Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A12: Atomic Structure, Lattice Properties and Phase TransitionsRecordings Available
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Sponsoring Units: FIAP Chair: Yichao Zhang, University of Illinois at Urbana-Champai Room: McCormick Place W-181C |
Monday, March 14, 2022 8:00AM - 8:12AM |
A12.00001: Polymorpism of Group-IV carbides: Structures, (meta)stability, vibrational and electronic properties Matthew C Jankousky, Emily McDonald, Vladan Stevanovic Motivated by the rich polymorphism of elemental carbon and SiC, herein we systematically investigate the space of crystal structures and their metastability for the entire set of group-IV mono-carbides (C, SiC, GeC, and SnC) using an ab-initio random structure sampling methodology. All known structures of elemental C and SiC are correctly identified as metastable polymorphs. Moreover, the only structures found for the studied carbides are the tetrahedrally bonded zinc-blende (s.g. no. 216), wurtzite (s.g. no. 186), and rhombohedral (s.g. no. 160) structures as well as the high-pressure, octahedrally coordinated rocksalt (s.g. no. 225) phase. Though SnC and GeC share the same family of polymorphs as SiC, the metastability of these structures is distinct. For GeC, the rocksalt structure, which is missing in the random sampling, is shown to be dynamically unstable. In SnC all four structures are found, but the phase separated solution is much lower in energy, consistent with the lack of experimental realization of SnC. However, wurtzite SnC is well lattice matched to InN suggesting epitaxial growth as a possible avenue to realize SnC and take advantage of its predicted exceptional electron mobility. |
Monday, March 14, 2022 8:12AM - 8:24AM |
A12.00002: Short-range order in binary Group IV alloys Xiaochen Jin, Shunda Chen, Boxiao Cao, Jifeng Liu, Tianshu Li Group IV alloys based on Si, Ge and Sn have attracted research interest as a potential candidate for mid-infrared photonics due to advantages of Si-compatibility, low-cost, and tunable band gaps. Group IV alloys have been commonly conceived as a random solid solution, but it is unclear how random these alloys truly are. By carrying out extensive DFT-based Monte Carlo sampling, we showed the structures of both GeSn1 and SiSn2 alloys display substantial deviations from random solid solution through a short-range order (SRO). Remarkably, despite their structural resemblance, GeSn and SiSn alloys were found to exhibit very different natures of SRO: In GeSn alloy, the SRO is mainly reflected by solute-solute first-nearest-neighbor repulsion, whereas in SiSn alloy, the SRO carries a more complex form which originates from the competition between solute-solute first- and second-nearest-neighbor repulsion. In both alloys, SRO was further demonstrated to strongly affect electronic structures. Particularly, the predicted band gaps in GeSn alloys with SRO were found to yield an excellent agreement with experiments. Our findings not only demonstrate the significant role of SRO in material properties of binary group IV alloys, but also contribute to new understandings of natures of SRO. |
Monday, March 14, 2022 8:24AM - 8:36AM |
A12.00003: Nuclear Magnetic Resonance investigation of ferroquadrupolar order in TmVO4 Yu-Hsuan Nian, I. Vinograd, T. Greene, Z. Wang, P. Massat, I. Fisher, N. J Curro TmVO4 undergoes structural phase transition from tetragonal to orthorhombic at 2.15K due to a cooperative Jahn-Teller distortion. The electronic ground state of Tm3+ is a non-Kramers doublet which is separated from the first excited state by 54 cm-1. We have performed 51V NMR in a single crystal to investigate critical behavior below and above the ferroquadrupolar transition temperature. We observed strong divergences on the spin lattice and spin spin relaxation rates at the transition temperature, and find that the ordering temperature is suppressed with field along the c-axis. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A12.00004: A Low Temperature Structural Transition in Canfieldite, Ag8SnS6, Single Crystals Tyler J Slade, Volodymyr Gvozdetskyi, John M Wilde, Andreas Kreyssig, Elena Gati, Lin-Lin Wang, Yaroslav Mudryk, Raquel A Ribeiro, Vitalij K Pecharsky, Julia V Zaikina, Paul C Canfield, Sergey L Budko We report the solution growth of single crystals of Ag8SnS6 (Canfieldite) from a Ag-Sn-S melt. On cooling from high temperature, Ag8SnS6 undergoes a known cubic (F-43m) to orthorhombic (Pna21) transition at 460 K. Here, we discover a second structural transition at 120 K (on warming). Single crystal X-ray diffraction shows the low temperature phase adopts a different orthorhombic structure with space group Pmn21 that is isostructural to the room temperature forms of the related compounds Ag8SnSe6 and Ag8GeSe6. The 120 K transition is first-order with large thermal hysteresis. We find the room temperature polymorph can be kinetically arrested into a metastable state by fast cooling to temperatures below 40 K. We lastly compare the room and low temperature forms of Ag8SnS6 with its analogues, Ag8TQ6 (T = Si, Ge, Sn; Q = S, Se), and identify a trend relating the preferred structures to the unit cell volume, suggesting smaller volume favors the Pna21 arrangement. |
