin Timilsina, Et Al., Phenix Collaboration Dec 2017

Measurements Of Azimuthal Anisotropy And Charged-Particle Multiplicity In D + Au Collisions At √Snn = 200, 62.4, 39, And 19.6 Gev, C. Aidala, Nicole J. Apadula, Nels J. Hotvedt, John G. Lajoie, Alexandre Lebedev, S. H. Lee, Craig Ogilvie, Milap R. Patel, Timothy T. Rinn, Marzia Rosati, Jonathan C. Runchey, Abhisek Sen, M. Shimomura, Arbin Timilsina, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present measurements of the elliptic flow (v(2)) as a function of transverse momentum (p(T)), pseudorapidity (eta), and centrality in d + Au collisions at root s(NN) = 200, 62.4, 39, and 19.6 GeV. The beam-energy scan of d + Au collisions provides a testing ground for the onset of flow signatures in small collision systems. We measure a nonzero v(2) signal at all four collision energies, which, at midrapidity and low p(T), is consistent with predictions from viscous hydrodynamic models. Comparisons with calculations from parton transport models (based on the AMPT Monte Carlo generator) show ...


B-Meson Production At Forward And Backward Rapidity In P+P And Cu+Au Collisions At √Snn=200 Gev, C. Aidala, Nicole J. Apadula, John C. Hill, Nels J. Hotvedt, Todd Kempel, John G. Lajoie, Alexandre Lebedev, S. H. Lee, Craig Ogilvie, Milap R. Patel, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Jonathan C. Runchey, Abhisek Sen, Alex Shaver, M. Shimomura, Arbin Timilsina, Shawn Whitaker, Et Al., Phenix Collaboration Dec 2017

B-Meson Production At Forward And Backward Rapidity In P+P And Cu+Au Collisions At √Snn=200 Gev, C. Aidala, Nicole J. Apadula, John C. Hill, Nels J. Hotvedt, Todd Kempel, John G. Lajoie, Alexandre Lebedev, S. H. Lee, Craig Ogilvie, Milap R. Patel, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Jonathan C. Runchey, Abhisek Sen, Alex Shaver, M. Shimomura, Arbin Timilsina, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The fraction of J/psi mesons which come from B-meson decay, F-B -> J/psi is measured for J/psi rapidity 1.2 < |y| < 2.2 and p(T) > 0 in p + p and Cu+Au collisions at root s(NN) = 200 GeV with the PHENIX detector. The extracted fraction is F-B -> J/psi = 0.025 +/- 0.006 (stat) +/- 0.010(syst) for p + p collisions. For Cu+Au collisions, F-B -> J/psi is 0.094 +/- 0.028(stat) +/- 0.037(syst) in the Au-going direction (-2.2 < y < -1.2) and 0.089 +/- 0.026(stat) +/- 0.040(syst) in the Cu-going direction (1.2 < y < 2.2). The nuclear modification factor, R-CuAu,of B mesons in Cu+Au collisions is consistent with binary scaling of measured yields in p + p at both forward and backward rapidity.


Optical Absorption Properties Of Ge2–44 And P-Doped Ge Nanoparticles, Wei Qin, Wen-Cai Lu, Li-Zhen Zhao, Kai-Ming Ho, Cai-Zhuang Wang Dec 2017

Optical Absorption Properties Of Ge2–44 And P-Doped Ge Nanoparticles, Wei Qin, Wen-Cai Lu, Li-Zhen Zhao, Kai-Ming Ho, Cai-Zhuang Wang

Ames Laboratory Accepted Manuscripts

The optical absorption properties of non-crystalline and crystalline Ge nanoparticles with the sizes from ∼2.5 to 15 Å have been studied at the B3LYP/6-31G level using time-dependent density functional theory. Hydrogen passivation and phosphorus doping on some selected Ge nanoparticles were also calculated. With the increase of cluster size, the optical absorption spectra of the non-crystalline Ge nanoparticles change from many peaks to a continuous broad band and at the same time exhibit a systematic red-shift. Doping phosphorus also causes the absorption spectra to shift toward the lower energy region for both non-crystalline and crystalline Ge nanoparticles. The ...


