Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session S27: Thermodynamic and Transport Properties |
Hide Abstracts |
Sponsoring Units: FIAP Chair: Raphael Hermann, Oak Ridge National Lab Room: 404 |
Thursday, March 5, 2020 11:15AM - 11:27AM |
S27.00001: Charge Scattering Mechanisms in shallow InAs quantum wells Elena Cimpoiasu, Matthew J. Fox, Shawn Mack, Joseph A. Christodoulides, Brian R Bennett We studied the charge scattering mechanisms present in In0.2Al0.8Sb/InAs/Al0.8Ga0.2Sb wells placed in close proximity to the surface of the heterostructures, at depths from 7 nm to 15 nm. The heterostructures were either unintentionally-doped, doped from below the channel or from above the channel. Measurements of sheet and Hall resistances were performed at T = 2K in variable magnetic field and under illumination with wavelengths of 400 nm up to 1300 nm. The charge density dependencies of the Hall mobility and quantum scattering time were used to infer the dominant mechanisms. We found that the transport quality of the sample is dominated by bottom interface roughness, and that reducing the asymmetry of the potential well results in improved charge transport as the scattering of interface roughness is reduced. This is, however, detrimental to the strength of spin-orbit coupling and to spin-based applications of these materials |
Thursday, March 5, 2020 11:27AM - 11:39AM |
S27.00002: Transport properties of exfoliated GaTe thin flakes Wenkai Zheng, Justin Felder, Zachary Bryce Goraum, Gregory McCandless, Julia Chan, Luis Balicas Metal mono-chalcogenide(MMCs), such ad GaS, GaSe, InSe, and GaTe, have recently attracted much attention due in part to the evolution of their direct bandgap as a function of the number of layers. Although intrinsic MMC is nonmagnetic, a recent first principle calculation [1] predicts a Stoner-type magnetic instability that leads to the formation of a half-metallic and hence ferromagnetic ground state, which would make these materials interesting for spin transport or applications in spintronics. Here we discuss the temperature-dependent response of Field-Effect Transistors fabricated from GaTe single-crystals grown via a flux method, and measured through two and foru-terminal configurations. We will also discuss the evolution of the Hall effect as a function of the temperature. |
Thursday, March 5, 2020 11:39AM - 11:51AM |
S27.00003: Electronic Properties of Bismuth Iodide (Bi4I4) Thin Films Yulu Liu, Ruoyu Chen, Sheng Li, Xiaoyuan Liu, Takashi Taniguchi, Kenji Watanabe, Bing Lv, Fan Zhang, Chun Ning Lau Due to the gapless conductive surface states which are protected against perturbations, topological insulator materials have attracted much attention in this field. Bi4I4 is a quasi-one-dimensional van der Waals material, and its beta phase has been revealed by angle-resolved photoemission spectroscopy to be a topological insulator, thus offering a new platform for exploring topological phases. To date, all prior works on Bi4I4 are based on the bulk material. Here we report transport measurements of thin Bi4I4 films that are mechanically exfoliated Bi4I4 from bulk crystals. Devices in both alpha and beta phases are characterized. Their gate-tunable resistance demonstrates surface-dominated transport, which is further supported by the observation of weak antilocalization in magnetic fields. Moreover, the temperature behavior in b-Bi4I4 suggests that the inelastic scattering process at low temperature is dominated by the electron-electron interaction. |
Thursday, March 5, 2020 11:51AM - 12:03PM |
S27.00004: Tunneling Two-Level Systems in Amorphous Silica Thin Films Thomas Dauer, Manel Molina-Ruiz, Matthew Abernathy, Thomas Metcalf, Xiao Liu, Frances Hellman Amorphous silica (silicon dioxide) is one of the strongest glass formers known, and silicate glasses are by far the most widely produced for applications. Liquid-quenched silica shows tunneling two-level system density, as probed by low-temperature specific heat and internal friction, in the so-called universal glassy range observed for nearly all amorphous materials. We present low-temperature (down to 300 mK) specific heat and mechanical loss measurements on silica thin films grown at temperatures from 60 to 800 °C by e-beam evaporation. Results indicate that silica grown near room temperature shows TLS density, extracted from cryogenic specific heat, above the universal range. The mechanical loss, though high, is still within the universal range, and falls to the level of bulk silica as the growth temperature is increased to 800 °C. This is consistent with the observed increase in atomic density of approximately 10% as the growth temperature is raised 60 to 800 °C. These results are compared to previous work on amorphous silicon and tantala, with attention drawn to the somewhat unusual relative change of the sound velocity with temperature and how this changes systematically with growth temperature for the silica films. |
