Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Iowa State University

2015

Discipline
Keyword
Publication
Publication Type

Articles 1 - 30 of 73

Full-Text Articles in Physics

C60-Induced Devil's Staircase Transformation On A Pb/Si(111) Wetting Layer, Lin-Lin Wang, Duane D. Johnson, Michael C. Tringides Dec 2015

C60-Induced Devil's Staircase Transformation On A Pb/Si(111) Wetting Layer, Lin-Lin Wang, Duane D. Johnson, Michael C. Tringides

Ames Laboratory Publications

Density functional theory is used to study structural energetics of Pb vacancy cluster formation on C60/Pb/Si(111) to explain the unusually fast and error-free transformations between the “Devil's Staircase” (DS) phases on the Pb/Si(111) wetting layer at low temperature (∼110K). The formation energies of vacancy clusters are calculated in C60/Pb/Si(111) as Pb atoms are progressively ejected from the initial dense Pb wetting layer. Vacancy clusters larger than five Pb atoms are found to be stable with seven being the most stable, while vacancy clusters smaller than five are highly unstable, which agrees ...


Imprinting Bulk Amorphous Alloy At Room Temperature, Song-Yi Kim, Eun-Soo Park, Ryan T. Ott, T. A. Lograsso, Moo-Young Huh, Do-Hyang Kim, Jürgen Eckert, Min-Ha Lee Nov 2015

Imprinting Bulk Amorphous Alloy At Room Temperature, Song-Yi Kim, Eun-Soo Park, Ryan T. Ott, T. A. Lograsso, Moo-Young Huh, Do-Hyang Kim, Jürgen Eckert, Min-Ha Lee

Ames Laboratory Publications

We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability ...


Influence Of Mn Concentration On Magnetic Topological Insulator Mnxbi2−Xte3 Thin-Film Hall-Effect Sensor, Ravi L. Hadimani, S. Gupta, S. M. Harstad, Vitalij K. Pecharsky, David C. Jiles Nov 2015

Influence Of Mn Concentration On Magnetic Topological Insulator Mnxbi2−Xte3 Thin-Film Hall-Effect Sensor, Ravi L. Hadimani, S. Gupta, S. M. Harstad, Vitalij K. Pecharsky, David C. Jiles

Ames Laboratory Publications

Hall-effect (HE) sensors based on high-quality Mn-doped Bi2Te3 topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi2Te3. The sensors with low Mn concentrations, MnxBi2-xTe3, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almost eight times as high as ...


Unoccupied Electronic Structure Of Ni2mnga Ferromagnetic Shape Memory Alloy, M. Maniraj, S. W. D′Souza, Abhishek Rai, Deborah L. Schlagel, Thomas A. Lograsso, Aparna Chakrabarti, S. R. Barman Nov 2015

Unoccupied Electronic Structure Of Ni2mnga Ferromagnetic Shape Memory Alloy, M. Maniraj, S. W. D′Souza, Abhishek Rai, Deborah L. Schlagel, Thomas A. Lograsso, Aparna Chakrabarti, S. R. Barman

Ames Laboratory Publications

Momentum resolved inverse photoemission spectroscopy measurements show that the dispersion of the unoccupied bands of Ni2MnGa is significant in the austenite phase. In the martensite phase, it is markedly reduced, which is possibly related to the structural transition to an incommensurate modulated state in the martensite phase. Based on the first principle calculations of the electronic structure of Ni–Mn–Ga, we show that the modification of the spectral shape with surface composition is related to change in the hybridization between the Mn 3d and Ni 3d-like states that dominate the unoccupied conduction band.