Nmr Study Of The New Magnetic Superconductor Cak ( Fe 0.951 Ni 0.049 ) 4 As 4 : Microscopic Coexistence Of The Hedgehog Spin-Vortex Crystal And Superconductivity, Qing-Ping Ding, William R. Meier, A. E. Böhmer, S. L. Bud’Ko, Paul C. Canfield, Yuji Furukawa Dec 2017

Nmr Study Of The New Magnetic Superconductor Cak ( Fe 0.951 Ni 0.049 ) 4 As 4 : Microscopic Coexistence Of The Hedgehog Spin-Vortex Crystal And Superconductivity, Qing-Ping Ding, William R. Meier, A. E. Böhmer, S. L. Bud’Ko, Paul C. Canfield, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

The coexistence of a new-type antiferromagnetic (AFM) state, the so-called hedgehog spin-vortex crystal (SVC), and superconductivity (SC) is evidenced by an 75 As nuclear magnetic resonance study on single-crystalline CaK ( Fe 0.951 Ni 0.049 ) 4 As 4 . The hedgehog SVC order is clearly demonstrated by the direct observation of internal magnetic induction along the c axis at the As1 site (close to K) and a zero net internal magnetic induction at the As2 site (close to Ca) below an AFM ordering temperature T N ∼ 52 K. The nuclear spin-lattice relaxation rate 1 / T 1 shows a distinct decrease ...


Communication: Diverse Nanoscale Cluster Dynamics: Diffusion Of 2d Epitaxial Clusters, King C. Lai, James W. Evans, Da-Jiang Liu Nov 2017

Communication: Diverse Nanoscale Cluster Dynamics: Diffusion Of 2d Epitaxial Clusters, King C. Lai, James W. Evans, Da-Jiang Liu

Ames Laboratory Accepted Manuscripts

The dynamics of nanoscale clusters can be distinct from macroscale behavior described by continuum formalisms. For diffusion of 2D clusters of N atoms in homoepitaxial systems mediated by edge atom hopping, macroscale theory predicts simple monotonic size scaling of the diffusion coefficient, DN ∼ N−β, with β = 3/2. However, modeling for nanoclusters on metal(100) surfaces reveals that slow nucleation-mediated diffusion displaying weak size scaling β < 1 occurs for “perfect” sizes Np = L2 and L(L+1) for integer L = 3,4,… (with unique square or near-square ground state shapes), and also for Np+3, Np+4,…. In contrast, fast facile nucleation-free diffusion displaying strong size scaling β ≈ 2.5 occurs for sizes Np+1 and Np+2. DN versus N oscillates strongly between the slowest branch (for Np+3) and the fastest branch (for Np+1). All branches merge for N = O(102), but macroscale behavior is only achieved for much larger N = O(103). This analysis reveals the unprecedented diversity of behavior on the nanoscale.


In Situ Investigation Of Magnetism In Metastable Phases Of Levitated Fe83b17 During Solidification, D. G. Quirinale, D. Messina, G. E. Rustan, Andreas Kreyssig, Ruslan Prozorov, Alan I. Goldman Nov 2017

In Situ Investigation Of Magnetism In Metastable Phases Of Levitated Fe83b17 During Solidification, D. G. Quirinale, D. Messina, G. E. Rustan, Andreas Kreyssig, Ruslan Prozorov, Alan I. Goldman

Ames Laboratory Accepted Manuscripts

In situ measurements of structure, density, and magnetization on samples of Fe83B17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe23B6/ fcc Fe coherently grown structures and primitive tetragonal Fe3B metastable phase in addition to characterizing the equilibrium Fe2B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperature metastable structures.


Thickness-Dependent Energetics For Pb Adatoms On Low-Index Pb Nanofilm Surfaces: First-Principles Calculations, Wei Li, Li Huang, Raj Ganesh S. Pala, Guang-Hong Lu, Feng Liu, James W. Evans, Yong Han Nov 2017

Thickness-Dependent Energetics For Pb Adatoms On Low-Index Pb Nanofilm Surfaces: First-Principles Calculations, Wei Li, Li Huang, Raj Ganesh S. Pala, Guang-Hong Lu, Feng Liu, James W. Evans, Yong Han

Physics and Astronomy Publications

Adsorption, interaction, and diffusion of adatoms on surfaces control growth and relaxation of epitaxial nanostructures and nanofilms. Previous reports of key diffusion barriers for Pb diffusion on low-index Pb surfaces are limited in scope and accuracy. Thus, we apply density functional theory (DFT) to calculate the adsorption and diffusion energetics for a Pb adatom on Pb(111), Pb(100), and Pb(110) nanofilms with different thicknesses. We find that these quantities exhibit damped oscillatory variation with increasing film thickness. For Pb(111) films, energetics along the minimum energy path for Pb adatom diffusion between adjacent fcc and hcp sites varies ...


