Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X31: Metals and Metal Physics II |
Hide Abstracts |
Sponsoring Units: DMP Chair: Jifeng Sun, Univ of Missouri - Columbia Room: LACC 407 |
Friday, March 9, 2018 8:00AM - 8:12AM |
X31.00001: Coexistence of topological bosons and topological fermions in triple-point-metals Sobhit Singh, QuanSheng Wu, Alexey Soluyanov, Aldo Romero Recent progress in the discovery of Dirac and Weyl fermions in crystal systems has inspired researchers to search for other novel fermionic quasi-particles that are topologically protected by the crystal symmetries, and are beyond the Dirac, Weyl and Majorana classification scheme. Recently, three-component fermions which show fermionic statistics with an integer (pseudo)spin degree of freedom have been discovered in the triple-point-metals (TPM) [1,2]. Akin to the topological fermionic systems, researchers have also theoretically envisioned and experimetnally detected topological bosonic quasiparticles in photonic and phononic crystals at kHz frequency [3,4]. Here we demonstrate the appearance a new three-component topological bosonic excitation at THz frequency near a triply-degenerate gapless point in the phonon spectra of special TPM. Interestingly, this three-component boson coexists with the three-component fermions, and both appear near the same point in the reciprocal space. Both type-I and type-II Weyl fermions have also been spotted the studied material. |
Friday, March 9, 2018 8:12AM - 8:24AM |
X31.00002: Topological Nodal Lines from Crystalline Symmetry Heqiu Li, Chen Fang, Kai Sun Topological nodal lines protected by the time-reversal and space-inversion symmetry can be classified into two categories, depending on the value of the $Z_2$ monopole topological index. Nodal lines with trivial (non-trivial) monopole charge can (cannot) be gapped out via shrinking the nodal line into a point. In this study, we provide a general principle for finding topological nodal lines with nontrivial monopole charge based on the interplay between lattice crystalline symmetries and the time-reversal symmetry. In addition, this study also reveals a new family of topological nodal lines, protected by the time-reversal symmetry and point group symmetries. |
Friday, March 9, 2018 8:24AM - 8:36AM |
X31.00003: 3D Dirac cone signature in the optical conductivity of BaNiS2 David Santos-Cottin, Michele Casula, Luca De Medici, Yannick Klein, Andrea Gauzzi, Ricardo Lobo BaCo1-xNixS2 is a quasi-2D Mott system, where electron doping drives the antiferromagnetic and insulating phase at x=0 to a metallic and paramagnetic one at the critical value xcr = 0.22 [1]. ARPES measurements on high-quality single crystals of BaNiS2 and band structure calculations suggest a moderate renormalization effect due to weak electronic correlations and a large Rashba coupling amplified by a huge staggered crystal field [2]. ARPES and Quantum Oscillation measurements allowed to propose the first experimental Fermi surface in which a 3D Dirac cone, presumably symmetry protected, emerged in middle of GM direction [3]. |
Friday, March 9, 2018 8:36AM - 8:48AM |
X31.00004: Machine Learning to Analyze the Atomic Energy Landscape in Poly-Crystalline Materials Tristan Sharp, Spencer Thomas, Ekin Cubuk, Samuel Schoenholz, David Srolovitz, Andrea Liu Plastic deformation of poly-crystalline materials occurs at defects such as grain boundaries. At a small scale, the plasticity typically consists of atoms at the defect core shifting between metastable positions (rearranging). Predicting these rearrangements at grain boundaries is challenging due to the structural complexity. We adapt a machine learning technique used successfully on disordered glassy materials to study atomic plasticity in crystalline metals. We first catalog the atomic rearrangements that occur, in large MD simulations of poly-crystalline aluminum and nickel at finite temperature. We train a support vector machine (SVM) to identify the local structure surrounding a particle just before it rearranges. The SVM classifies structures as susceptible to rearrangement with 90% accuracy in cross-validation. For each atom, we calculate a value derived from the SVM that is correlated with the susceptibility to rearrange, called softness, which provides a new view on atomic-scale plasticity in poly-crystals. We obtain a well-defined energy barrier for rearrangements for grain boundary particles and find that the average energy barrier is consistent with published experimental measurements. |
Friday, March 9, 2018 8:48AM - 9:00AM |
X31.00005: First-principles Calculation of Atomic Location of 3d Transition Metal Elements in B2-type Ti-Ni Alloy Sukeyoshi Yamamoto, Tomohito Yokomine, Hiroyuki Morishita, Kazunori Sato, Tomoyuki Terai, Takashi Fukuda, Tomoyuki Kakeshita Ti-Ni alloy is one of the widely-used shape memory alloys and its martensitic transformation can be controlled by introducing 3d transition metal (3d-TM) elements. To clarify the effects of 3d-TM elements, Nakata et al., investigated atomic location of 3d-TM by using the ALCHEMI technique [1], and found that Fe and Co (Sc) favor Ni (Ti) site. The location of V, Cr, Mn and Cu depends on the Ti-Ni ratio. In this paper, we perform first-principles calculations on these alloy systems, and discuss electronic origin of the location of 3d-TM in B2-type Ti-Ni. For the present calculations, we use VASP code [2] and calculate formation energy of substitutional 3d-TM in B2-type TiNi. It is found that Cr, Mn, Fe and Co favor Ni site, and Sc favors Ti site. V and Cu can replace both sites. We also perform COHP analysis [3] and it is found that the chemical trend of the atomic location can be understood from the viewpoint of chemical bonding between 3d-TM and neighboring Ti and Ni. |