Phi Meson Production In D Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole J. Apadula, Alan Dion, John C. Hill, Nels J. Hotvedt, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Timothy T. Rinn, Marzia Rosati, M. Shimomura, C. L. Silva, Arbin Timilsina, Feng Wei, Et Al., Phenix Collaboration Oct 2015

Phi Meson Production In D Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole J. Apadula, Alan Dion, John C. Hill, Nels J. Hotvedt, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Timothy T. Rinn, Marzia Rosati, M. Shimomura, C. L. Silva, Arbin Timilsina, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX Collaboration has measured phi meson production in d + Au collisions at root s(NN) = 200 GeV using the dimuon and dielectron decay channels. The phi meson is measured in the forward (backward) d-going (Au-going) direction, 1.2 < y < 2.2 (-2.2 < y < -1.2) in the transverse-momentum (pT) range from 1-7 GeV/c and at midrapidity vertical bar y vertical bar < 0.35 in the p(T) range below 7 GeV/c. The phi meson invariant yields and nuclear-modification factors as a function of p(T), rapidity, and centrality are reported. An enhancement of phi meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p + p collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects.


Adsorption And Diffusion Of Ru Adatoms On Ru(0001)-Supported Graphene: Large-Scale First-Principles Calculations, Yong Han, James W. Evans Oct 2015

Adsorption And Diffusion Of Ru Adatoms On Ru(0001)-Supported Graphene: Large-Scale First-Principles Calculations, Yong Han, James W. Evans

Physics and Astronomy Publications

Large-scale first-principles density functional theory calculations are performed to investigate the adsorption and diffusion of Ru adatoms on monolayer graphene (G) supported on Ru(0001). The G sheet exhibits a periodic moiré-cell superstructure due to lattice mismatch. Within a moirécell, there are three distinct regions: fcc, hcp, and mound, in which the C6-ring center is above a fcc site, a hcp site, and a surface Ru atom of Ru(0001), respectively. The adsorption energy of a Ru adatom is evaluated at specific sites in these distinct regions. We find the strongest binding at an adsorption site above a C atom ...


Measurements Of Elliptic And Triangular Flow In High-Multiplicity He-3 + Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Alan Dion, Nathan C. Grau, John C. Hill, Nels J. Hotvedt, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Alexey Yu. Semenov, M. Shimomura, C. L. Silva, S. Skutnik, Arbin Timilsina, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Sep 2015

Measurements Of Elliptic And Triangular Flow In High-Multiplicity He-3 + Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Alan Dion, Nathan C. Grau, John C. Hill, Nels J. Hotvedt, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Alexey Yu. Semenov, M. Shimomura, C. L. Silva, S. Skutnik, Arbin Timilsina, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present the first measurement of elliptic (v(2)) and triangular (v(3)) flow in high-multiplicity He-3 + Au collisions at root s(NN) = 200 GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in He-3 + Au and in p + p collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the He-3 + Au system. The collective behavior is quantified in terms of elliptic v(2) and triangular v(3) anisotropy coefficients measured with respect to their corresponding event planes. The v(2) values are comparable to those ...


Systematic Study Of Azimuthal Anisotropy In Cu Plus Cu And Au Plus Au Collisions At Root S(Nn)=62.4 And 200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Sep 2015

Systematic Study Of Azimuthal Anisotropy In Cu Plus Cu And Au Plus Au Collisions At Root S(Nn)=62.4 And 200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We have studied the dependence of azimuthal anisotropy nu(2) for inclusive and identified charged hadrons in Au + Au and Cu + Cu collisions on collision energy, species, and centrality. The values of nu(2) as a function of transverse momentum pT and centrality in Au + Au collisions at root s(NN) = 200 and 62.4 GeV are the same within uncertainties. However, in Cu + Cu collisions we observe a decrease in nu(2) values as the collision energy is reduced from 200 to 62.4 GeV. The decrease is larger in the more peripheral collisions. By examining both Au + Au ...


Systematic Study Of Charged-Pion And Kaon Femtoscopy In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, John C. Hill, Nels J. Hotvedt, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Alexey Yu. Semenov, M. Shimomura, Arbin Timilsina, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Sep 2015

Systematic Study Of Charged-Pion And Kaon Femtoscopy In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, John C. Hill, Nels J. Hotvedt, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Timothy T. Rinn, Marzia Rosati, Alexey Yu. Semenov, M. Shimomura, Arbin Timilsina, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present a systematic study of charged-pion and kaon interferometry in Au + Au collisions at root s(NN) = 200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal-angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully ...