Thursday, March 5, 2020 12:03PM - 12:15PM |
S27.00005: Origin of Two-Level Systems in Amorphous Silicon Manel Molina-Ruiz, Yaniv J Rosen, Thomas Dauer, Hilary C Jacks, Matthew Abernathy, Thomas Metcalf, Xiao Liu, Jonathan L DuBois, Frances Hellman Amorphous silicon shows anomalous properties at low temperatures due to two-level systems, which affect both mechanical and electromagnetic oscillators. However, it is unclear whether the two-level systems responsible for these effects are the same. We performed mechanical and dielectric loss measurements of amorphous silicon films grown by electron beam deposition. Samples grown at 425 °C show a large reduction of mechanical loss and a mild reduction of dielectric loss compared to those grown at room temperature. Results indicate mechanical loss is related to mass density, while dielectric loss is to dangling bond density. Moreover, mechanical loss results show lower loss per unit volume for thicker films, while dielectric loss results show lower loss per unit volume for thinner films, suggesting an underlying structural and differential origin for both types of energy dissipation processes. Additionally, specific heat measurements show that the density of two-level systems extends far above the well-known glassy range, indicating that some interactions play a crucial role in creating the universal values of mechanical losses at low temperatures. |
Thursday, March 5, 2020 12:15PM - 12:27PM |
S27.00006: Electrical Transport in Chemically Exfoliated LixCoO2 in 2D Nanoflake Form Kyle Crowley, Kevin Pachuta, Santosh kumar Radha, Halyna Volkova, Alp Sehirlioglu, Walter Lambrecht, Marie-Helene Berger, Xuan Gao Layered oxides possess various novel electronic and magnetic phases, many of which remain either unexplained or continually debated. LixCoO2 is one such material; one of the most commonly used cathode materials in rechargeable batteries, this oxide exhibits a rich landscape of properties, with many aspects still not fully understood. LixCoO2 contains electrostatically stabilized layers, making it difficult to study in its few-layer, single-crystal form. Herein, a two-step process is utilized to chemically delithiate LixCoO2 in the range 0.3<x<0.8. LixCoO2 is then chemically exfoliated, producing nanoflakes 5-100nm thick. Electrical characterization of these individual nanoflakes reveals an insulating behavior upon contact formation, and suppression of metallic tendencies in the low-lithium range (x<0.75), likely due to termination effects of the surface lithium plane. Additionally, an anomaly in the temperature dependent resistance is observed in flakes of specific lithium content, indicating that this fabrication method is suitable for studying charge ordering phenomena in LixCoO2. This technique offers potential for exploring LixCoO2 in its two dimensional form, which has not been reported for single crystals to date. |
Thursday, March 5, 2020 12:27PM - 12:39PM |
S27.00007: Diamagnetic Susceptibility, Disorder, and Linear Magnetoresistance in Ag2-δTe Ian Leahy, Peter Siegfried, Harold Schnyders, Minhyea Lee The origin of linear magnetoresistance in Ag2-δTe has historically sparked debate between several intrinsic and extrinsic mechanisms. We investigate the magnetotransport properties of the narrow-gap semiconductors Ag2-δTe as a function of silver deficiency in order to quantify the role of disorder on their observed linear magnetoresistance. Built on our earlier work [1], we study the temperature and field dependence of the Hall angle and the diamagnetic susceptibility in order to develop a framework to quantify the disorder parameters, namely disorder potential V0 and the characteristic lengths ξ, as a function of silver deficiency. These quantities will be compared as silver deficiency is varied. We will discuss the implication of our results in terms of generalized conditions for emergence of linear magnetoresistance. |
Thursday, March 5, 2020 12:39PM - 12:51PM |
