Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V12: Alloys and Compounds |
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Sponsoring Units: DCOMP Chair: Jifeng Sun, University of Missouri Room: 271 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V12.00001: Anisotropic resistivity in single crystals of the helical magnet ${\rm EuCo_{2}P_{2}}$ Makariy Tanatar, N.~S. Sangeetha, Abhishek Pandey, S.~L. Bud'ko, D.~C. Johnston, R. Prozorov The anisotropic resistivity is studied in single crystals of EuCo$_{2}$P$_{2}$, a model helical antiferromagnet with $T_{\rm N} \approx 66$~K [1]. Alignment of Eu$^{2+}$ magnetic moments $(S=7/2)$ parallel to the conducting planes leads to a monotonic decrease of the in-plane resistivity, $\rho_a (T)$, on cooling due to a decrease of the magnetic spin scattering. The inter-plane resistivity, $\rho _c (T)$, with current flowing along the helix axis ($c$-axis), reveals a resistivity increase starting above $T_{\rm N}$, echoing the onset of the entropy release determined by heat capacity measurements [1]. An additional anomaly occurs in $\rho_c(T)$ at $\sim 25$~K, which may reflect an incommensurate-to-commensurate transition in the helix wave vector on cooling, since the wave vector is known to be somewhat temperature dependent [2]. \newline [1] N.~S.~Sangeetha, E.~Cuervo-Reyes, A.~Pandey, and D.~C.~Johnston, Phys. Rev. B {\bf 94}, 014442 (2016). \newline [2] M.~Reehuis, W.~Jeitschko, M.~H.~M{\"o}ller, and P.~J.~Brown, J.~Phys.~Chem.~Solids {\bf 53}, 687 (1992). [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V12.00002: Dirac point and topologically nontrivial phase Minsung Kim, Cai-Zhuang Wang, Kai-Ming Ho It has been known that the topological phases of matters can be realized in both insulating and metallic band structures. Topological insulators have nontrivial band inversion between the valence and conduction bands, and topological Dirac semimetals have band crossings along high-symmetry paths in a Brillouin zone. In this work, we investigate a topological band structure where the valence band has nontrivial band topology and accidental band crossings occur giving rise to Dirac points that are protected by relevant point group symmetry. We discuss possible material realization of such topological phase using first-principles calculations based on density functional theory. We also examine the topological phase transitions between the bands constituting the Dirac points. [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V12.00003: Self-consistent full-potential relativistic KKR method Xianglin Liu, Yang Wang, Markus Eisenbach, G. Malcolm Stocks We implemented the self-consistent full potential relativistic KKR (Korringa-Kohn-Rostoker) method using the sine and cosine matrices formalism. In this scheme no irregular solution is needed, therefore it avoids the pathological behavior of the charge density at small radius. The poles of the single-site Green function are searched to identify the shallow bound states and resonance states, and to facilitate the energy integration of the Green function. As two examples, the bulk properties of noble metals are calculated, and the relativistic effects in polonium are investigated. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V12.00004: Combined semilocal exchange potential with dynamical mean-field theory Li Huang, Haiyan Lu The modern semilocal exchange potential is an accurate and efficient approximation to the exact exchange potential of density functional theory. We tried to combine it with the dynamical mean-field theory to derive a new first-principles many-body approach for studying correlated electronic materials. As a paradigm, this approach was employed to investigate the electronic structures and optical properties of strongly correlated ionic insulator YbS. Compared to the regular density functional theory plus dynamical mean-field theory which surprisingly failed to give an insulating solution, the new approach correctly captured all of the important characteristics of YbS. Not only an energy gap between a fully occupied Yb-4$f$ state and an unoccupied conduction band, but also an absence of Drude peak in the optical conductivity $\sigma(\omega)$ were successfully reproduced. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V12.00005: Entropy changes and caloric effects in RAl$_{\mathrm{2}}$ and RNi$_{\mathrm{5}}$ single crystals Nilson Antunes de Oliveira In this work we theoretically discuss the entropy changes and the caloric properties of RAl$_{\mathrm{2}}$, RNi$_{\mathrm{5}}$ single crystals where R stands for rare earth element. For this purpose, we use a model of interacting magnetic moments including an extra term to take into account the magnetocrystalline anisotropy [1]. We perform calculations for different physical scenarios and make a comparative study of the conventional and rotating magnetocaloric effects in these compounds. Our calculations show that in RAl$_{\mathrm{2}}$ the conventional magnetocaloric quantities are large. Besides that, our calculations also show that RAl$_{\mathrm{2}}$ compounds may exhibit change of sign in the caloric quantities, for some values of the magnetic field applied in a given direction. However, the