Oxygen Trapped By Rare Earth Tetrahedral Clusters In Nd4feos6: Crystal Structure, Electronic Structure, And Magnetic Properties, Qisheng Lin, Valentin Taufour, Yuemei Zhang, Max Wood, Thomas Drtina, Sergey L. Bud’Ko, Paul C. Canfield, Gordon J. Miller Sep 2015

Oxygen Trapped By Rare Earth Tetrahedral Clusters In Nd4feos6: Crystal Structure, Electronic Structure, And Magnetic Properties, Qisheng Lin, Valentin Taufour, Yuemei Zhang, Max Wood, Thomas Drtina, Sergey L. Bud’Ko, Paul C. Canfield, Gordon J. Miller

Chemistry Publications

Single crystals of Nd4FeOS6 were grown from an Fe–S eutectic solution. Single crystal X-ray diffraction analysis revealed a Nd4MnOSe6-type structure (P63mc, a=9.2693(1) Å, c=6.6650(1)Å, V=495.94(1) Å3, Z=2), featuring parallel chains of face-sharing [FeS6×1/2]4− trigonal antiprisms and interlinked [Nd4OS3]4+ cubane-like clusters. Oxygen atoms were found to be trapped by Nd4 clusters in the [Nd4OS3]4+ chains. Structural differences among Nd4MnOSe6-type Nd4FeOS6and the related La3CuSiS7− and Pr8CoGa3-type structures have been described. Magnetic susceptibility measurements on Nd4FeOS6 suggested the dominance of antiferromagnetic interactions at low ...


Origin Of Spin Gapless Semiconductor Behavior In Cofecrga: Theory And Experiment, Lakhan Bainsla, A. I. Mallick, M. Manivel Raja, A. A. Coelho, A. K. Nigam, Duane D. Johnson, Aftab Alam, K. G. Suresh Jul 2015

Origin Of Spin Gapless Semiconductor Behavior In Cofecrga: Theory And Experiment, Lakhan Bainsla, A. I. Mallick, M. Manivel Raja, A. A. Coelho, A. K. Nigam, Duane D. Johnson, Aftab Alam, K. G. Suresh

Ames Laboratory Publications

Despite a plethora of materials suggested for spintronic applications, a new class of materials has emerged, namely spin gapless semiconductors (SGS), which offers potentially more advantageous properties than existing ones. These magnetic semiconductors exhibit a finite band gap for one spin channel and a closed gap for the other. Here, supported by electronic-structure calculations, we report evidence of SGS behavior in equiatomic quaternary CoFeCrGa, having a cubic Heusler (prototype LiMgPdSn) structure but exhibiting chemical disorder (DO3 structure). CoFeCrGa is found to transform from SGS to half-metallic phase under pressure, which is attributed to unique electronic-structure features. The saturation magnetization (MS ...


Phase Transition In Bulk Single Crystals And Thin Films Of Vo2 By Nanoscale Infrared Spectroscopy And Imaging, Mengkun Liu, Aaron J. Sternbach, Martin Wagner, Tetiana V. Slusar, Sergey L. Bud'ko, Salinporn Kittiwatanakul, M. M. Qazilbash, Alexander Mcleod, Zhe Fei, Elsa Abreu, Jingdi Zhang, Michael Goldflam, Siyuan Dai, Guang-Xin Ni, Jiwei Lu, Hans A. Bechtel, Michael C. Martin, Markus B. Raschke, Richard D. Averitt, Stuart A. Wolf, Hyun-Tak Kim, Paul C. Canfield, D. N. Basov Jun 2015

