Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session M33: Metal Physics: Thermodynamics ,Transport ,Optical Properties, Electronic Structure, etc. |
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Sponsoring Units: DCMP Chair: Markus Eisenbach, Oak Ridge National Laboratory Room: 208 |
Wednesday, March 4, 2015 11:15AM - 11:27AM |
M33.00001: Chemical Physics and Properties of ThPt$_2$ Andreas Leithe-Jasper, Roman Gumeniuk, Walter Schnelle, Michael Nicklas, Yuri Grin ThPt$_2$ crystallizes with a unique type of structure (space group $I4/mmm$, $a = 4.1569(2)$\,\AA, $c = 14.3678(6)$\,\AA, which belongs to the group of the close-packed tetragonal structures (Pearson symbol $tI12$). An analysis of the chemical bonding by the electron density/electron localizability approach reveals formation of two-dimensional platinum anions separated by the Th cations. Measurements of magnetic susceptibility, electrical resistivity and specific heat show ThPt$_2$ to be diamagnetic with good metallic conductivity ($rho(300\,K) \approx 8.5 \mu\Omega$\,cm). The properties are in good agreement with the calculated electronic structure with a low DOS ($N(E_F) = 0.92$ states eV$^{-1}$ f.u$^{-1}$). The stability of the compound with respect to other possible structural modifications was studied theoretically. [Preview Abstract] |
Wednesday, March 4, 2015 11:27AM - 11:39AM |
M33.00002: Entropy changes and caloric effects in $RAl_{2}$ single crystals Nilson Antunes de Oliveira, Julieth Caro Pati\~no, Pedro J. von Ranke In this work we theoretically discuss the entropy changes and the caloric effects in RAl2 single crystals, which crystalize in the cubic symmetry and have large magneto crystalline anisotropy due to the crystal electric field. For this purpose, we use a model of interacting magnetic moments including a term to account for the crystal electric field. We apply the model to calculate the entropy changes and the magnetocaloric quantities in TmAl2 and NdAl2 by applying magnetic field variations in different crystallographic directions. Our calculations for the entropy changes in these compounds are in a reasonable agreement with the available experimental data for $\Delta B=7$ $T$. Further experimental data are necessary to compare with our theoretical predictions for the adiabatic temperature change. We also calculate the caloric quantities by fixing the magnitude of the magnetic field and rotating its direction. In this case, our calculations predict an anomaly (i.e. a change of sign) in the caloric quantities of TmAl2 when a magnetic field of 3 T rotates from $<100>$ to $<110>$ direction. A similar behavior is also observed in NdAl2. This very interesting fact, which is basically due to the magneto crystalline anisotropy, needs experimental data to be confirmed [Preview Abstract] |
Wednesday, March 4, 2015 11:39AM - 11:51AM |
M33.00003: First-principles molecular dynamics simulations of high-concentration deuterium implantation in liquid lithium Mohan Chen, Tyler Abrams, Michael Jaworski, Emily Carter First-principles molecular dynamics (FPMD) is performed to study liquid lithium (Li) samples with high-concentration deuterium (D) implantation. First, we validate FPMD against experimental properties of solid and liquid Li and LiD. The calculated properties of both Li and LiD include relative stabilities and bulk moduli of several solid phases, melting temperatures, pair distribution functions, and bond angle distribution functions. Excellent agreement is obtained between FPMD and available experimental data. Next, we randomly implant D atoms at four different concentrations into liquid Li at different temperatures. Specifically, the ratios of D:Li atoms studied are 0.25, 0.50, 0.75 and 1.00, and the temperatures range from 400 to 1143 K. FPMD reveals several interesting properties of these liquid Li samples with implanted D atoms. For example, we observe fast nucleation of rock-salt structures of LiD for samples at temperatures lower than the melting point of LiD (960 K). We find that the pure Li component is quickly suppressed with increased concentration of D atoms, and that no D clusters form. Finally, because measured diffusivities of D in liquid Li vary by several orders of magnitude, we predict the diffusivities of both Li and D atoms in all samples. [Preview Abstract] |