S27.00008: Quantum Transport in Epitaxial Ultra Wide Bandgap Aluminum Gallium Oxide Tunnel Heterostructures Nicholas Tanen, Celesta Chang, Vladimir Protasenko, Jonathan McCandless, David Anthony Muller, Huili Xing, Debdeep Jena In this work, we studied the epitaxial growth of the wide-band gap, monoclinic beta-Ga2O3 (~4.4-4.9 eV) and (AlxGa1-x)2O3 (~4.4-9.0 eV, Al% = 0-100) using molecular beam epitaxy on (010) beta-Ga2O3 substrates. We will discuss the optimum growth conditions for both materials and how the formation of Ga interstitial-divacancy complexes in unoptimized growths of (AlxGa1-x)2O3 can lead to the formation of unwanted phases of Ga2O3 in our heterostructures. Additionally, tunnel barrier structures made with an (AlxGa1-x)2O3 layer sandwiched between two n+ Ga2O3 layer are studied to explore tunneling behavior in this material system. The current-voltage characteristics are measured for a varying Al composition and the (AlxGa1-x)2O3 barrier thickness. Using the Wentzel–Kramers–Brillouin approximation and Non-equilibrium Green’s Function formalism, the current-voltage characteristics of these tunnel barrier devices are simulated and compared to experimental data. The above study helps identify the conduction band offset ΔEc a critical unknown in this material family directly from transport. The ΔEc thus found between beta-(AlxGa1-x)2O3 and beta-Ga2O3 is compared to those extracted from XPS, capacitance-voltage measurements, and also by DFT. |
Thursday, March 5, 2020 12:51PM - 1:03PM |
S27.00009: Lateral charge carrier transport properties of B-10 enriched hexagonal boron nitride epilayers Samuel Grenadier, Avisek Maity, Jing Li, Jingyu Lin, Hongxing Jiang Hexagonal boron nitride (h-BN) has emerged as a promising candidate for many technologically significant applications due to its unique physical properties. However, h-BN is one of the least studied members of the III-nitride materials system and many important fundamental properties including room temperature carrier mobility, lifetime and surface recombination velocity remain unexplored. We report Time-of-Flight (TOF) probed room temperature lateral carrier drift mobilities (µ) and lifetimes (τ) for both electrons and holes in highly resistive, wide bandgap h-BN epilayers. Photoconductive type detectors were fabricated from freestanding B-10 enriched h-BN material. We obtained values of µe ~ 34 cm2/Vs for electrons and µh ~ 36 cm2/Vs for holes and carrier lifetimes on the order of 10 μs. Surface recombination velocity (S) was then calculated by combining the µ from TOF with the ratio of S to µ (S/µ) extracted directly from the bias voltage dependence of photocurrent. These results represent a valuable contribution to the understanding of the electrical transport properties of h-BN. |
Thursday, March 5, 2020 1:03PM - 1:15PM |
S27.00010: Physical properties at the 157K-phase transition in Pr4Ni3O10 Shangxiong Huangfu, Dariusz Gawryluk, Xiaofu Zhang, Ekaterina Pomjakushina, Andreas J Schilling As a member of the the Ruddlesden–Popper Ln4Ni3O10 series rare earth nickelates, the Pr4Ni3O10 is constituted by three Ni-O layers piled up to a quasi-two-dimensional perovskite-like structure[i], and shows mixed Ni valent states of +2 and +3. A phase transition at ~ 157 K has already been observed in previous studies, which was interpreted as a charge-density wave (CDW) transition[ii],[iii]. We have grown single crystals of Pr4Ni3O10 in high oxygen pressure, and report on the physical properties around that phase transition, such as heat capacity, magnetization and electron transport. We observe a distinct anisotropy between in-plane and out-of-plane properties both in zero-field and in magneto-resistance. In addition, the magnetic susceptibility obeys a Curie-weiss law, with different Curie constants for the high temperature and the low temperature phases. We discuss a possible scenario in which a change of the d orbitals of the Ni ions at the Fermi level explains the changes in all these measured quantities at the phase transition. |
Thursday, March 5, 2020 1:15PM - 1:27PM |
S27.00011: Charge transport mechanism near crystal edge of layered halide perovskites Xiujun Lian, Enzheng Shi, Letian Dou, Hanwei Gao Halide perovskites show superior optical and electrical properties, which make this group of materials promising for highly efficient optoelectronic applications. Researchers have reported that there existed below-bandgap energy states at the edges of the layered perovskites and the presence of these lower energy states resulted in highly improved solar cell efficiency. In our work, the photophysics investigation near crystal edge unveiled the local charge transport mechanism and energy flow in layered halide perovskites, which will provide vital guidance for designing and engineering highly efficient optoelectronics based on this group of materials. |
Thursday, March 5, 2020 1:27PM - 1:39PM |