Phase Transition In Bulk Single Crystals And Thin Films Of Vo2 By Nanoscale Infrared Spectroscopy And Imaging, Mengkun Liu, Aaron J. Sternbach, Martin Wagner, Tetiana V. Slusar, Sergey L. Bud'ko, Salinporn Kittiwatanakul, M. M. Qazilbash, Alexander Mcleod, Zhe Fei, Elsa Abreu, Jingdi Zhang, Michael Goldflam, Siyuan Dai, Guang-Xin Ni, Jiwei Lu, Hans A. Bechtel, Michael C. Martin, Markus B. Raschke, Richard D. Averitt, Stuart A. Wolf, Hyun-Tak Kim, Paul C. Canfield, D. N. Basov

Ames Laboratory Publications

We have systematically studied a variety of vanadium dioxide (VO2) crystalline forms, including bulk single crystals and oriented thin films, using infrared (IR) near-field spectroscopic imaging techniques. By measuring the IR spectroscopic responses of electrons and phonons in VO2 with sub-grain-size spatial resolution (∼20nm), we show that epitaxial strain in VO2 thin films not only triggers spontaneous local phase separations, but also leads to intermediate electronic and lattice states that are intrinsically different from those found in bulk. Generalized rules of strain- and symmetry-dependent mesoscopic phase inhomogeneity are also discussed. These results set the stage for a comprehensive understanding of ...


A Computational Study Of Diffusion In A Glass-Forming Metallic Liquid, T. Wang, F. Zhang, L. Yang, X. W. Fang, S. H. Zhou, Matthew J. Kramer, Cai-Zhuang Wang, Kai-Ming Ho, Ralph E. Napolitano Jun 2015

A Computational Study Of Diffusion In A Glass-Forming Metallic Liquid, T. Wang, F. Zhang, L. Yang, X. W. Fang, S. H. Zhou, Matthew J. Kramer, Cai-Zhuang Wang, Kai-Ming Ho, Ralph E. Napolitano

Materials Science and Engineering Publications

Liquid phase diffusion plays a critical role in phase transformations (e.g. glass transformation and devitrification) observed in marginal glass forming systems such as Al-Sm. Controlling transformation pathways in such cases requires a comprehensive description of diffusivity, including the associated composition and temperature dependencies. In the computational study reported here, we examine atomic diffusion in Al-Sm liquids using ab initio molecular dynamics (AIMD) and determine the diffusivities of Al and Sm for selected alloy compositions. Non-Arrhenius diffusion behavior is observed in the undercooled liquids with an enhanced local structural ordering. Through assessment of our AIMD result, we construct a general ...


Centrality Dependence Of Low-Momentum Direct-Photon Production In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration Jun 2015

Centrality Dependence Of Low-Momentum Direct-Photon Production In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au + Au collisions at root s(NN) = 200 GeV down to pT = 0.4 GeV/c. Photons are detected via photon conversions to e(+)e(-) pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low pT. We find an excess of direct photons above the N-coll-scaled yield measured in p + p collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/c in ...


Atomic Short-Range Order And Incipient Long-Range Order In High-Entropy Alloys, Prashant Signh, Andrei V. Smirnov, Duane D. Johnson Jun 2015

Atomic Short-Range Order And Incipient Long-Range Order In High-Entropy Alloys, Prashant Signh, Andrei V. Smirnov, Duane D. Johnson

Ames Laboratory Publications

Within density-functional theory, we apply an electronic-structure-based thermodynamic theory to calculate short-ranged order (SRO) in homogeneously disordered substitutional N-component alloys, and its electronic origin. Using the geometric properties of an (N−1) simplex that describes the Gibbs (compositional) space, we derive the analytic transform of the SRO eigenvectors that provides a unique description of high-temperature SRO in N-component alloys and the incipient low-temperature long-range order. We apply the electronic-based thermodynamic theory and the new general analysis to ternaries (A1 Cu-Ni-Zn and A2 Nb-Al-Ti) for validation, and then to quinary Al-Co-Cr-Fe-Ni high-entropy alloys for predictive assessment.