Monday, March 14, 2022 8:48AM - 9:00AM Withdrawn |
A12.00005: Optical-phonon-dominated heat transport: a first-principles thermal conductivity study of BaSnS2 Zhi Li, Hongyao Xie, Shiqiang Hao, Yi Xia, Xianli Su, Mercouri G Kanatzidis, Christopher M Wolverton, Xinfeng Tang Materials with low lattice thermal conductivity κL have great potential in thermoelectrics, heat management, and other frontier fields. Combining Boltzmann transport theory with the Allen–Feldman model, we predict a low κL of 0.5 W m−1 K−1 at 850 K in BaSnS2, later confirmed by experimental results. We show that the off-diagonal part of κL contributed by wave-like tunneling phonons becomes pronounced at high temperatures and leads to a deviation of the temperature dependence of κL from T-1 to T-0.76, implying the lattice anharmonicity in BaSnS2. Further analyses indicate over 68% of κL is contributed by optical phonons, owing to their relatively high group velocity. These optical modes are visualized as anti-phase vibrations in BaSnS2 monolayers originating from the unique permutation of SnS3 tetrahedra. By investigating the mode-resolved group velocity, relaxation time, and Grüneisen parameter, we attribute the intrinsic low κL to the soft lattice and the high lattice anharmonicity induced by the Ba–S weak bonding and Sn(II) lone pair electrons. Our study uncovers the microscopic mechanism of optical-phonon-dominated heat transport in BaSnS2 and suggests it worthy of further experimental studies as an intrinsic-low-κL material. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A12.00006: Magnetic Control of Soft Chiral Phonons in PbTe Andrey Baydin, Felix Hernandez, Martin A Rodriguez-vega, Anderson Okazaki, Fuyang Tay, Gary T Noe, Ikufumi Katayama, Jun Takeda, Hiroyuki Nojiri, Paulo Rappl, Eduardo Abramof, Gregory A Fiete, Junichiro Kono PbTe crystals have a soft transverse optical phonon mode in the terahertz frequency range, which is known to efficiently decay into heat-carrying acoustic phonons, resulting in anomalously low thermal conductivity. Here, we studied this phonon via polarization-dependent terahertz spectroscopy. We observed softening of this mode with decreasing temperature, indicative of incipient ferroelectricity, which we explain through a model including strong anharmonicity with a quartic displacement term. In magnetic fields up to 25T, the phonon mode splits into two modes with opposite handedness, exhibiting circular dichroism. Their frequencies display Zeeman splitting together with an overall diamagnetic shift with increasing magnetic field. Using a group-theoretical approach, we demonstrate that these observations are the result of magnetic field-induced morphic changes in the crystal symmetries through the Lorentz force exerted on the lattice ions. Our study thus reveals a novel process of controlling phonon properties in a soft ionic lattice by a strong magnetic field. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A12.00007: Characterization of temperature-induced randomness in the dynamics of vibration Amir Behbahanian, Nicholas Roberts, Jason larkin The nature of the dynamics of vibrations in an amorphous material provides the chance for other modeling approaches such as random matrix theory. This method provides an alternate approach to model materials' evolution in time. So far, the random matrix method applies to amorphous materials due to the random nature of vibrations that stems from the random structure of amorphous materials. This work evaluates the possibility of finding random behavior in crystalline materials at different temperatures and different potential conditions. In our approach, we hypothesis temperature being the source of randomness, and we evaluate the hypothesis by comparing two cases of vibrations in the same material. One of the cases is the time evolution of Aragon under the Lennard Jones potential, and the other case is the same system with added randomness to its dynamics through Brownian dynamics. To support our result, we also utilize the terminology and methods developed to analyze the dynamics of