corresponding rotating magnetocaloric quantities are not so large. In the case of RNi$_{\mathrm{5}}$ our calculations predict large values for both the conventional and rotating magnetocaloric quantities. Part of our results is in good agreement with the available experimental data[2] and some of them need experimental data to be confirmed. [1] N. A. de Oliveira and P. J. von Ranke, Phys. Rep. \textbf{489}, 89 (2010). [2] M. Patra et al, Jour. Phys.:Cond Mat. \textbf{26}, 046004 (2014). [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V12.00006: Predictive analysis of the influence of the chemical composition and pre-processing regimen on structural properties of steel alloys using machine learning techniques. Narayanan Krishnamurthy, Siddharth Maddali, Vyacheslav Romanov, Jeffrey Hawk We present some structural properties of multi-component steel alloys as predicted by a random forest machine-learning model. These non-parametric models are trained on high-dimensional data sets defined by features such as chemical composition, pre-processing temperatures and environmental influences, the latter of which are based upon standardized testing procedures for tensile, creep and rupture properties as defined by the American Society of Testing and Materials (ASTM). We quantify the goodness of fit of these models as well as the inferred relative importance of each of these features, all with a conveniently defined metric and scale. The models are tested with synthetic data points, generated subject to the appropriate mathematical constraints for the various features. By this we highlight possible trends in the increase or degradation of the structural properties with perturbations in the features of importance. This work is presented as part of the Data Science Initiative at the National Energy Technology Laboratory, directed specifically towards the computational design of steel alloys. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V12.00007: Linking Microstructural Evolution and Tribology in Metallic Contacts Michael Chandross, Shengfeng Cheng, Nicolas Argibay Tribologists rely on phenomenological models to describe the seemingly disjointed steady-state regimes of metal wear. Pure metals such as gold -- frequently used in electrical contacts -- exhibit high friction and wear. In contrast, nanocrystalline metals often show much lower friction and wear. The engineering community has generally used a phenomenological connection between hardness and friction/wear to explain this macroscale response and guide designs. We present results of recent simulations and experiments that demonstrate a general framework for connecting materials properties (i.e. microstructural evolution) to tribological response. We present evidence that competition between grain refinement (from cold working), grain coarsening (from stress-induced grain growth), and wear (delamination and plowing) can be used to describe transient and steady state tribological behavior of metals, alloys and composites. We explore the seemingly disjointed steady-state friction regimes of metals and alloys, with a goal of elucidating the structure-property relationships, allowing for the engineering of tribological materials and contacts based on the kinetics of grain boundary motion. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V12.00008: Density-Functional Theory description of transport in the single-electron transistor Krissia Zawadzki, Luiz N. Oliveira The Kondo effect governs the low-temperature transport properties of the single electron transistor (SET), a quantum dot bridging two electron gases. In the weak coupling limit, for odd dot occupation, the gate-potential profile of the conductance approaches a step, known as the Kondo plateau. The plateau and other SET properties being well understood on the basis of the Anderson model, more realistic (i.~e., DFT) descriptions of the device are now desired. This poses a challenge, since the SET is strongly correlated. DFT computations that reproduce the conductance plateau have been reported, e.~g., by Bergfield et al., Phys.\ Rev.\ Lett.~\textbf{108}, 066801 (2012), which rely on the exact functional provided by the Bethe-Ansatz solution for the Anderson model. Here, sticking to DFT tradition, we employ a functional derived from a homogeneous system: the parametrization of the Lieb-Wu solution for the Hubbard model due to Fran\c ca et al., New\ J.\ Phys.~\textbf{14}, 073021 (2012). Our computations reproduce the plateau and yield other results in accurate agreement with the exact diagonalization of the Anderson Hamiltonian. The prospects for extensions to realistic descriptions of two-dimensional nanostructured devices will be discussed. [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V12.00009: Progress towards an effective model for FeSe from high-accuracy first-principles quantum Monte Carlo Brian Busemeyer, Lucas K. Wagner While the origin of superconductivity in the iron-based materials is still controversial, the proximity of the superconductivity to magnetic order is suggestive that magnetism may be important. Our previous work has suggested that first-principles Diffusion Monte Carlo (FN-DMC) can capture magnetic properties of iron-based superconductors that density functional theory (DFT) misses, but which are consistent with experiment. We report on the progress of efforts to find simple effective models consistent with the FN-DMC description of the low-lying Hilbert space of the iron-based superconductor, FeSe. We utilize a procedure outlined by Changlani et al.