Specific Heat Investigation For Line Nodes In Heavily Overdoped Ba1−Xkxfe2as2, J. S. Kim, G. R. Stewart, Yong Liu, Thomas A. Lograsso Jun 2015

Specific Heat Investigation For Line Nodes In Heavily Overdoped Ba1−Xkxfe2as2, J. S. Kim, G. R. Stewart, Yong Liu, Thomas A. Lograsso

Ames Laboratory Publications

Previous research has found that the pairing symmetry in the iron-based superconductor Ba1−xKxFe2As2 changes from nodeless s wave near optimally doped, x≈0.4−0.55 and Tc>30K, to nodal (either d wave or s wave) at the pure end point, x=1 and Tc<4K. Intense theoretical interest has been focused on this possibility of changing pairing symmetry, where in the transition region both order parameters would be present and time-reversal symmetry would be broken. Here we report specific heat measurements in zero and applied magnetic fields down to 0.4 K of three individual single crystals, free of low-temperature magnetic anomalies, of heavily overdoped Ba1−xKxFe2As2,x=0.91, 0.88, and 0.81. The values for Tcmid are 5.6, 7.2, and 13 K and for Hc2≈4.5, 6, and 20 T, respectively. The data can be analyzed in a two-gap scenario, Δ2/Δ1≈4, with the magnetic field dependence of γ(=C/TasT→0) showing an anisotropic “S-shaped” behavior vs H, with the suppression of the lower gap by 1 T and γ≈H1/2 overall. Although such a nonlinear γ vs H is consistent with deep minima or nodes in the gap structure, it is not clear evidence for one, or both, of the gaps being nodal in these overdoped samples. Thus, following the established theoretical analysis of the specific heat of d-wave cuprate superconductors containing line nodes, we present the specific heat normalized by H1/2 plotted vs T/H1/2 of these heavily overdoped Ba1−xKxFe2As2 samples which—thanks to the absence of magnetic impurities in our sample—convincingly shows the expected scaling for line node behavior for the larger gap for all three compositions. There is, however, no clear observation of the nodal behavior C∝αT2 in zero field at low temperatures, with α≤2mJ/molK3 being consistent with the data. This, together with the scaling, leaves open the possibility of extreme anisotropy in a nodeless larger gap, Δ2, such that the scaling works for fields above 0.25–0.5 T (0.2–0.4 K in temperature units), where this is an estimate for the size of the deep minima in the Δ2∼20−25K gap. Therefore, the location of the change from nodeless to nodal gaps between optimally doped and heavily overdoped Ba1−xKxFe2As2 based on the present work may be closer to the KFe2As2 end point than x=0.91.


Refined Bcf-Type Boundary Conditions For Mesoscale Surface Step Dynamics, Renjie Zhao, David M. Ackerman, James W. Evans Jun 2015

Refined Bcf-Type Boundary Conditions For Mesoscale Surface Step Dynamics, Renjie Zhao, David M. Ackerman, James W. Evans

Physics and Astronomy Publications

Deposition on a vicinal surface with alternating rough and smooth steps is described by a solid-on-solid model with anisotropic interactions. Kinetic Monte Carlo (KMC) simulations of the model reveal step pairing in the absence of any additional step attachment barriers. We explore the description of this behavior within an analytic Burton-Cabrera-Frank (BCF)-type step dynamics treatment. Without attachment barriers, conventional kinetic coefficients for the rough and smooth steps are identical, as are the predicted step velocities for a vicinal surface with equal terrace widths. However, we determine refined kinetic coefficients from a two-dimensional discrete deposition-diffusion equation formalism which accounts for ...


Magnetic Interaction And Electronic Transport In La0.4bi0.6mn0.5ti0.5o3 Manganite, Vijaylakshmi Dayal, Punith Kumar V., Ravi L. Hadimani, E. A. Balfour, H. Fu, David C. Jiles May 2015

Magnetic Interaction And Electronic Transport In La0.4bi0.6mn0.5ti0.5o3 Manganite, Vijaylakshmi Dayal, Punith Kumar V., Ravi L. Hadimani, E. A. Balfour, H. Fu, David C. Jiles

Electrical and Computer Engineering Publications

We report magnetic interactions and electronic transport properties in La0.4Bi0.6Mn0.5Ti0.5O3 perovskite manganite synthesized using solid-state route. After characterizing the samples structurally, the systematic investigations of magnetic and electrical transport behaviors have been undertaken. It has been observed that at low temperatures near TC, the sample is magnetically frustrated leading to the second-order magnetic transition. A justification for the observed magnetic behavior has been explained based on Arrott's plot study. The resistivity as a function of temperature in the absence and the presence of applied magnetic field suggests semiconducting nature of the sample. The conduction of ...


