Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E59: Atomic Structure, Lattice Properties and Phase TransitionsLive
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Sponsoring Units: FIAP Chair: James Rondinelli, Northwestern University |
Tuesday, March 16, 2021 8:00AM - 8:12AM Live |
E59.00001: Control of Plasmons in Topological Systems Zhihao Jiang, Henning Schloemer, Stephan Wolfgang Haas Topological insulators are characterized by non-trivial symmetry-protected topological order which leads to fundamentally novel band structure and electronic states. Topological features also manifest themselves in the collective excitations. For example, localized as well as propagating plasmon modes are observed on the surface of topologically non-trivial systems. In this work, we study plasmonic excitations in a topological system with a partially filled band, focusing on the effects of Coulomb interactions upon manipulating internal degrees of freedom, such as the sub-lattice orbitals. While the symmetry properties of the topological system characterize the electronic wavefunctions over these orbitals, the Coulomb interactions in the system also depend on the real-space configuration of these orbitals. Together, these factors determine the dielectric response function and the dynamical screening in the system. We find that through control of these internal orbitals we can tune the intra- and inter-band screening effect, and ultimately suppress or enhance plasmon dispersions in different energy regimes. We propose simple ideas on how to observe these effects in experiments. |
Tuesday, March 16, 2021 8:12AM - 8:24AM Live |
E59.00002: Solving for a bipolaron bound state in strontium titanate (SrTiO3) Lisa Lin The origin of superconductivity in the doped semiconductor strontium titanate (STO) is not well-understood. Its persistence even at very low carrier densities violates key assumptions of conventional Bardeen-Cooper-Schrieffer (BCS) theory, particularly in that the phonons in this density regime are much faster than the electrons to which they are coupled. The formation of bipolarons, two-electron bound states in a polar medium, serves as a potential electron pairing mechanism beyond the BCS paradigm. Here, the existence of bipolarons in STO is probed using semiclassical analyses and variational calculations to estimate the system’s ground state energy in the weak- and strong-coupling limits of the electron-phonon interaction strength in STO, respectively. It is found that no binding exists in the weak-coupling regime, whereas the strong-coupling regime exhibits strong binding. |
Tuesday, March 16, 2021 8:24AM - 8:36AM Live |
E59.00003: Proton strings and rings in atypical nucleation of ferroelectricity in ice Jorge Augusto Lasave, Sergio Koval, Alessandro Laio, Erio Tosatti Ordinary ice has a proton-disordered phase which is kinetically metastable. Upon doping with KOH at low temperature the transition to ferroelectric (FE) ice takes place, with a mechanism that needs clarification. We introduce a lattice model based on dipolar interactions plus a frustrating term that enforces the ice rule (IR). In the absence of IR-breaking defects, standard Monte Carlo (MC) simulations leave the defect-free ice model in a state of disordered proton ring configurations with the correct Pauling entropy. A replica-exchange accelerated MC sampling enables full equilibration, reaching low-temperature FE order through a well defined first order phase transition. When proton vacancies mimicking the KOH impurities are planted into this IR-conserving lattice, they enable standard MC to work, revealing the kinetics of evolution of ice from proton disorder to partial FE order below the transition temperature. Replacing ordinary nucleation, each impurity opens up a proton ring generating a linear string, an actual ferroelectric hydrogen-bond wire that expands with time. The predicted dependence of FE order fraction upon dopant concentration and quenching temperature agree well with that of real KOH doped ice. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E59.00004: Ultrafast photoexcitation driven non-thermal amorphization of GeTe Liqiu Yang, Subodh C Tiwari, Fuyuki Shimojo, Rajiv K Kalia, Aiichiro Nakano, Priya Vashishta, Paulo S Branicio In this work, we modeled the photoexcitation-driven non-thermal amorphization process in GeTe using nonadiabatic quantum molecular dynamics (NAQMD). Results show that the amorphization of crystalline GeTe occurs at a valence electron excitation threshold of 4%. The photoexcited-induced charge transfer as well as the evolution of excited electronic states is characterized in order to understand the amorphization process. The loss of long-range order of the crystalline structure without fulfilling the Lindemann criterion for melting is achieved by upsetting the Peierls distortion that stabilize the cubic structure of GeTe. That allows for electron-phonon coupling induced large local distortions of Ge-Te bonding leading to collapse of the fragile metavalently bonded crystalline structure. This work provides insights into electronic mechanisms of ultrafast non-thermal amorphization processes induced by intense femtosecond laser excitation of metavalently bonded materials. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E59.00005: Amorphous GexSe1-x and its hierarchical structures by mean of molecular dynamics simulations Francesco Tavanti, Behnood Dianat, Alessandra Catellani, Arrigo Calzolari Amorphous chalcogenides, such as GexSe1-x, have been proposed as good candidates as ovonic switch materials for nonvolatile memories and selectors applications due to their fast switching, endurance and higher crystallization temperature respect to standard GST compounds. The electrical properties of GexSe1-x, as for other chalcogenides, are related to the presence of short- and medium-range structures in the amorphous state. To describe the structure of GexSe1-x in the 0.4-0.6 range at the atomic level, we employed classical molecular dynamics (MD) simulations of large systems and for long timescales allowing the structural rearrangement of the amorphous state at room temperature. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E59.00006: Anisotropic High Carrier Mobilities of One-Third-Hydrogenated Group V Elemental Monolayers Xianli Zhang, Deliang Bao, Wenhan Dong, Jiatao Sun, Shixuan Du Group-VA elemental monolayers, such as antimonene and bismuthene, are predicted to be wide band gap semiconductors. We employ first principles calculations to investigate the atomic structures and electronic properties of one-third-hydrogenated (OTH) group-VA elemental monolayers, that is, OTH-X (X = As, Sb, or Bi). OTH-X exhibit anisotropic electronic and optical properties, such as carrier mobility and light absorbance. Remarkably, OTH-Bi shows an energy band gap inversion induced by external compression, implying a topological phase transition. Furthermore, the carrier mobilities of OTH-Bi for electron and hole along the zigzag direction are on the order of 105 cm2*V−1*s-1 , which is comparable to those of graphene. Our results show that atomically precise functionalization of two-dimensional materials can effectively enhance the intrinsic electrical properties. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E59.00007: A Novel Two-Dimensional material for next generation piezoelectric and thermoelectric applications Yelda Kadioglu, Can Ataca We predicted a new stable monolayer form of SnX3 family which can be extracted from its bulk structure by exfoliation methods. Dynamical and thermal stabilities were confirmed by phonon and temperature dependent molecular dynamic (MD) calculations. The monolayer maintained its stable structure up to 1000 K without significant structural deformation. SnAs3 is a nonmagnetic semiconductor material and possess 0.24 eV indirect band gap value. Spin-orbit interaction did not influence electronic and magnetic properties of the material. Due to atomic orientation, SnAs3 monolayers found to have significant piezoelectric properties. Thermoelectric properties are also conducted using Boltzmann Transport Theory and effects of electronic and phononic contributions are considered for evaluating thermal conductivity. This manuscript details the stability, electronic, magnetic, piezoelectric and thermoelectric properties of a novel two-dimensional material. We believe that SnAs3 is possible candidate for next generation device applications. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E59.00008: Pressure-Induced Insulator-Metal Phase Transition in Si2Te3 from First-Principles Calculations Romakanta Bhattarai, Xiao Shen Silicon telluride (Si2Te3) is a layered two-dimensional p-type semiconductor with unique structural variability arising from the presence of silicon dimers filling two-third of the allowed sites with different orientations. A recent experiment reported that the material undergoes an insulator-metal phase transition under hydrostatic pressure at 9.5 GPa. Using the evolutionary algorithm combined with the first-principles density functional theory calculations, we identify two metallic phases of Si2Te3 to account for the observation. The calculated insulator-metal transition pressures agree very well with the experimental results. Furthermore, we find that the external hydrostatic pressure causes the semiconducting phase to undergo an indirect-direct-indirect band gap transition. Such pressure-induced gap transitions could be beneficial for potential applications of the material. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E59.00009: Changing soft mode dynamics of the polar metal EuTiO3 with photodoping Daniel Hickox-Young, Alon Ron, Kaveh Ahadi, Danilo Puggioni, Omar Mehio, James M Rondinelli, Susanne Stemmer, David Hsieh EuTiO3 (ETO) is a paraelectric (PE), antiferromagnetic (AFM) insulator under ambient conditions, but can be driven to a ferromagnetic (FM), ferroelectric (FE) state under sufficient tensile strain—achievable by using DyScO3 (DSO) as a substrate. First principles simulations of ETO on DSO indicate that the FE order is disrupted under photodoping. The free electrons generated by photodoping occupy Ti d-states, perturbing the Ti-O bond that drives the FE phase transition. In experiment, an initial reduction in polar order for low photodoping concentrations is observed, but this reduction saturates under increasing photodoping at a non-zero polar amplitude. Thus, at high doping levels, strained EuTiO3 behaves like an intrinsic polar metal, exhibiting a polar distortion which is insensitive to changes at the Fermi level. This transition from doped ferroelectric to polar metallic behavior implies a never-before-seen change in distortion character under doping. We show first principles evidence of changes in the TiO6 displacement patterns under doping and discuss several hypotheses which may explain this new phenomenon. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E59.00010: Investigating Local Disorder in ZnSnN2 with X-ray Absorption Spectroscopy Celeste Melamed, Moira K Miller, Jacob Cordell, Rekha Schnepf, Alyssa Livingood, Linda Pucurimay, Jie Pan, Karen Heinselman, Dennis Nordlund, Stephan Lany, Eric Toberer, Steven Christensen, Adele Tamboli In this work, we investigate the local bonding environment in sputtered ZnSnN2 thin films using X-ray absorption near-edge spectroscopy (XANES). ZnSnN2 has recently shown promise for photovoltaic applications, offering potentially groundbreaking optoelectronic properties with the use of cation site disorder to tune the bandgap. However, questions remain about the connection between local coordination environment and long-range disorder in ZnSnN2. In particular, it has been predicted that different types of local disorder may exist, but these are difficult to distinguish. Oxygen incorporation has also been observed to impact optoelectronic properties, but its bonding structure has not been studied. Here, we probe atomic environment in combinatorial ZnSnN2 samples with N and O k-edge XANES. Prominent spectral features are compared to partial density of states calculations and reference compounds. Finally, XANES results are related to structural characterization in order to understand the mechanisms behind cation disorder and off-stoichiometry. This work provides a new understanding of the local environment in ZnSnN2 and demonstrates the use of XANES to probe disorder in II-IV-Ns. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E59.00011: Structural stability of monolayer GaSe with trigonal-antiprismatic structure studied by first-principles calculations Hirokazu Nitta, Takahiro Yonezawa, Antoine Fleurence, Yukiko Yamada-Takamura, Taisuke Ozaki Gallium Selenide (GaSe) is a layered post-transition metal monochalcogenide with a 2 eV band gap. We have recently succeeded in growing epitaxial GaSe(0001) thin films on Ge(111) substrates by molecular beam epitaxy (MBE) and revealed that a new polymorph of GaSe with trigonal-antiprismatic (AP) structure exists near the GaSe(0001)/Ge(111) interface [1]. In this study [2], the structural stability and electronic states of AP-phase GaSe monolayer were studied by first-principles calculations. While conventional trigonal-prismatic (P)-phase is the most stable phase at equilibrium lattice constants, the AP-phase GaSe become more stable than the P-phase GaSe as the in-plane tensile strain increases. In contrast to MoS2 for which the P- and AP-phase (octahedral) MoS2 have very different band structures, P- and AP-phase GaSe have similar band structures. This is due to the absence of changes in the angles between bonds between nearest neighbors. The difference in band structure and optical properties due to the differences in crystal symmetry will be discussed. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E59.00012: Phase Stability and Thickness-Dependence of Properties in Silicon Nanomembranes Under Pressure Joel Ambriz Ponce, William Parker Elemental silicon is a material with a wide range of applications from the electronic to the optical to the mechanical. Recent advances in growth methodology have achieved the synthesis of flat, nanometer-scale thickness membranes. To understand and predict the energetic and mechanical properties of these membranes in contrast with bulk crystalline silicon, we model silicon nanomembranes at the electronic level in an atomistic model using density functional theory at varying levels of exchange-correlation functional. With a slab model for the nanomembrane, we investigate the pressure-based transition from the ambient-condition diamond phase to the higher-pressure beta-tin phase under out-of-plane uniaxial and in-plane biaxial compression. In addition to calculating the transition pressure and volume from one phase to the other under increasing slab thickness, we also investigate the change in elastic, electronic, and vibrational properties of each individual phase with slab thickness, aiming to make multiple experimentally testable predictions. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E59.00013: Far Infrared Reflectance Spectroscopy of High Entropy Rocksalt Structure Oxides Tahereh Afsharvosoughi, David Crandles A high entropy oxide is formed by a random distribution of metal atoms amongst ordered oxygen atoms in a crystal lattice. Since in high entropy systems one is dealing with a supercell instead of a unit cell, one cannot simply find the number of optical modes by knowing the number of atoms in the unit cell. In this experimental work the far infrared reflectance of a rocksalt structure high entropy oxide (NiCoMgZnCu)O for both single phase prepared by air quenching the mixture of five binary oxides from 1100oC and a multiphase sample were measured between 50 cm-1 to 1000 cm-1 and temperatures between 4 and 300K in order to study the phonon vibrational modes and the effect of the antiferromagnetic transition on the modes. The far infrared reflectance showed one optical mode with a sideband which resembles the FIR reflectance of diatomic rocksalt compounds. The multiphase spectrum was different and it behaves qualitatively as the combination of FIR reflectance of all constituents. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E59.00014: Raman Scattering in Medium and High Entropy Rocksalt Oxides David Crandles, Tahereh Afsharvosoughi, Maureen Reedyk The Temperature Dependence (4-300K) of the Raman Scattering spectrum of various polycrystalline single phase rocksalt high or medium entropy oxides has been measured. The samples were prepared by mixing equimolar amounts of either four or five of the binary oxides (MgO,CoO,NiO,CuO,ZnO) and sintering at or above 1000oC followed by air-quenching. The samples can be classified as either high entropy oxides (5-HEO) for mixtures of all five binary oxides, or medium entropy oxides (4-MEO) for mixtures of equimolar amounts of four binary oxides depending on the value of mixing entropy. Xray diffraction (XRD) indicated that the majority of samples were single fcc phase except for the 4-MEO (-Ni). The samples all showed similar Raman scattering spectra containing three main peaks near 545, 1096 and 1650 cm-1 with satellite shoulders on the low frequency tail of the main peaks. The Raman spectra will be interpreted in light of the antiferromagnetic transitions exhibited by all the samples. |
Tuesday, March 16, 2021 10:48AM - 11:00AM Not Participating |
E59.00015: First-principles study of Si and O co-doped band gap opening of TiN Jia Shi, Duy Le, Talat S. Rahman Experimental observations suggest that Si doping could induce semiconducting behavior in metallic TiN. We present here results of density functional theory based calculations of the band structure for the TiN with homogeneous doping using Si dopant (Ti is substituted by Si) and O dopant (N is substituted by O or O atoms are at the interstitial positions) to explain the above metal-insulator transition. We find that 12.5% Si dopant together with O atoms at the interstitial sites () induces a semiconducting character. In this structure, 12.5% Ti atoms are substituted by Si and that there are two types of interstitial O atoms: one forming Si-O bond and the other not. The indirect band gap is calculated to be about 0.5 eV. Our results show that the co-effect of interstitial O and Si dopants plays an important role in inducing metal to semiconductor behavior of TiN. |
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