Emergent Bloch Excitations In Mott Matter, Nicola Lanatà, Tsung-Han Lee, Yong-Xin Yao, Vladimir Dobrosavljević Nov 2017

Emergent Bloch Excitations In Mott Matter, Nicola Lanatà, Tsung-Han Lee, Yong-Xin Yao, Vladimir Dobrosavljević

Ames Laboratory Accepted Manuscripts

We develop a unified theoretical picture for excitations in Mott systems, portraying both the heavy quasiparticle excitations and the Hubbard bands as features of an emergent Fermi liquid state formed in an extended Hilbert space, which is nonperturbatively connected to the physical system. This observation sheds light on the fact that even the incoherent excitations in strongly correlated matter often display a well-defined Bloch character, with pronounced momentum dispersion. Furthermore, it indicates that the Mott point can be viewed as a topological transition, where the number of distinct dispersing bands displays a sudden change at the critical point. Our results ...


Phase Transitions In Mgsio3 Post-Perovskite In Super-Earth Mantles, Koichiro Umemoto, Renata M. Wentzcovitch, Shunqing Wu, Min Ji, Cai-Zhuang Wang, Kai-Ming Ho Nov 2017

Phase Transitions In Mgsio3 Post-Perovskite In Super-Earth Mantles, Koichiro Umemoto, Renata M. Wentzcovitch, Shunqing Wu, Min Ji, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

The highest pressure form of the major Earth-forming mantle silicate is MgSiO3 post-perovskite (PPv). Understanding the fate of PPv at TPa pressures is the first step for understanding the mineralogy of super-Earths-type exoplanets, arguably the most interesting for their similarities with Earth. Modeling their internal structure requires knowledge of stable mineral phases, their properties under compression, and major element abundances. Several studies of PPv under extreme pressures support the notion that a sequence of pressure induced dissociation transitions produce the elementary oxides SiO2 and MgO as the ultimate aggregation form at ∼3 TPa. However, none of these studies have addressed ...


Broadband Mixing Of Pt-Symmetric And Pt-Broken Phases In Photonic Heterostructures With A One-Dimensional Loss/Gain Bilayer, Ege Özgün, Andriy E. Serebryannikov, Ekmel Ozbay, Costas M. Soukoulis Nov 2017

Broadband Mixing Of Pt-Symmetric And Pt-Broken Phases In Photonic Heterostructures With A One-Dimensional Loss/Gain Bilayer, Ege Özgün, Andriy E. Serebryannikov, Ekmel Ozbay, Costas M. Soukoulis

Ames Laboratory Accepted Manuscripts

Combining loss and gain components in one photonic heterostructure opens a new route to efficient manipulation by radiation, transmission, absorption, and scattering of electromagnetic waves. Therefore, loss/gain structures enabling PT-symmetric and PT-broken phases for eigenvalues have extensively been studied in the last decade. In particular, translation from one phase to another, which occurs at the critical point in the two-channel structures with one-dimensionalloss/gain components, is often associated with one-way transmission. In this report, broadband mixing of the PT-symmetric and PT-broken phases for eigenvalues is theoretically demonstrated in heterostructures with four channels obtained by combining a one-dimensional loss/gain ...


Electromagnetic Shielding Effectiveness Of 3d Printed Polymer Composites, Z. Viskadourakis, K. C. Vasilopoulos, E. N. Economou, Costas M. Soukoulis, G. Kenanakis Nov 2017

Electromagnetic Shielding Effectiveness Of 3d Printed Polymer Composites, Z. Viskadourakis, K. C. Vasilopoulos, E. N. Economou, Costas M. Soukoulis, G. Kenanakis

Ames Laboratory Accepted Manuscripts

We report on preliminary results regarding the electromagnetic shielding effectiveness of various 3D printed polymeric composite structures. All studied samples were fabricated using 3D printing technology, following the fused deposition modeling approach, using commercially available filaments as starting materials. The electromagnetic shielding performance of the fabricated 3D samples was investigated in the so called C-band of the electromagnetic spectrum (3.5–7.0 GHz), which is typically used for long-distance radio telecommunications. We provide evidence that 3D printing technology can be effectively utilized to prepare operational shields, making them promising candidates for electromagnetic shielding applications for electronic devices.