Measurement Of Long-Range Angular Correlation And Quadrupole Anisotropy Of Pions And (Anti) Protons In Central D Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration May 2015

Measurement Of Long-Range Angular Correlation And Quadrupole Anisotropy Of Pions And (Anti) Protons In Central D Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central d + Au and minimum bias p + p collisions at root s(NN) = 200 GeV. The charged hadron is measured at midrapidity vertical bar eta vertical bar < 0.35, and the energy is measured at large rapidity (-3.7 < eta < -3.1, Au-going direction). An enhanced near-side angular correlation across vertical bar Delta eta vertical bar > 2.75 is observed in d + Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength v(2) for inclusive charged hadrons at midrapidity up to p(T) = 4.5 GeV/c. We also present the measurement of v(2) for identified pi(+/-) and (anti)protons in central d + Au ...


Coexistence Pressure For A Martensitic Transformation From Theory And Experiment: Revisiting The Bcc-Hcp Transition Of Iron Under Pressure, Nikolai A. Zarkevich, Duane D. Johnson May 2015

Coexistence Pressure For A Martensitic Transformation From Theory And Experiment: Revisiting The Bcc-Hcp Transition Of Iron Under Pressure, Nikolai A. Zarkevich, Duane D. Johnson

Ames Laboratory Publications

The coexistence pressure of two phases is a well-defined point at fixed temperature. In experiment, however, due to nonhydrostatic stresses and a stress-dependent potential energy barrier, different measurements yield different ranges of pressure with a hysteresis. Accounting for these effects, we propose an inequality for comparison of the theoretical value to a plurality of measured intervals. We revisit decades of pressure experiments on the bcc↔hcp transformations in iron, which are sensitive to nonhydrostatic conditions and sample size. From electronic-structure calculations, we find a bcc↔hcp coexistence pressure of 8.4GPa. We construct the equation of state for competing phases ...


Superconductivity Versus Structural Phase Transition In The Closely Related Bi2rh3.5s2 And Bi2rh3s2, Udhara S. Kaluarachchi, Weiwei Xie, Qisheng Lin, Valentin Taufour, Sergey L. Bud'ko, Gordon J. Miller, Paul C. Canfield May 2015

Superconductivity Versus Structural Phase Transition In The Closely Related Bi2rh3.5s2 And Bi2rh3s2, Udhara S. Kaluarachchi, Weiwei Xie, Qisheng Lin, Valentin Taufour, Sergey L. Bud'ko, Gordon J. Miller, Paul C. Canfield

Ames Laboratory Publications

Single crystals of Bi2Rh3S2 and Bi2Rh3.5S2 were synthesized by solution growth, and the crystal structures and thermodynamic and transport properties of both compounds were studied. In the case ofBi2Rh3S2, a structural first-order transition at around 165 K is identified by single-crystal diffraction experiments, with clear signatures visible in resistivity, magnetization, and specific heat data. No superconducting transition for Bi2Rh3S2 was observed down to 0.5 K. In contrast, no structural phase transition at high temperature was observed for Bi2Rh3.5S2; however, bulk superconductivity with a critical temperature, Tc≈1.7 K, was observed. The Sommerfeld coefficient γ and the ...