Wednesday, March 4, 2015 11:51AM - 12:03PM |
M33.00004: Spin-phonon interactions to control the thermal transport in uranium dioxide K. Gofryk, S. Du, C.R. Stanek, J.C. Lashley, X.-Y. Liu, R.K. Schulze, J.L. Smith, D.J. Safarik, D.D. Byler, K.J. McClellan, B.P Uberuaga, B.L. Scott, D.A. Andersson Despite more than sixty years of intense research of uranium dioxide, a thorough understanding is lacking for the microscopic processes that control its transport and thermodynamic properties. In particular, it is not clear how different degrees of freedom and quasiparticle excitations interact and what is the relationship to the thermal behavior. We report our new experimental and theoretical studies on oriented and well characterized single crystals of uranium dioxide. Our results indicate that strong spin-phonon coupling and resonant scattering are important for understanding the general thermal behavior, and also explains the observed anisotropy in thermal conductivity by coupling to the applied temperature gradient and breaking cubic symmetry. We will discuss implications of these results. [Preview Abstract] |
Wednesday, March 4, 2015 12:03PM - 12:15PM |
M33.00005: Simulating Order Parameters for Phase Transitions in Alloys Richard R. Vanfleet, Conrad W. Rosenbrock, Gus L.W. Hart, Branton J. Campbell When determining the structure of alloys using diffraction patterns, possible distortions that lower the symmetry of the parent phase can be limited by group-theoretical arguments as long as a group-subgroup relationship exists between the parent and distorted phases$^1$. Order parameters are vectors in representation space where each dimension corresponds to a specific superlattice vector in reciprocal space (e.g. L = [0.5,0.5,0.5] or X=[1,0,0]); such order parameters determine the distortions that may arise during a phase transition. By measuring the Fourier transform of the structure at each relevant superlattice vector during a Monte Carlo simulation for CuPt$_3$, we were able to extract these thermodynamic order parameters and qualitatively confirm distortions in the L and X order parameters observed in experiment$^2$. The methodology presents a highly effective avenue for comparing simulated phase transitions with experimental results. \\ \\ \mbox{[1]} Harold T. Stokes, Branton J. Campbell and Dorian M. Hatch. \textit{Order parameters for phase transitions to structures with one-dimensional incommensurate modulations} \\ \mbox{[2]} Rokuro Miida and Denjiro Watanabe. \textit{Electron Microscope and Diffraction Study on the Ordered Structures of Platinum-Rich Cu-Pt Alloys} [Preview Abstract] |
Wednesday, March 4, 2015 12:15PM - 12:27PM |
M33.00006: Concentration Waves in High-Entropy Alloys - a new alloy design approach Prashant Singh, Duane D. Johnson Chemical short-range order (SRO) in solid solutions can be interpreted as a ``concentration wave'' - a Fourier decomposition of nascent order - identified experimentally via Warren-Cowley SRO parameters. We present a rigorous thermodynamic theory to predict and uniquely interpret the SRO in N$-$component alloys. Based on KKR-CPA electronic structure, we implemented this method using thermodynamic linear-response to include all alloying effects, e.g., band-filling, hybridization, Fermi$-$surface nesting and van Hove instabilities. We apply this first-principles method to high-entropy alloys (HEAs), i.e., solid solutions with N$>$4 that inhibit small-cell order due to large entropy competing against ordering enthalpy, as their properties are sensitive to SRO. We validated theory with comparison to experiments in A2 Nb-Al-Ti and A1 Cu-Ni-Zn . We then predict and analyze SRO and mechanical trends in Ni-Ti-Zr-Cu-Al and Co-Cr-Fe-Mn-Ni systems - showcasing this new first-principles-based alloy design method. [Preview Abstract] |
Wednesday, March 4, 2015 12:27PM - 12:39PM |
