Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C46: 4d/5d Transition Metal Systems -- Chalcogenides and NonoxidesFocus
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Sponsoring Units: DMP Chair: Janice Musfeldt, Univ of Tennessee, Knoxville Room: BCEC 212 |
Monday, March 4, 2019 2:30PM - 3:06PM |
C46.00001: Electrical and Magnetic Properties of PdSb2 and PtBi2 with Multiple Band Degeneracy Invited Speaker: Rongying Jin The discovery of topological properties in condensed matter started a new era of physics. Many fermionic particles and phenomena predicted in high energy physics are now experimentally observed in topological materials such as Dirac, Weyl, and Majorana particles. Their nontrivial topology results from crossings of conduction and valence bands. Depending on crystal symmetry, such crossings can result in degeneracy (g) with g = 2, 3, 4, 6, and 8. It is known that g = 2 corresponds to Weyl fermions, and g = 4 corresponds to Dirac fermions. The cases of g = 3, 6, and 8 are of particularly interesting as they can only be found in condensed matter systems, having no high energy analogues as constrained by Poincare symmetry. In this talk, I will present our experimental investigations on a 4d compound PdSb2 with g = 6, and a 5d compound PtBi2 with g = 3. By analyzing both the de Haas-van Alphen and Shubnikov-de Haas oscillations observed in these compounds, we obtain topological properties of the bands. The implications of these findings will be discussed. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C46.00002: Confirmation of Semiconducting Behavior in TaIrGe Eteri Svanidze, M Bobnar, I Antonyshyn, Markus Koenig, O Sichevych, U Burkhardt, F Wagner, Yuri Grin Despite being exclusively composed of metallic elements, the half-Heusler compound TaIrGe has been predicted to be a semiconductor with a large indirect gap. Several experimental results, however, have shown metallic behavior. This discrepancy between theoretical prediction and experimental observation is assumed to be due to difficulties in material synthesis. Specifically, the presence of several neighboring phases prevents the synthesis of TaIrGe in single-phase form. With that in mind, we implement focused-ion-beam structuring to polycrystalline TaIrGe. This work does not only provide evidence for intrinsic semiconducting behavior of TaIrGe, but also serves as the first example of selective domain structuring in a polycrystalline material. This novel approach gives a rare opportunity to access materials that cannot be synthesized in single-phase form, sparing costly and time-consuming synthesis efforts, which are frequently futile. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C46.00003: Structural and Physical Properties of Ir3Sn7-xMnx Single Crystals Smita Speer, Hong Chang, Xin Gui, Madalynn G. Marshall, Weiwei Xie, Rongying Jin Transition-metal stannides are known to exhibit strong d-p hybridization, leading to narrow - band gap semiconductors. We have successfully grown Ir3Sn7-xMnx single crystals using the flux method. Single crystal x-ray diffraction refinement indicates that Ir3Sn7-xMnx forms a cubic structure (space group Im3m), and the dopant Mn occupies the Sn site. For x = 0.1, the electrical resistivity shows metallic behavior and can be described by ρ = ρo + aT2 + bT between ~22 K and 300 K. An upturn is observed below 22 K, which is due to an antiferromagnetic (AFM) transition as reflected in the magnetization. Unexpectedly, the application of magnetic field results in negative magnetoresistance below the AFM transition. The effect of Mn doping will be discussed. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C46.00004: In-situ Electron Microcopy Observation of Phase Transitions in Bulk IrTe2 Zhen Wang, Guixin Cao, Zhenyu Zhang, Myung-Geun Han, Lijun Wu, Yimei Zhu, Rongying Jin, E Ward Plummer Transition-metal dichalcogenide IrTe2 has attracted extensive attention because of its intriguing structural transitions, abnormal resistivity, and superconductivity. While it forms a trigonal phase at room temperature, the structure below the phase transition at 280 K is is still in debate. With in-situ transmission and scanning transmission electron microscopy (STEM), we study the phase transitions of IrTe2 single crystal from room temperature down to 20 K. The electron diffraction and imaging results show that IrTe2 below 280 K is phase separated, with the coexistence of the well-characterized 5 × 1 × 5 phase, an intergrowth phases with multiple modulated vectors, and the remaining trigonal phase. The 5 × 1 × 5 phase is present down to 20 K, but we never observe the 6 × 1 × 6 or 8 × 1 × 8 phase previously reported. The valence states of IrTe2 for different phases have been investigated by electron energy loss spectroscopy. A clear picture of the temperature-dependent structural evolution of bulk IrTe2, which is essential to understand the unique electric and magnetic behaviors, will be presented. |