Heavy-Quark Production And Elliptic Flow In Au Plus Au Collisions At Root(Nn)-N-S=62.4 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration Apr 2015

Heavy-Quark Production And Elliptic Flow In Au Plus Au Collisions At Root(Nn)-N-S=62.4 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present measurements of electrons and positrons from the semileptonic decays of heavy-flavor hadrons at midrapidity (vertical bar gamma vertical bar < 0.35) in Au + Au collisions at root(NN)-N-S = 62.4 GeV. The data were collected in 2010 by the PHENIX experiment that included the new hadron-blind detector. The invariant yield of electrons from heavy-flavor decays is measured as a function of transverse momentum in the range 1 < p(T)(e) < 5 GeV/c. The invariant yield per binary collision is slightly enhanced above the p + p reference in Au + Au 0%-20%, 20%-40%, and 40%-60% centralities at a comparable level. At this low beam energy this may be a result of the interplay between initial-state Cronin effects, final-state flow, and energy loss in medium. The v(2) of electrons from heavy-flavor decays is nonzero when averaged between 1.3 < p(T)(e) < 2.5 GeV/c for 0%-40% centrality collisions at root(NN)-N-S = 62.4 GeV. For 20%-40% centrality collisions, the v(2) at root(NN)-N-S = 62.4 GeV is smaller than that for heavy-flavor decays at root(NN)-N-S = 200 GeV. The v2 of the electrons from heavy-flavor decay at the lower beam energy is also smaller than v(2) for pions. Both results indicate that the heavy quarks interact with the medium formed in these collisions, but they may not be at the same level of thermalization with the medium as observed at root(NN)-N-S = 200 GeV.


Kinetic Monte Carlo Simulation Of Statistical Mechanical Models And Coarse-Grained Mesoscale Descriptions Of Catalytic Reaction–Diffusion Processes: 1d Nanoporous And 2d Surface Systems, Da-Jiang Liu, Andrés Garcia, Jing Wang, David M. Ackerman, Chi-Jen Wang, James W. Evans Apr 2015

Kinetic Monte Carlo Simulation Of Statistical Mechanical Models And Coarse-Grained Mesoscale Descriptions Of Catalytic Reaction–Diffusion Processes: 1d Nanoporous And 2d Surface Systems, Da-Jiang Liu, Andrés Garcia, Jing Wang, David M. Ackerman, Chi-Jen Wang, James W. Evans

Physics and Astronomy Publications

Traditional mean-field rate equations of chemical kinetics for spatially uniform systems1−3 and the corresponding reaction−diffusion equations describing spatial heterogeneity4−6 have proved immensely useful in elucidating catalytic processes. However, it is well-recognized that standard mean-field rate expressions neglect spatial correlations in the reactant and/or product distribution. It is less well appreciated that the standard treatment of diffusion is generally applicable only at low concentrations and in unrestricted environments.


Discontinuous Non-Equilibrium Phase Transition In A Threshold Schloegl Model For Autocatalysis: Generic Two-Phase Coexistence And Metastability, Chi-Jen Wang, Da-Jiang Liu, James W. Evans Apr 2015

Discontinuous Non-Equilibrium Phase Transition In A Threshold Schloegl Model For Autocatalysis: Generic Two-Phase Coexistence And Metastability, Chi-Jen Wang, Da-Jiang Liu, James W. Evans

Physics and Astronomy Publications

Threshold versions of Schloegl's model on a lattice, which involve autocatalytic creation and spontaneous annihilation of particles, can provide a simple prototype for discontinuous non-equilibrium phase transitions. These models are equivalent to so-called threshold contact processes. A discontinuous transition between populated and vacuum states can occur selecting a threshold of N ≥ 2 for the minimum number, N, of neighboring particles enabling autocatalytic creation at an empty site. Fundamental open questions remain given the lack of a thermodynamic framework for analysis. For a square lattice with N = 2, we show that phase coexistence occurs not at a unique value but ...