Friday, March 9, 2018 9:00AM - 9:12AM |
X31.00006: Global minimum and new metastable atomic structures of metal clusters Nabil Alaqtash, Renat Sabirianov The evolutionary algorithm coupled with density functional (DFT) method is used to identify the global energy minimum and the metastable atomic structures of metal clusters, as implemented in USPEX, we studied the atomic structure, binding energies, effective coordination numbers, average bond lengths, and magnetic properties of 13-atom Cu, Co and Cr clusters. A set of metastable and global minimum atomic structures as supported by vibrational analysis are identified. Global energy metastable configurations are identified for 13- atom Cu, Co and Cr clusters and previous known global minimum atomic structures were confirmed by our calculations. We found that the Cu13 cluster has a distorted hexagonal bilayer (HBL)-like structure, which is composed by two layers as in the ideal HBL structure. The distorted HBL Cu13 is 1.09 eV lower in total energy compared to close-packed icosahedral (ICO) configuration. Our calculations show that Co13 has an ideal HBL structure and Cr13 cluster has distorted ICO structure. Moreover, our calculations show that Cr13 has another lower energy atomic configuration with 0.13 eV difference form ICO. Cr13 has ferrimagnetic (FIM) interaction which plays an important role in finding the lowest energy structure. |
Friday, March 9, 2018 9:12AM - 9:24AM |
X31.00007: Laser Induced Two Way Shape Memory Effect in NiTi Alloy Saidjafarzoda Ilhom, Trason Carter, Khomidkhodzha Kholikov, Peizhen Li, Dovletgeldi Seyitliyev, Zachary Thomas, Haluk Karaca, Omer San, Ali Er Shape memory alloys (SMAs) are a unique class of smart materials widely used in biomedical and aerospace technologies. Here, we report an efficient and low-cost direct imprinting method to create thermally controllable surface patterns. Patterned micro-indents were generated on Ni50Ti50 (at. %) using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. The effects of laser energy, shape recovery of NiTi, and simulation of shock wave was studied. Laser pulses were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Optical microscope images showed that surface patterns with tailorable sizes can be obtained. The depth of the patterns increases with laser power and irradiation time. Upon heating, the depth profile of SMA surfaces changed where the maximum depth recovery ratio of 30 % was observed. The recovery ratio decreased and leveled off at about 15 % when the number of pulses and thus the well depth was increased. A numerical simulation of pressure evolution in SMAs showed a good agreement with the experimental results. The stress wave closely followed the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were observed. |
Friday, March 9, 2018 9:24AM - 9:36AM |
X31.00008: First-principles Investigation of the Dielectric Response of Gold-Silver Alloy Xiao Shen, Yongmei Wang The alloys of gold and silver feature tunable dielectric response with excellent chemical stability and have broad applications in the area of plasmonics. The dielectric constants of such alloys are critical material parameters in the engineering of plasmonic structures and devices. A common practice to obtain the dielectric constants of alloys is to use the mole fraction average of the pure components. This method works in many materials but yields unsatisfactory results for gold-silver alloys. The nature of such discrepancy has yet to be understood. Here we present results from first-principles calculations of gold-silver alloys and unveil the atomistic-scale mechanism that dictates their dielectric response. The results not only elucidate the mystery in the gold-silver alloys but can also be used to guide the design of other metallic alloys for plasmonics applications. |
Friday, March 9, 2018 9:36AM - 9:48AM |
X31.00009: Stability of the BCC Structure in the Mg-Ca Alloy System Guy Skinner, John Moriarty, Eleftherios Andritsos, Anthony Paxton Magnesium and it’s alloys have long suffered from poor formability. The origin of this can be traced back to the HCP structure, which Mg assumes for ambient pressures, since the requirement of five independent slip planes for ductility is generally not satisfied. This has lead to interest in BCC Mg alloys for which, given thermal activation, there are the requisite number of slip planes. Most of the previous work in this regard has focused on Lithium containing alloys. However, we explore the stability and mechanical properties of a BCC Mg-Ca alloy using special quasi random structures and novel GPT alloy pair potentials. In addition, we make calculations of the heat of formation in order to assess the solubility of Ca in the Mg bulk.. |
Friday, March 9, 2018 9:48AM - 10:00AM |