Monday, March 4, 2019 3:42PM - 4:18PM |
C46.00005: Synthesis and properties of nanotubes from “misfit” compounds Invited Speaker: Reshef Tenne Misfit layered compounds (MLC) of the form (MX)1+yTX2 (M=Pb, Sn, rare earth, etc.; X=S,Se,Te; T=Sn, Ta, V, etc.) are known since about 50 years and have been studied by various groups. They are made of an alternating lattice made of one layer of a distorted cubic (orthorhombic) sublattice, like PbS (MS), and hexagonal/octahedral lattice of, e.g. SnS2 or NbS2 (TS2) in a periodic arrangement (denoted as MS.TS2 for brevity). Van der Waals forces hold the MX and TX2 layers together, as well as polarization forces which emanate from partial charge transfer from the MX to the TX2 units. Modern techniques allow synthesizing more complex superstructures from the MX and TX2 sublattices. In many cases, the unit length of the two sublattices coincide along the directions b&c and is incommensurate along a. The lattice mismatch between the MX and TX2 sublattices is known to lead to the formation of microscopic cylindrical crystals for many years. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C46.00006: Generalization of de Gennes factor for the strong spin-orbit coupled systems. Hoshin Gong, Kyoo Kim, Sungdae Ji, Bongjae Kim, Byung Il Min The magnetic exchange interaction parameters of magnetic systems can be obtained from the consideration of energetics within density functional theory (DFT)-based approaches. Spin Hamiltonians, such as the Heisenberg model, are mainly used to fit the various total energies of magnetic configurations obtained from DFT band calculations, which can be directly compared to the experimental findings including spin-wave dispersions. However, for the strong spin-orbit coupled systems, these approaches often fail and predict wrong energy scales compared to the experimental values due to the entanglement of spin and orbital moments. By including the generalized de Gennes factor, which connects the spin and orbital moments to the total moment, we have found that the better description of exchange interaction parameters can be obtained for the strong spin-orbit coupled systems. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C46.00007: A Non-Perturbative, Variational Technique of Calculating RIXS Spectral Response Functions Krzysztof Bieniasz The field of strongly correlated electrons, and in fact condensed matter physics in general, makes heavy use of spectroscopic experiments to pry into the intricate details of the physical properties of solids. In order to explain the spectra measured in such an experiment a theoretical calculation has to be provided, often relying on some effective model of the physical system under consideration. To explain phenomena such as high-Tc superconductivity in cuprates or exotic magnetic and orbital phases in manganites, a wide range of spectroscopic measurements are performed, each requiring a different setup and apparatus. Among them, RIXS is a prominent technique which allows one to probe different degrees of freedom of a system with precise control over electron transitions. Our aim is to develop a simple yet accurate standard theoretical tool for calculating RIXS response functions, relying on the non-perturbative, variational (momentum average) approximation to calculate the relevant propagators. This approach should bridge between the exact diagonalization of small clusters vs. perturbative expansion techniques, which until now have dominated the theory of RIXS. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C46.00008: Thermoelectric studies of Ir1-xRhxTe2 (0 ≤ x ≤ 0.3) Yu Liu, Hechang Lei, Kefeng Wang, Milinda Abeykoon, John Warren, Emil Bozin, Cedomir Petrovic We present the thermal transport properties of Ir1-xRhxTe2 (0 ≤ x ≤ 0.3) alloy series where superconductivity emerges as the high-temperature structural transition (Ts) is suppressed. The isovalent Rh substitution in Ir1-xRhxTe2 results in a slight reduction of lattice parameters and in an increase of number of carriers per unit cell. Positive thermopower S(T) values for all samples indicate the hole-type carriers. The decrease of S(T) in pure IrTe2 (x = 0) at Ts implies that dimer formation is related to partial localization of hole-type carriers below the structural transition. Phonon-related thermal conductivity in pure IrTe2 (x = 0) features a broad maximum around (50 – 60) K, which is significantly suppressed with Rh substitution. This is mostly contributed by the Rh/Ir doping disorder enhanced point defects scattering. Weak-coupled BCS superconductivity in Ir0.8Rh0.2Te2 that emerges at low temperature (Tczero= 2.45 K) is most likely driven by electron-phonon coupling rather than dimer fluctuations mediated pairing. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C46.00009: Magnetic Domains in the Strongly Correlated Weyl Semimetal Candidate CeBi Nathan Drucker, Yu Liu, Christian Matt, Harris Pirie, Na Hyun Jo, Brinda Kuthanazhi, Sergey L. Bud'ko, Paul C. Canfield, Jennifer Hoffman Weyl Fermions can arise from Dirac semimetals when the degenerate massless states are split by broken time-reversal symmetry into two bands with opposite chirality. Recently, such states have been predicted in the strongly correlated cerium monopnictides, which develop band inversion as spin orbit coupling increases, and are known to host complex magnetic phase diagrams. Thus cerium monopnictides are ideal materials for studying the interplay of magnetism and topology. Here, we use spin-polarized scanning tunneling microscopy to map the magnetic phases of CeSb and CeBi on the atomic scale. We find distinct magnetic domains with differing spin periodicities, separated by abrupt domain walls. Furthermore, we observe quasiparticle scattering from the domain walls and defects in both materials. Control of these magnetic phases in cerium monopnictides provides the possibility of tuning the key energy scales and momentum splitting of Weyl fermions. |
Monday, March 4, 2019 5:06PM - 5:18PM |
C46.00010: Probing band topology of Weyl-Kondo semimetal candidates CeSb and CeBi by quasiparticle interference imaging Yu Liu, Christian Matt, Harris Pirie, Nathan Drucker, Na Hyun Jo, Brinda Kuthanazhi, Sergey L. Bud'ko, Paul Canfield, Jennifer Hoffman Topological materials are characterized by strong spin-orbit coupling and bulk band inversion, leading to protected surface states with momentum-locked spin or chirality. Meanwhile, Kondo systems often host rich magnetic phase diagrams because of their strong electron correlations. Materials with both strong spin-orbit coupling and strong electron correlations are predicted to host even more intriguing topological properties. Here we use scanning tunneling microscopy (STM) and quasiparticle interference (QPI) to image the band structure of the predicted Weyl-Kondo candidates CeSb and CeBi. We probe the dispersion of Ce p and d bands, and identify two accidental crossings, one below and one above the Fermi level. We search for topological surface states, by imaging their scattering from atomic defects and magnetic domain boundaries. |
Monday, March 4, 2019 5:18PM - 5:30PM |
C46.00011: Evidence for a purely anionic charge density wave transition in LaAgSb2 Ashish Chainani, Jung-Han Li, Amol Singh, Yen-Fa Liao, Yen-Yi Chu, Ku-Ding Tsuei, Di-Jing Huang, Chia-Nung Kuo, Chin Shan Lue We study the electronic structure of LaAgSb2, using bulk-sensitive temperature(T)-dependent (20 K – 220 K) Hard X-ray photoemission spectroscopy (HAXPES). LaAgSb2 exhibits two CDW transitions, one below T1= 207 K along the crystallographic a-axis, followed by a second CDW transition below T2= 186 K along the c-axis. Recent studies have identified a Dirac-cone band dispersion and nested Fermi surfaces at T = 16 K, but T-dependent measurements were not reported. We use HAXPES to investigate T-dependent changes in the electronic states of La, Ag and Sb in order to identify states responsible for the CDW transition in LaAgSb2. HAXPES core level measurements show that the La 3d and Ag 3d core-levels show negligible changes across the CDW transitions. In contrast, Sb 3d core levels show a clear well-separated satellite formation below T1, and the spectral intensity of the satellite progressively increases on lowering the temperature below T2. The T-dependence of the Sb 3d satellite feature suggests a second order transition, consistent with the known BCS behavior of T-dependent superlattice reflections by x-ray diffraction. The results indicate a purely anionic character CDW transition, with no direct involvement of the La and Ag cationic derived states in the CDW transition. |
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