Coexistence Of Type-Ii Dirac Point And Weak Topological Phase In Pt 3 Sn, Minsung Kim, Cai-Zhuang Wang, Kai-Ming Ho Nov 2017

Coexistence Of Type-Ii Dirac Point And Weak Topological Phase In Pt 3 Sn, Minsung Kim, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

Intriguing topological phases may appear in both insulating and semimetallic states. Topological insulators exhibit topologically nontrivial band inversion, while topological Dirac/Weyl semimetals show “relativistic” linear band crossings. Here, we report an unusual topological state of Pt3Sn, where the two topological features appear simultaneously. Based on first-principles calculations, we show that Pt3Sn is a three-dimensional weak topological semimetal with topologically nontrivial band inversion between the valence and conduction bands, where the band structure also possesses type-II Dirac points at the boundary of two electron pockets. The formation of the Dirac points can be understood in terms of the representations of ...


Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney Nov 2017

Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

Low temperature powder inelastic neutron scattering measurements were performed on three different powder samples; parent BaMn2As2,12.5% K-doped Ba0.875K0.125Mn2As2 and 25% K-doped Ba(0.75)K0.25Mn2As2. The Heisenberg Model involving J1‐J2‐Jz coupling constants were compared to the data by a powder integration routine using Monte Carlo integration methods. The best magnetic parameters were selected using a chi-square test where model intensities were compared to the full (q,E) dependence of magnetic scattering. A key step to this analysis is the characterization of the background which is formed mostly by phonon scattering intensities along with ...


Subsurface Bending And Reorientation Of Tilted Vortex Lattices In Bulk Isotropic Superconductors Due To Coulomb-Like Repulsion At The Surface, E. Herrera, I. Guillamon, J. A. Galvis, A. Correa, A. Fente, S. Vieira, H. Suderow, A. Yu. Martynovich, Vladimir G. Kogan Nov 2017

Subsurface Bending And Reorientation Of Tilted Vortex Lattices In Bulk Isotropic Superconductors Due To Coulomb-Like Repulsion At The Surface, E. Herrera, I. Guillamon, J. A. Galvis, A. Correa, A. Fente, S. Vieira, H. Suderow, A. Yu. Martynovich, Vladimir G. Kogan

Ames Laboratory Accepted Manuscripts

We study vortex lattices (VLs) in superconducting weak-pinning platelet-like single crystals of β−Bi2Pdin tilted magnetic fields with a scanning tunneling microscope. We show that vortices exit the sample perpendicular to the surface and are thus bent beneath the surface. The structure and orientation of the tilted VLs in the bulk are, for large tilt angles, strongly affected by Coulomb-type intervortex repulsion at the surface due to stray magnetic fields.


Electromagnetic Fields From Quantum Sources In Heavy-Ion Collisions, Balthazar Peroutka, Kirill Tuchin Nov 2017

Electromagnetic Fields From Quantum Sources In Heavy-Ion Collisions, Balthazar Peroutka, Kirill Tuchin

Physics and Astronomy Publications

We compute the electromagnetic field created by an ultrarelativistic charged particle in vacuum at distances comparable to the particle Compton wavelength. The wave function of the particle is governed by the Klein-Gordon equation, for a scalar particle, or the Dirac equation, for a spin-half particle. The produced electromagnetic field is essentially different in magnitude and direction from the Coulomb field, induced by a classical point charge, due to the quantum diffusion effect. Thus, a realistic computation of the electromagnetic field produced in heavy-ion collisions must be based upon the full quantum treatment of the valence quarks.


Collapsed Tetragonal Phase Transition In Laru2p2, Gil Drachuck, Aashish Sapkota, Wageesha T. Jayasekara, Karunakar Kothapalli, Sergey L. Bud’Ko, Alan I. Goldman, Andreas Kreyssig, Paul C. Canfield Nov 2017

Collapsed Tetragonal Phase Transition In Laru2p2, Gil Drachuck, Aashish Sapkota, Wageesha T. Jayasekara, Karunakar Kothapalli, Sergey L. Bud’Ko, Alan I. Goldman, Andreas Kreyssig, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

The structural properties of LaRu2P2 under external pressure have been studied up to 14 GPa, employing high-energy x-ray diffraction in a diamond-anvil pressure cell. At ambient conditions, LaRu2P2 (I4/mmm) has a tetragonal structure with a bulk modulus of B=105(2) GPa and exhibits superconductivity at Tc=4.1 K. With the application of pressure, LaRu2P2 undergoes a phase transition to a collapsed tetragonal (cT) state with a bulk modulus of B=175(5) GPa. At the transition, the c-lattice parameter exhibits a sharp decrease with a concurrent increase of the a-lattice parameter. The cT phase transition in ...