X31.00010: DFT-GIPAW simulations of 27Al NMR spectral parameters in metallic alloys Ary Ferreira, José Rino Among the diverse range of existing alloys, Al-containing intermetallics are of great interest, mainly for structural, oxidation, corrosion, and sulfidation-resistant applications. Due to their diversified crystal chemistry, their atomic-level structural characterization is of great relevance, not only for the industry but also for basic research. In this context, 27Al solid-state NMR experiments have been used for crystal structure validation and also pointed as valuable source of information regarding electronic structure. Nevertheless, the anisotropic nuclear interactions are quite complex in such systems, mainly due to the breaking of the spin-degeneracy of conduction electrons in the presence of an uniform external magnetic field. We report here the use of the GIPAW method for the computation of 27Al NMR spectral parameters in nonmagnetic metallic solids, covering a wide range of isotropic chemical shifts (from about -200 to 1600 ppm). The results achieved demonstrate the possibility to expand the applications of this experimental technique with the aid of first-principles simulations, with deeper insight into nuclear interactions and less speculative assignments. |
Friday, March 9, 2018 10:00AM - 10:12AM |
X31.00011: Optical Properties of Intermetallic Superalloys: An Investigation from Experiment and Theory Erin Curry, Sanjubala Sahoo, Pamir Alpay, Rainer Hebert, Brian Willis, Jie Qi, Jason Hancock We present a combined experimental and theoretical investigation for the optical properties of Ni-based intermetallic superalloys. Using broadband infrared reflectivity and visible-light ellipsometry, we measure the complex frequency-dependent dielectric function and compare it with our findings from density functional based methods. The Ni-based intermetallic superalloy is modeled for various compositions (Ni60Cr25Fe15, Ni75Cr25, Ni) with a randomly distributed face-centered cubic supercell to explore the frequency-dependent dielectric function from the associated intra and interband transitions. We find reasonable agreement between theory and experiment regarding especially the distribution of spectral weight across the energy range <6eV for the superalloy composition which best represents the composition of the sample measured in the experiment. The striking similarities of the modeled and measured Ni60Cr25Fe15 optical functions indicate that complex, disordered systems can be understood using a simple computational scheme. |
Friday, March 9, 2018 10:12AM - 10:24AM |
X31.00012: Observation Laser-induced Transient Melting of Gold Thin Films Tadesse Assefa, Yue Cao, Soham Banerjee, Emil Bozin, Pavol Juhas, Simon Billinge, Sunam Kim, Hyunjung Kim, Changyong Song, Ian Robinson, Sungwon Kim, Dongjin Kim Time-resolved optical laser pump and X-ray/or electron probe techniques opens up an opportunity to look at the dynamical melting of solid state materials which is still one of the grand challenges in ultrafast science. Recent Ultrafast Electron and X-ray Diffraction studies of gold thin films found distinct changes of the melted state with reduced crystalline peak intensity and the rise of a new disorder state after laser excitation. The results were interpreted using two-temperature model and showed the formation of a new state, however, further insights into the local structure of the new disordered state are still lacking. |
Friday, March 9, 2018 10:24AM - 10:36AM |
X31.00013: AlCu Alloyed Thin Films for Perfect Absorbers in a Planar Bilayer Configuration Mariama Rebello Sousa Dias, Chen Gong, Zackery Benson, Marina Leite Metamaterials and metasurfaces present new opportunities for manipulating the optical response at the nanoscale. For instance, single-, double-, and broad-band perfect absorbers have been implemented with a careful design of its subwavelength building blocks. However, the methods of fabrication required are not readily accessible. As an alternative to achieve such optical behavior, we have tuned the optical response of metallic thin films by alloying Al and Cu. In this work, we show that a single-band, omnidirectional, near-unity absorption (> 99%) is obtained for a system composed of Si and AlCu. Moreover, depending on the thickness of the semiconductor layer the absorption can be adjusted at a selected wavelength ranging from the NIR to visible. Additionally, we obtained a dual-band perfect absorber with both peaks presenting absorption > 98%. The results reported here can herald for the design of next-generation electro-optical devices, such as photodetectors, bolometers, and optical filters. |
Friday, March 9, 2018 10:36AM - 10:48AM |
X31.00014: Time-resolved x-ray diffraction of alloy formation in a AuPt multilayer film. Matthew DeCamp, Aaron Loether, Jie Ren, Anthony DiChiara, Karl Unruh Revealing atomic scale motion at picosecond timescales can reveal important features of the energy landscape that dictates structure. In this work, sub-nanosecond time-resolved x-ray diffraction measurements of metallic alloy formation following sub-picosecond optical photoexcitation is presented. Under thses condtions, a Au-Pt multilayer film loses structural coherence in less than 100ps followed by the rapid growth of a new polycrystalline AuPt alloy within 1μs. Comparisons to diffusional mixing models reveals a growth rate four orders of magnitude larger than previous results would suggest. |
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