vibrations in amorphous materials to evaluate and characterize the vibrations in the same Argon system at different temperatures and having modified strength of the potential. Our results show changes in the lifetime of the modes with the addition of randomness to the system. The difference between the lifetime of the modes in an Argon system with and without randomness vanished with increasing temperature. This observation is also supported by observing local non-coherent modes with the increase of the temperature, and we found less localization in an argon system having stronger potential. As a result, we concluded that using a method that tunes the randomness can model crystalline materials at high temperatures. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A12.00008: Structural origins of the low-temperature orthorhombic-to-tetragonal phase transition in high-Tc cuprates. Christopher Keegan The La(2-x)Ba(x)CuO4 (LBCO) high-temperature superconductor exhibits a structural phase transition from a low-temperature orthorhombic (LTO) phase to a low-temperature tetragonal (LTT) phase near x = 1/8 doping, which is correlated with a suppression of superconductivity and the concomitant formation of charge density waves. Here we study La2MgO4, which is a structural analog of LBCO. Since La2MgO4 does not possess the strong electronic correlations that give rise to, e.g., the superconductivity observed in the cuprates, we use it to help disentangle structural and electronic mechanisms of the LTO-LTT phase transition. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A12.00009: Multiple anharmonic charge density wave analysis in monolayer Weyl Semimetal SnP. Martin Gutierrez, Maia G Garcia Vergniory, Ion Errea In this work we analyze the stability and CDW phase transitions of Sn4P3 and its potentially exfolliable monolayer SnP. We confirmed the stability of bulk Sn4P3 both using density functional theory (DFT) calculations and synthesizing it experimentally. The experiments confirm the layer structure of the compound, suggesting the structure may be synthesized down to the monolayer by exfoliation or chemical means. Despite the stability of the bulk counterpart, the monolayer presents unstable phonons at Γ, K and M, which may lead to three possible charge density waves. We study the occurrence of these three CDWs by analyzing the phonons with a non-variational treatment of anharmonicity [1,2]. Interestingly, the ground-state structure would be unnoticed without anharmonic effects, which are very strong in the system. All three CDWs lead to metastable insulator phases. Ultimately we performed a symmetry indicators [3,4] based topological analysis, showing how under strain the phase driven by the active phonon in the K is topologically non-trivial. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A12.00010: Design and development of electroluminescent white light emitting diodes using carbon dots as active emitters Manasa Perikala, Asha Bhardwaj Energy conservation has become a major concern globally in today's world and artificial lighting constitutes around ~50% of total energy consumption.Recent advancement in the fabrication of artificial lighting sources include use of semi-conductor quantum dots as active emitters in white light emitting diodes (WLEDs). Semiconductor quantum dots as phosphor material for WLEDs exhibit size-tuneable emissions, high photoluminescence quantum yields, low scattering compared to traditional phosphors. So far quantum dot WLEDs with red green emitting CdSe QDs, CdSe-ZnS QDs, CdS QDs, etc., as phosphor material have been reported in literature. Although WLEDs are fabricated using these dots, they are potentially toxic to be used for indoor and outdoor lighting as they contain highly toxic materials during their fabrication. Further these dots show self-absorption phenomena due to the use of red and green dots in their device structures, affecting the CRI and efficiency of the fabricated device. Henceforth it is ideal to fabricate phosphor using non-toxic materials showing zero self-absorption, high CRIs, high device efficiencies. The emerging carbon dots seems to be an alternative to semiconductor dots for WLEDs due to their wide availability and broad emissive behaviour with least toxicity increasing their potential applications in fabricating white light emitting devices. Moreover, CDs are resistant to photobleaching and photo blinking, show higher luminescence, and large two photon cross section areas, which makes them highly beneficial for applications in fabricating LED sources. Also, photoluminescence properties of carbon dots can be controlled by modifying the size and surface of carbon dots fabricated. This surface modification of CDs enhances the intensity of PL emission from CDs which can have a direct impact on increasing efficiency of WLED fabricated. In this work we report fabrication of WLEDs with carbon dots as active emitters. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A12.00011: Effect of the step-flow growth on defect nucleation in SiC epitaxy by first-principles simulations and machine learning interatomic potentials Senja J Ramakers, Yu Xie, Thomas Eckl, Maximilian Amsler, Boris Kozinsky, Thomas Hammerschmidt, Matous Mrovec, Ralf Drautz SiC is an emerging material for power electronics due to its superior properties, like a wide band gap, compared to conventional Si-based technologies1. Defect-free epitaxial growth remains one of the main challenges in maximizing wafer yield. Stacking faults and triangular defects occur due to the mixing of two competing phases2, called the 3C and 4H polytype with different stacking sequences, and cause leakage currents and device breakdown3. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A12.00012: Low-Energy Photoluminescence Induced by Substitutional Nitrogen in Single-Layer Tungsten Disulfide Qingkai Qian, Lintao Peng, Yuanxi Wang, Anne Marie Z. Tan, Liangbo Liang, Tanushree H. Choudhury, Joan M. Redwing, Alexander A. Puretzky, David B. Geohegan, Richard G. Hennig, Xuedan Ma, Shengxi Huang Defect engineering is an important technique to tailor the electronic and optical properties of two-dimensional materials. By creating defects using remote N2 plasma exposure, distinct low-energy photoluminescence (PL) peak at 1.59 eV is introduced in single-layer WS2. The N2 plasma exposure dose has a critical influence over this PL peak intensity, making it strongest at about 2.0% sulfur deficiencies and vanish at 5.6% or higher sulfur deficiencies. First-principles calculations suggest that this PL peak is caused by the sulfur substitutions by nitrogen. The substitutional nitrogen defect can serve as an isolated artificial atom for single-photon emitters and can be used to monitor the nitrogen p-type doping concentrations. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A12.00013: Molecular Beam Epitaxial Growth and Characterization of GaInSb/GaSb (111) Quantum Wells Siqi Yao, Jianfeng Zhang, Yu-Jiang Dong, Rui-Rui Du Inverted semiconductor InAs/GaSb QWs system represents an archetypical two-dimensional topological insulator, and the strained-layer InAs/GaInSb (001) QWs have been shown to exhibit a large bulk gap comparable to room temperature. There is a current interest to explore the MBE growth of this materials system on other low index planes. The (111) QWs have been given particular attention due to strain-induced piezoelectric effect, which in term may affect the topological properties. As a first step towards the growth of high-quality strained-layer InAs/GaInSb(111) 2D TIs, we have successfully grown the strained-layer GaInSb/GaSb QW on GaAs(111)B substrate.We will present growth optimization and low temperature transport data with a brief discussion |
Monday, March 14, 2022 10:36AM - 10:48AM |
A12.00014: Exploration of the effect of inter-orbital hybridization on lattice instabilities in one-dimensional chains Nassim Derriche, George A Sawatzky, Ilya Elfimov Fermi surface nesting effects have largely been acclaimed as the mechanism resulting in lattice instabilities and the formation of charge and spin density waves as temperature is decreased. These concepts are mainly based on the discontinuities in the charge susceptibility represented by the bands crossing the Fermi energy. In 1D, this results in the familiar Peierls instability for a wave vector equal to 2kf. According to Peierls' work, the ground state of one-dimensional chains of hydrogen atoms at half electron filling is dimerized. In its original form, this argument should apply to other species such as lithium, but ab initio density functional calculations predict that equally spaced chains of this species are not susceptible to lattice instabilities. This is in spite of there being only one band crossing the Fermi energy which as in H is a half filled band in one electron theory. We show that the root cause of this apparent failing of the Peierls model is due to its disregard of the form of the charge carrier wavefunction, notably of the presence of orbital hybridisation. Calculating the charge density susceptibility for these systems while fully taking inter-orbital hybridization into account through a tight binding model leads to an elimination of the divergence usually indicative of a lattice instability in lithium chains. |
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