Doping Evolution Of The Anisotropic Upper Critical Fields In The Iron-Based Superconductor Ba1−Xkxfe2as2, Makariy A. Tanatar, Yong Liu, J. Jaroszynski,, J. S. Brooks, Thomas A. Lograsso, Ruslan Prozorov Nov 2017

Doping Evolution Of The Anisotropic Upper Critical Fields In The Iron-Based Superconductor Ba1−Xkxfe2as2, Makariy A. Tanatar, Yong Liu, J. Jaroszynski,, J. S. Brooks, Thomas A. Lograsso, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

In-plane resistivity measurements as a function of temperature and magnetic field up to 35 T with precise orientation within the crystallographic ac plane were used to study the upper critical field Hc2 of the hole-doped iron-based superconductor Ba1−xKxFe2As2. Compositions of the samples studied spanned from under- doped x=0.17 (Tc=12 K) and x=0.22 (Tc=20 K), both in the coexistence range of stripe magnetism and superconductivity, through optimal doping x=0.39 (Tc=38.4 K) and x=0.47 (Tc=37.2 K), to overdoped x=0.65 (Tc=22 K) and x=0 ...


Determining The Vortex Tilt Relative To A Superconductor Surface, Vladimir G. Kogan, J. R. Kirtley Nov 2017

Determining The Vortex Tilt Relative To A Superconductor Surface, Vladimir G. Kogan, J. R. Kirtley

Ames Laboratory Accepted Manuscripts

It is of interest to determine the exit angle of a vortex from a superconductor surface, since this affects the intervortex interactions and their consequences. Two ways to determine this angle are to image the vortex magnetic fields above the surface, or the vortex core shape at the surface. In this work we evaluate the field h(x,y,z) above a flat superconducting surface x,y and the currents J(x,y) at that surface for a straight vortex tilted relative to the normal to the surface, for both the isotropic and anisotropic cases. In principle, these results can ...


Electronic, Magnetic, And Magnetocrystalline Anisotropy Properties Of Light Lanthanides, T. A. Hackett, D. J. Baldwin, Durga Paudyal Nov 2017

Electronic, Magnetic, And Magnetocrystalline Anisotropy Properties Of Light Lanthanides, T. A. Hackett, D. J. Baldwin, Durga Paudyal

Ames Laboratory Accepted Manuscripts

Theoretical understanding of interactions between localized and mobile electrons and the crystal environment in light lanthanides is important because of their key role in much needed magnetic anisotropy in permanent magnet materials that have a great impact in automobile and wind turbine applications. We report electronic, magnetic, and magnetocrystalline properties of these basic light lanthanide elements studied from advanced density functional theory (DFT) calculations. We find that the inclusion of onsite 4f electron correlation and spin orbit coupling within the full-potential band structure is needed to understand the unique magnetocrystalline properties of these light lanthanides. The onsite electron correlation, spin ...


Reorientations, Relaxations, Metastabilities, And Multidomains Of Skyrmion Lattices, L. J. Bannenberg, F. Qian, R. M. Dalgliesh, N. Martin, G. Chaboussant, M. Schmidt, Deborah L. Schlagel, Thomas A. Lograsso, Diamond Light Source Ltd., C. Pappas Nov 2017

Reorientations, Relaxations, Metastabilities, And Multidomains Of Skyrmion Lattices, L. J. Bannenberg, F. Qian, R. M. Dalgliesh, N. Martin, G. Chaboussant, M. Schmidt, Deborah L. Schlagel, Thomas A. Lograsso, Diamond Light Source Ltd., C. Pappas

Ames Laboratory Accepted Manuscripts

Magnetic skyrmions are nanosized topologically protected spin textures with particlelike properties. They can form lattices perpendicular to the magnetic field, and the orientation of these skyrmion lattices with respect to the crystallographic lattice is governed by spin-orbit coupling. By performing small-angle neutron scattering measurements, we investigate the coupling between the crystallographic and skyrmion lattices in both Cu2OSeO3 and the archetype chiral magnet MnSi. The results reveal that the orientation of the skyrmion lattice is primarily determined by the magnetic field direction with respect to the crystallographic lattice. In addition, it is also influenced by the magnetic history of the sample ...