Bulletin of the American Physical Society
2018 Joint Fall Meeting of the Texas Sections of APS, AAPT and Zone 13 of the SPS
Volume 63, Number 18
Friday–Saturday, October 19–20, 2018; University of Houston, Houston, Texas
Session E02: Condensed Matter Physics I |
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Chair: Oomman Varghese, University of Houston Room: Science and Engineering Classroom (SEC) 102 |
Friday, October 19, 2018 4:15PM - 4:27PM |
E02.00001: Mott transition revealed by coherent phonons in a film of VO2/AlN/Si Hyun-Tak Kim Vanadium dioxide VO2 with a metallic electronic structure of 3d1 is an insulator below Tc=340 K and undergoes the insulator-metal transition(IMT) and the structural phase transition(SPT) near Tc. It has two substructures of zigzag chain and the charge density wave (CDW) with repeatedly a long and a short distance between two atoms, induced by the structural distortion ; this is called M2 phase. The CDW undergoes the Peierls IMT and is accompanied with the SPT, while in the zigzag chain structure, the Mott transition caused by melting of electron correlation occurs. Therefore, it is so difficult to discover the Mott transition. We had successfully deposited the strained VO2/AlN/Si films with a large difference between the IMT and the SPT[1] and observed the monoclinic metal phase without the SPT in the M2 phase through analyzing of the temperature dependence of the coherent phonons measured by a high speed femtosecond system [2]. We explain the monoclinic metal phase using the transport data of Hall effect and the impurity-driven IMT[3]. [1] APL Materials 4, 026101; [2] Scientific report 7, 16038; [3] J. Phys.: Condens. Matter. 28, 085602. |
Friday, October 19, 2018 4:27PM - 4:39PM |
E02.00002: A novel way to synthesize hydrogen incorporated palladium nanoparticles in one-step for hydrogen storage: A combined experimental and DFT study Sajib K Barman, Rakesh P Chaudhary, Muhammad Nurul Huda, Ali R Koymen In this study, a one-step method is presented for storing hydrogen in palladium nanoparticles. The palladium nanoparticles are synthesized by a plasma discharge between Pd electrodes in the cavitation field of toluene. The hydrogen is extracted from toluene and incorporated in plasma generated palladium nanoparticles directly. It was found that the experiment time has a direct effect on the particle size and lattice expansion. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) measurements show that the particle size and lattice expansion increase with experimental time. This effect of experiment time on the particle size and the lattice spacing were investigated by both experimental and computational studies using density functional theory (DFT). The methodology adopted in this synthesis process provides rapid reaction rate, ability to form very small nanoparticles with narrow size distribution and hydrogen extraction from the solvent for direct storage in the Pd nanoparticle lattice. |
Friday, October 19, 2018 4:39PM - 4:51PM |
E02.00003: Ultrafast nonlinear optical processes in CH3NH3PbI3 hybrid perovskite Alex Zakhidov, Eric Welch, Mehedhi Hasan, Dmitry Lyashenko, Petr Obraztsov Methylammonium lead iodide (MAPI) is a benchmark hybrid organic perovskite material, which is used for the low-cost, printed solar cells with over 23% power conversion efficiency. Yet, the nature of light-matter interaction in MAPI as well as the exact physical mechanism behind device operation is currently debated. Here we report room temperature, ultrafast photocurrent and free-space terahertz (THz) emission generation from unbiased MAPI thin films induced by 150 fs light pulses1. Polarization dependence of the observed photocurrents is consistent with the Bulk Photovoltaic Effect (BPVE) caused by a combination of injection and shift currents. We believe that this observation of can shed light on low recombination, and long carrier diffusion lengths due to indirect bandgap. Moreover, ballistic by nature shift and injection BPVE photocurrents may enable third generation perovskite solar cells with efficiency that exceed the Shockley–Queisser limit. Our observations also open new venues for perovskite spintronics and tunable THz sources. [1]. P.A. Obraztsov, et al., Comm. Physics 1, 14 (2018).
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Friday, October 19, 2018 4:51PM - 5:03PM |
E02.00004: Investigation of Enhanced Superconductivity in the FeSe/SrTiO3 System Samira Daneshmandi, Yanfeng Lyu, Hanming Yuan, C. W. Paul Chu The complex superconducting structure of the single-layer FeSe with Tc above 50 K by Q. Y. Wang et al. in 2012 is consistent with the complex interaction between electron-phonon couplings and doping the charge carriers. It is important to discover the nature of the superconducting state observed in the single-layer FeSe in order to design and manufacture higher Tc superconductors. Atomically flat thin films of monolayer and multilayer FeSe have been grown on SiC and SrTiO3 substrates by molecular beam epitaxy (MBE). By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the temperature criterion for layer-by-layer growth of epitaxial FeSe films. A systematic study of the interfacial properties has clarified the essential roles of the substrate in realizing the high-Tc superconductivity, probably via interface-induced electron-phonon coupling enhancement and charge transfer. Motivated by the high Tc of monolayer FeSe on SrTiO3, we carried out systematic annealing on a 3D superlattice FeSe-TiO2 at temperatures between 450 and 700 º C. An unknown transition has been observed above 30 K, which is comparable with the reported Tc for the monolayer FeSe; however, additional measurements are still needed to confirm its origin. |
Friday, October 19, 2018 5:03PM - 5:15PM |
E02.00005: Investigation on the reported superconductivity in intercalated black phosphorus Hanming Yuan, Liangzi Deng, Bing Lv, Zheng Wu, Ze Yang, Sheng Li, Shuyuan Huyan, Yizhou Ni, Jingying Sun, Fei Tian, Dezhi Wang, Hui Wang, Shuo Chen, Zhifeng Ren, C. W. Paul Chu Superconductivity intrinsic to the intercalated black phosphorus (BP) with a transition temperature Tc of 3.8 K, independent of the intercalant, whether an alkali or an alkaline earth element, has been reported by R. Zhang et al. (2017). However, the reported Tc and the field effect on the superconducting (SC) transition both appear to be similar to those for the pure Sn, which is commonly used for BP synthesis under the vapor transport (VP) method. We decided to determine if a minute amount of Sn is present in the starting BP and if it is the culprit for the small SC signal detected. EDS results confirmed the existence of Sn in the starting BP purchased from the same company as in R. Zhang et al. We have reproduced the SC transition at 3.8 K in Li- and Na-intercalated BP that contain minute amounts of Sn when prepared by the VP method but not in BP that are free of Sn when prepared by the high-pressure method. We therefore concluded the SC transition reported by R. Zhang et al. is associated with the Sn but not intrinsic to the intercalated BP crystals. |
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