[1], which both produces parameter values and indications of whether the model is a good description of the first-principles Hamiltonian. Using this procedure, we evaluate several models of the magnetic part of the Hilbert space found in the literature, as well as the Hubbard model, and a spin-fermion model. We discuss which interaction parameters are important for this material, and how the material-specific properties give rise to these interactions. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V12.00010: Finding Effective Models in Transition Metals using Quantum Monte Carlo Kiel Williams, Lucas K. Wagner There is a gap between high-accuracy ab-initio calculations, like those produced from Quantum Monte Carlo (QMC), and effective lattice models such as the Hubbard model. We have developed a method that combines data produced from QMC with fitting techniques taken from data science, allowing us to determine which degrees of freedom are required to connect ab-initio and model calculations[1]. We test this approach for transition metal atoms, where spectroscopic reference data exists. We report on the accuracy of several derived effective models that include different degrees of freedom, and comment on the quality of the parameter values we obtain from our fitting procedure. [1] Changlani, Zheng, and Wagner J. Chem. Phys. 143, 102814 (2015). [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V12.00011: Calculating electronic correlation effects from densities of transitions Roger Haydock Adding a localized electron to a system of interacting electrons induces a density of transitions described by the time-independent Heisenberg equation. Sequences of these transitions generate interacting states whose total energy is the sum of energies of the constituent transitions. A calculation of magnetic moments for itinerant electrons with Ising interactions illustrates this method. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V12.00012: The applications of silver think films for the transparent conducting films applications. Jui-Hung Hsu Two important issues for the transparent conducting films (TCFs) are optical transparency and electrical conductivity, which are self-contradiction. Metallic thin films are the first materials used as the TCFs, but now are replaced by the transparent conducting oxides with plasma oscillator frequency below the visible frequency. The fact that metals have high extinction coefficients indicates that metals should be not transparent until an extremely low thickness. Hence a general belief is that the transparency for the metal thin films is not good enough for the TCF applications. One example is silver, which has a complex refractive index of n $=$ 0.044 $+$ 3.61i at 550 nm, and results in a high bulk reflectivity (R $=$ 0.987) and small penetration depth (12 nm). However, recently publications incorporate metal thin films into TCF structures demonstrate that the structures have high transparency as well high conductivity, which seems to contradict to the belief mentioned above. Here we present our results that the transparency for the silver metallic thin films can be much higher than expected. Considering the high electrical conductivity of the silver, a thin film incorporating silver thin films can have better performance among the TCFs. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V12.00013: Controlling material reactivity using architecture Kyle Sullivan, Cheng Zhu, Eric Duoss, Matt Durban, Alex Gash, Alexandra Golobic, Michael Grapes, Joshua Kuntz, Christopher Spadaccini, David Kolesky, Jennifer Lewis Thermites are mixtures of a metal fuel with a metal oxide as the oxidizer. The reactivity of such materials can be tailored through careful selection of a variety of parameters, and can range from very slow burns to rapid deflagrations when using nanoparticles. However, in some cases diminishing returns have been observed as the particle size is reduced. 3D printing is a rapidly emerging field, which offers the capability of printing architected parts; for example parts with controlled internal feature sizes and geometries. In this work, we investigated whether such features could be utilized to gain additional control of the reactivity. This talk introduces several new methods for preparing thermite samples with controlled architectures using direct 3D printing, deposition, and/or casting. Additionally, we demonstrate that 3D printing can be used to tailor the convective and/or advective energy transport during a deflagration, thus enhancing or retarding the reaction. The results are promising in that they give researchers additional ways to control the energy release rate, without defaulting to the classic approach of changing the formulation. This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-708525. [Preview Abstract] |
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