S27.00012: Dynamic disorder in BaTiS3 Raphael Hermann, Michael E Manley, Barry Winn, Katharine L. Page, Ahmet Alatas, Jaeyun Moon, Austin Minnich, Jayakanth Ravichandran BaTiS3 exhibits a hexagonal perovskite structure comprised of columns of sulphur coordinated Ti linked by barium making it a quasi-1D structure. Neutron pair distribution function measurements reveal that the Ti atomic displacement parameters increase with decreasing temperature. This observation suggest proximity to a ferroelectric type phase transition or, alternatively, dynamic disorder persisting in the ground state. A combination of phonon spectroscopy by inelastic x-ray scattering and inelastic neutron scattering supports the dynamic disorder scenario which extends into the quantum regime with Ti occupying a double-well potential. This unique dynamics have a profound consequence on the thermal conductivity and suggest a novel mechanism for thermal transport design. |
Thursday, March 5, 2020 1:39PM - 1:51PM |
S27.00013: A High Throughput DFT Study of Half Heusler Solid Solution Mixtures Andrew Lee, Shashwat Anand, Logan Ward, Christopher Mark Wolverton Half heuslers exhibit properties well-suited for thermoelectrics. The best performing half heusler thermoelectrics such as TiNiSn, NbFeSb, and ZrCoBi-based systems are solid-solution alloys with disorder scattering which reduces thermal conductivity. However, only a handful of such alloy systems have been reported. Furthermore, these systems are studied with mixing on just one of the three sub-lattices at a time. Hence, a comprehensive study of solubility in mixed alloy systems can guide future choices of half heusler thermoelectrics. Here, we use DFT to calculate mixing energies and relative stabilities of around 1000 binary solid solutions using restrictions of isovalent substitution and single sublattice mixing. Half of these have mixing energies suitable for forming single phase alloys, when |E_mix| < 0.05 eV/atom (kBT @ 600K). We then extend our search to higher component mixtures and the unexplored concept of multi-sublattice mixing. Continuing with DFT is too slow given the combinatorically expanding composition space, so we develop a machine learning model to help classify mixing behavior. With trends identified from the model and DFT, we hope to better guide future experiments toward improved half heusler thermoelectrics. |
Thursday, March 5, 2020 1:51PM - 2:03PM |
S27.00014: Low temperature thermopower in CoSbS Qianheng Du, Milinda Abeykoon, Yu Liu, Gabriel Kotliar, Cedomir Petrovic Thermopower of FeSb2 reaches colossal values of up to -45 mV/K, however, the physical mechanism is not well understood. In order to make progress and enable predictive materials design, it is important to discover new materials with high thermoelectric parameters and with tunable physical properties. Recently, it was shown that CoSbS could be a high-temperature thermoelectric material due to several positive factors that work simultaneously to enhance its thermoelectric performance. We report giant thermopower S = 2.5 mV/K in CoSbS single crystals [1], a material that shows strong high-temperature thermoelectric performance when doped with Ni or Se. Changes of low temperature thermopower induced by magnetic field point to mechanism of electronic diffusion of carriers in the heavy valence band. Intrinsic magnetic susceptibility is consistent with the Kondo-Insulator-like accumulation of electronic states around the gap edges. This suggests that giant thermopower stems from temperature-dependent renormalization of the noninteracting bands and buildup of the electronic correlations on cooling. |
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S27.00015: Large magnetothermopower and anomalous Nernst effect in HfTe5 Junfeng Hu, Marco Caputo, Eduardo Bonini Guedes, Sa Tu, Edoardo Martino, Arnaud Magrez, helmuth berger, J. Hugo Dil, Haiming Yu, Jean-Philippe Ansermet Topological quantum materials have stimulated a growing attention because they reveal novel aspects of condensed matter physics and point to new opportunities in materials science, in particular for thermoelectrics. Here, we experimentally study thermoelectric effects in HfTe5, which was predicted to be at the boundary between strong and weak topological insulators. The magnetic field dependence of HfTe5 thermoelectric properties attests to the anomalous character of this material, supported by our angle-resolved photoemission spectroscopy (ARPES) measurements. A possible topologically non-trivial band structure is proposed to account for our observations. Our results constitute a highly constraining set of data for any model of transport based on HfTe5 band structure. Furthermore, the extraordinary thermoelectric properties suggest a new paradigm for the development of thermoelectric applications based on layered transition-metal chalcogenides. |
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