Transitions Between Strongly Correlated And Random Steady-States For Catalytic Co-Oxidation On Surfaces At High-Pressure, Da-Jiang Liu, James W. Evans Apr 2015

Transitions Between Strongly Correlated And Random Steady-States For Catalytic Co-Oxidation On Surfaces At High-Pressure, Da-Jiang Liu, James W. Evans

Physics and Astronomy Publications

We explore simple lattice-gas reaction models for CO-oxidation on 1D and 2D periodic arrays of surface adsorption sites with CO adsorption and desorption, dissociative O2 adsorption and recombinative desorption (at low rate), and CO + O reaction to form CO2. Adspecies interactions are neglected, and adspecies diffusion is effectively absent. The models are motivated by studies of CO-oxidation on RuO2(110) at high-pressures. Despite the lack of adspecies interactions, negligible adspecies diffusion results in kinetically induced spatial correlations. A transition occurs from a random primarily CO-populated steady-state at high CO-partial pressure, pCO, to a strongly correlated near-O-covered steady-state for low pCO ...


Search For Dark Photons From Neutral Meson Decays In P Plus P And D Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Marzia Rosati, Alexey Yu. Semenov, M. Shimomura, C. L. Silva, Arbin Timilsina, Carla Vale, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration Mar 2015

Search For Dark Photons From Neutral Meson Decays In P Plus P And D Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Marzia Rosati, Alexey Yu. Semenov, M. Shimomura, C. L. Silva, Arbin Timilsina, Carla Vale, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g - 2)mu deviates from SM calculations by 3.6 sigma. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in pi(0), eta -> gamma e(+)e(-) decays and obtained upper limits of O(2 x 10(-6)) on U-gamma mixing at 90% C.L. for the mass ...


Platinum Nanoparticle During Electrochemical Hydrogen Evolution: Adsorbate Distribution, Active Reaction Species, And Size Effect, Teck L. Tan, Lin-Lin Wang, Jia Zhang, Duane D. Johnson, Kewu Bai Mar 2015

Platinum Nanoparticle During Electrochemical Hydrogen Evolution: Adsorbate Distribution, Active Reaction Species, And Size Effect, Teck L. Tan, Lin-Lin Wang, Jia Zhang, Duane D. Johnson, Kewu Bai

Ames Laboratory Publications

For small Pt nanoparticles (NPs), catalytic activity is, as observed, adversely affected by size in the 1–3 nm range. We elucidate, via first-principles-based thermodynamics, the operation H* distribution and cyclic voltammetry (CV) during the hydrogen evolution reaction (HER) across the electrochemical potential, including the underpotential region (U ≤ 0) that is difficult to assess in experiment. We consider multiple adsorption sites on a 1 nm Pt NP model and show that the characteristic CV peaks from different H* species correspond well to experiment. We next quantify the activity contribution from each H* species to explain the adverse effect of size ...


Measurement Of Gamma(1s+2s+3s) Production In P Plus P And Au Plus Au Collisions At Root Snn=200 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration Feb 2015

Measurement Of Gamma(1s+2s+3s) Production In P Plus P And Au Plus Au Collisions At Root Snn=200 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Measurements of bottomonium production in heavy-ion and p + p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three states, (1S + 2S + 3S), was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au + Au and p + p collisions at root sNN = 200 GeV. The (1S + 2S + 3S) -> e(+)e(-) differential cross section at midrapidity was found to be B(ee)d sigma/dy = 108 +/- 38 (stat) +/- 15 (syst) +/- 11 (luminosity) pb in p + p collisions. The nuclear modification factor in the 30% most central Au + Au collisions indicates a suppression ...


Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William Mccallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. Mcqueeney Feb 2015

Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William Mccallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. Mcqueeney

Ames Laboratory Publications

Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe0.953Co0.047)2As2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at TS, sets in well above the stripe antiferromagnetic ordering at TN. We find that the temperature-dependent dynamic susceptibility displays an anomaly at TS followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. Our findings can be consistently described by a model that ...


Charged-Pion Cross Sections And Double-Helicity Asymmetries In Polarized P Plus P Collisions At Root S=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration Feb 2015

Charged-Pion Cross Sections And Double-Helicity Asymmetries In Polarized P Plus P Collisions At Root S=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present midrapidity charged-pion invariant cross sections, the ratio of the pi(-) to pi(+) cross sections and the charge-separated double-spin asymmetries in polarized p + p collisions at root s = p + 200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The charge-separated pion asymmetries presented here sample ...