M33.00007: Magnetic Landau free energy density for the bcc-hcp phase transformation Mahdi Sanati, Robert C. Albers, Turab Lookman, Avadh Saxena We have studied the he bcc-hcp phase transformation in Fe and Co with the use of first-principles calculations. The complete energy surface as the system goes from the bcc to hcp structure is determined. The results are used to find an appropriate Landau free energy (LFE) density for describing this transformation. The Landau free energy consists of three order parameters: shear, shuffle, and magnetization. The coefficients of the Landau free energy density are obtained from first-principles energy fits. The stability of the bcc phase in both elements has been studied and the results are then extended to understand the stability of the bcc Fe-Co alloys with varying stoichiometry. [Preview Abstract] |
Wednesday, March 4, 2015 12:39PM - 12:51PM |
M33.00008: Vibrational entropy changes the solid solubility of a random alloy at high temperatures Nina Shulumba, Olle Hellman, Zamaan Raza, Jenifer Barrirero, Frank M\"{u}cklich, Igor A. Abrikosov, Magnus Od\'{e}n We have developed a method to accurately and efficiently determine vibrational entropy as a function of temperature and volume for substitutional alloys from first principles. Using Ti$_{1-x}$Al$_x$N metal alloy as a model system we calculate the isostructural phase diagram by minimization of the free energy, solving the original Gibbs problem of finding its global minimum corresponding to the true equilibrium state of the system. We demonstrate that the vibrational contribution to the free energy has a decisive impact on the calculated phase diagram of Ti$_{1-x}$Al$_x$N alloy, lowering the maximum temperature for the miscibility gap from 9000 K to 2400 K. The solubility limit of the predicted phase diagram is experimentally verified by local chemical composition measurements of thermally aged Ti$_{50}$Al$_{50}$N alloys. [Preview Abstract] |
Wednesday, March 4, 2015 12:51PM - 1:03PM |
M33.00009: Chiral magnetic effect and SdH oscillations in Dirac and Weyl metals Dmitri Kharzeev, Gustavo Monteiro, Alexander Abanov In the present work, we consider the interplay of chiral anomaly and Shubnikov-de Haas (SdH) oscillations in recently discovered Dirac metals. The kinetic theory describing the transport in these new materials should account for the chiral anomaly. The unbalanced number of chiral zero-modes in the presence of magnetic field due to the chiral anomaly gives rise to an additional contribution to the electric current -- the chiral magnetic effect [1]. The zero-modes are topologically protected from scattering and their contribution to the current leads to a negative magnetoresistance [2]. This effect was recently observed in measurements on the Dirac semimetal $Cd_3As_2$ [3], where the longitudinal (with respect to magnetic field) component of the resistivity tensor shows a negative slope, along with pronounced Shubnikov-de Haas (SdH) oscillations. We develop a combined description of both these phenomena within a chiral kinetic theory. \newline [1] K. Fukushima, D. E. Kharzeev, and H. J. Warringa, Phys. Rev. D \textbf{78}, (2008). \newline [2] D. T. Son and B. Spivak, Phys Rev B \textbf{88}, (2013). \newline [3] T. Liang, Q. Gibson, M. N. Ali, M. Liu, R. J. Cava, and N. P. Ong, arXiv:1404.7794 [cond-mat.str-el] (2014). [Preview Abstract] |
Wednesday, March 4, 2015 1:03PM - 1:15PM |
M33.00010: Excited-state electron-dynamics probed by A1g phonons in Bi, Sb, and Bi2Te3 Crystal Bray, Eamonn Murray, Stephen Fahy, David Reis We report on dynamics of photo-excited electronic states in bismuth, antimony and bismuth telluride as a function of photon energy and carrier density using the coherent A1g phonon as a probe. Previous experimental and first principle theoretical studies on group V semimetals show strong softening of the mode with photo-excitation associated with electronic softening and a reduction in the Peierls distortion. By carefully controlling the total energy deposition and the incident photon number as a function of different pump wavelengths, we are able to further the experimental results producing constraints on relaxation and population mechanism to model an exited system to help reconcile differences between the one- and two-chemical potential theories that use various Fermi Dirac distributions to describe thermalization of electron and hole populations. [Preview Abstract] |
Wednesday, March 4, 2015 1:15PM - 1:27PM |
M33.00011: Hydrodynamics of Dirac and Weyl materials Gustavo Monteiro, Alexander Abanov, V. Parameswaran Nair The study of transport in Weyl and Dirac metals should account for additional contributions to the electric current coming from the chiral anomaly, namely chiral magnetic and chiral vortical effects. These responses are non-dissipative and fully characterized by the chiral anomaly coefficient. In addition, they are believed to be robust even in a strongly interacting regime, due to the topological nature of the anomaly. The fundamental equations for the hydrodynamic limit of such transports were introduced in [1], in order to describe the quark-gluon plasma in nuclear collision. Having these equations as starting point, we present a variational principle for them and discuss the canonical structure of the corresponding hydrodynamic modes [2]. \newline [1] D. T. Son and P. Surowka, Phys. Rev. Lett. 103, (2009). \newline [2] G. Monteiro, A. G. Abanov and V. P. Nair, arXiv:1410.4833 [hep-th] (2014). [Preview Abstract] |
Wednesday, March 4, 2015 1:27PM - 1:39PM |
M33.00012: Electronic properties and electron-phonon interaction in complex, multicomponent alloys in application to high-entropy alloys German Samolyuk, Markus Daene, George Malcolm Stocks, Jose Alfredo Caro, Roger Stoller High-entropy alloys (HEAs) have recently been developed as nontraditional alloy systems. They are composed of multiple elements at or near equiatomic ratios that form random solid solutions on simple underlying fcc or bcc lattices. In recent years HEAs have attracted significant attention due to their high strength, ductility and possible high radiation resistance. The complexity of the alloys results in very interesting electronic system behavior. Even in thermal equilibrium, disorder, especially extreme disorder, has important impacts on all electronic, atomic, and magnetic properties. In the current work we present results of first principle investigation of the electronic and magnetic properties of Ni-based multicomponent concentrated alloys using the coherent potential approximation (CPA). The influence of electronic structure modifications on the electron mean free path and values of electron-phonon coupling are calculated, together with preliminary results on similar quantities obtained by Time Dependent DFT. We discuss possible effects of tuning the mean free path and energy dissipation mechanisms to defect production and recombination in HEAs under irradiation. [Preview Abstract] |
Wednesday, March 4, 2015 1:39PM - 1:51PM |
M33.00013: Effect of dopants in Cu single grain boundaries Mathieu Cesar, Daniel Gall, Hong Guo The downscaling of integrated circuits is presently limited by the so called size effect in Cu interconnects. One of the two major contributions to this increased resistivity is known to be grain boundary (GB) electron scattering [1]. We demonstrated that Cu single GB resistance can be calculated accurately from first principles using a combination of plane wave density functional theory for structural relaxation and non-equilibrium Green's function for transport [2]. We now determine the effect of the presence of dopants in the GBs using the novel non-equilibrium coherent potential approximation [3] and discuss the possibility of reduced resistance in doped Cu GBs. [1]: T.S. Kuan, C.K. Inoki, G.S. Oehrlein, K. Rose, Y.P. Zhao, G.C. Wang, S.M. Rossnagel, and C. Cabral, MRS Proc. 612, D7.1.1 (2000). [2]: M. Cesar, D. Liu, D. Gall, and H. Guo, Phys. Rev. Appl. 2 (4), 044007 (2014). [3]: Y. Zhu, L. Liu, and H. Guo, Phys. Rev. B 88 (20), 205415 (2013). [Preview Abstract] |
Wednesday, March 4, 2015 1:51PM - 2:03PM |
M33.00014: Microscopic derivation of Ginzburg-Landau theory of weak crystallization Ivar Martin, Sarang Gopalakrishnan, Eugene Demler Theory of weak crystallization has been applied in the past to understand the relative stability of various crystalline phases. It contains however a number of phenomenological constants and functions, about which typically only generic assumptions are made. We demonstrate how to derive the theory of weak crystallization of metals and metallic alloys starting from the basic mixture of electrons and ions. We find a non-trivial structure of GL parameters, which helps to shed light, in particular, on the stability of quasicrystals. [Preview Abstract] |
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