Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B66: Artificially Structured Materials and InterfacesRecordings Available
|
Hide Abstracts |
Sponsoring Units: DCMP Chair: Eric Stinaff, Ohio Univ Room: Hyatt Regency Hotel -Grant Park D |
Monday, March 14, 2022 11:30AM - 11:42AM |
B66.00001: Ultrafast generation and detection of propagating coherent acoustic phonon wave packets in ultra-thin iron pnictide films Di Cheng We observe pronounced oscillations in differential reflectivity of 9 nm and 60 nm BaFe2As2 (Ba-122) thin films using ultrafast optical spectroscopy. Our studies show that the oscillations result from propagating longitudinal acoustic (LA) phonon wave packets with strong thickness and temperature dependence. Particularly, the experimentally measured oscillation frequency approaches to 50 GHz for the ultra-thin film. Our calculations show that Young's modulus of 9 nm thin film is nearly four times as large as that of 60 nm thin film, consistent with the experiment. The increase in Young's modulus as thickness decrease was attributed to the decrease in parent Ba-122 tetragonality c/a near the film-substrate interface due to material-substrate mismatch effect. The temperature-dependent change in LA phonon frequency was attributed to the change in parent Ba-122 othorhombicity (a-b)/(a+b). |
Monday, March 14, 2022 11:42AM - 11:54AM |
B66.00002: Mid-Infrared Intersubband Absorption in Strain-Balanced Non-Polar (In)AlGaN/InGaN Multi-Quantum Wells Trang Nguyen, Oana Malis, Michael J Manfra, Brandon Dzuba, Yang Cao, Alexander Senichev, Rosa Diaz Strain-balanced non-polar m-plane (In)AlGaN/InGaN quantum wells are shown for the first time to exhibit mid-infrared intersubband absorption in the 3.4-5.1m range. A series of samples was grown using plasma assisted molecular beam epitaxy as an alternative to high Al-composition non-polar m-plane AlGaN/GaN quantum wells. The structural properties of the samples were determined using high resolution x-ray diffraction and transmission electron microanalysis. The experimental intersubband transition energy of each sample was measured using direct and attenuated total reflection Fourier transform infrared spectroscopy and compared to energies calculated using local-density and Hartree-Fock approximations. The effect of different material parameters such as quantum well width, barrier alloy, and charge density on the transition energy is explored to determine the potential of this material for practical applications. |
Monday, March 14, 2022 11:54AM - 12:06PM |
B66.00003: Coexisting Polar and Antipolar BiFeO3 Phases Imaged by Microwave Microscopy Jia Yu, Lucas Caratta, Piush Behera, Daehun Lee, Ramamoorthy Ramesh, Keji Lai The dielectric response of ferroelectrics plays an important role in their potential applications. As a model material system, the BiFeO3-TbScO3 (BFO-TSO) superlattices may exhibit coexistence of centrosymmetric (antipolar) and non-centrosymmetric (polar) phases in the BFO layers. Using microwave impedance microscopy (MIM), we quantitatively measured the permittivity and conductivity contrast between the antipolar and polar phases at GHz frequencies. Interestingly, while the antipolar phase remains highly insulating, the polar phase with two orientations of the net polarization displays the semiconducting behavior with a resistivity five orders of magnitude lower than that of the bulk BFO. Moreover, the application of in-plane electric fields can lead to reversible and nonvolatile interconversion between the two phases, which is also imaged by the MIM. Our work shows a unique method to spatially resolve the dielectric and conduction properties in complex ferroelectric structures, which may extend to other materials as well. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B66.00004: Ghost-induced exact degeneracies Emroz Khan, Sanjay Debnath, Evgenii Narimanov We show that the recently discovered "ghost coupling" (Opt. Lett. 46, 1708-1711 (2021)) – a new type of mode interaction mediated by a special class of nonuniform waves in biaxial anisotropic media – can lead to exact frequency degeneracies in guided modes. In addition to explaining the mode interaction through a coupled mode analysis, we also show that the interaction can lead to emergence of exceptional points which can offer a new approach to optical sensing with better performance. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B66.00005: The effect of nanocrystal shape and superlattice morphology on superfluorescence in semiconductor nanocrystal superlattices Sushrut Ghonge, David Engel, Francesco Mattiotti, Giuseppe Luca Celardo, Masaru K Kuno, Boldizsar Janko Cooperative emission of radiation from multiple emitters (superfluorescence or SF) has been predicted and even observed in molecular aggregates. In superlattices of semiconductor nanocrystals, theory predicts that SF enhancement of up to N (the number of nanocrystals) can be observed. However, only weak (~6 orders of magnitude less than N) superfluorescence has been observed in such systems. It has been proposed that this is because the SF is sensitive to thermal decoherence (finite temperature) and variations in the sizes of nanocrystals. In this talk, we show how modifying the shape of the nanocrystals and the morphology of the superlattice makes SF more robust to temperature and nanocrystal size variations. We will show that superfluorescence from cuboid-shaped nanocrystals and 2D superlattices is more robust than cubic nanocrystals and 3D superlattices. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B66.00006: Atomic-level Interfacial Broadening in Ultra-Short Superlattices Anis Attiaoui, Gabriel Fettu, Samik Mukherjee, Matthias Bauer, Oussama Moutanabbir Artificially fabricated superlattices (SL) offers the possibility to render optically inactive materials into strong light emitters and absorbers by melding two indirect-gap materials into one strongly dipole-allowed direct-gap material. The artificial periodicity in these low-dimensional systems provides an additional degree of freedom to engineer their band structure and thus improve their electronic and optical properties. Using SiGe/Si SLs as a model system, recent experiments indicated that the interfacial abruptness and uniformity are of key importance to control the electronic and optical properties. Herein, based on a recent method to map in 3-D the roughness and uniformity of buried epitaxial interfaces in Si/SiGe SLs with a layer thickness in the 1.5-7.5 nm range [1], we address the optical properties of these SLs using room temperature spectroscopic ellipsometry. Our systematic studies revealed a new SL-related optical transition between 2.1 and 2.9 eV. A theoretical framework has been developed based on the 14-band k·p formalism, where the interfacial roughness specificities were included, to explain the origin of the transition. Additionally, the k·p Hamiltonian was modified to consider the effect of microscopic interface asymmetry (MIA). To validate the developed framework, experimental optical characterization of four different Sim/(Si1-xGex)m SLs (the mean Ge concentration of the Si1-xGex layers within the SLs is in the ~25 to ~30 at. % range and m is the periodicity of the SLs) will be presented and discussed. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B66.00007: Analysis of M-Superlattice structures for infrared photodetection Anuja Singh, Swarnadip Mukherjee, Bhaskaran Muralidharan Type-II Superlattices (T2SL) comprising of InAs/(In,Ga)Sb are currently leading candidates for infrared photodetection. In order to advance the device design, we perform a thorough investigation on the band properties of M-Superlattice (MSL) structures as well as the microscopic properties using the Keldysh non-equilibrium Green's function (NEGF) technique. Using the 8-band k.p method with the envelope function approximation which includes the microscopic interface asymmetry (MIA) and strain effects, we demonstrate the effects of AlSb width on the band edge variations and density-of-states (DOS) effective masses for varied constituent material widths covering the MWIR-LWIR range. Delving into the microscopic properties such as the miniband formation and transmission properties, we depict the advantage of using MSL over T2SL as an absorber as it provides larger interband overlap at the interface for better optical properties. Further comparisons on these structures are made by inspecting in detail the dark current tunneling transport with the inclusion of scattering processes via the momentum dephasing model within the NEGF technique. Furthermore, with the help of local density of states obtained from NEGF, we introduce two MSL configurations that provide reasonable conduction band and valence offsets for a particular T2SL absorber configuration. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B66.00008: First-principles studies on the interfacial conducting states on the zincblende semiconductor superlattices Byeol Kang, Joo-Hyoung Lee Two-dimensional (2D) conducting states on the interface between insulating materials have brought about enormous interests because they show a variety of fascinating physics such as high-mobility and superconductivity. Since the discovery of 2D interfacial conducting states at SrTiO3-based heterointerfaces, it has been reported that 2D interfacial metallicity is also observed in certain zincblende semiconductor superlattices. To explore wider materials classes, we investigate the interfacial characteristics on the zincblende semiconductor superlattices composed of III-V(AlAs, AlP, GaAs, GaP)/Si, II-VI(ZnS, ZnSe)/Si and III-V/II-VI. Our electronic structure calculations demonstrate that the formation of the interfacial conducting states in zincblende semiconductors is very general and their existence highly depends on the orientation and superlattice period. To clarify the origin of the conducting states, we analyze the charge transfer at each orientation of the interfaces. It is found that the charge transfer is governed by the compositions of the interfacial atoms on each superlattice and that the difference in electronegativity between interfacial atoms plays a crucial role in forming the conducting states. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B66.00009: The giant negative magnetoresistance in two-dimensional electron gases Thomas Heinzel, Beate Horn-Cosfeld, Jakob Schluck The giant negative magnetoresistance (GNMR), observed in two-dimensional electron gases of high mobility, is studied by controlled definition of additional short range scatterers in form of two-dimensional Lorentz arrays of varying obstacle density, as well as in the presence of edge scattering. The results support models which ascribe the temperature-independent regime of the GNMR to strong, classical scattering and the temperature-dependent regime to electron-electron interactions under the influence of mixed disorder. The threshold magnetic field, which separates the two regimes, is in rough agreement with the lower percolation transition of the Lorentz array. At large obstacle densities, interaction corrections are suppressed and memory effects like retroreflection and skipping-orbit transport become more relevant. Shape, amplitude and width of the GNMR depend sensitively on the time scales of the contributing scattering mechanisms, which comprise short- and long-range scattering at defects as well as scattering at the sample edges and at phonons. This interplay can lead to qualitatively similar shapes for quite different parameter values. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B66.00010: Breakdown of Universal Scaling for Nanometer-Sized Bubbles in Graphene Renan Villarreal, Zviadi Zarkua, Pin-Cheng Lin, Fahim Faraji, Nasim Hassani, Harsh Bana, Maya Narayanan Nair, Hung-Chieh Tsai, Manuel Auge, Felix Junge, Hans Hofsass, Stefan De Gendt, Steven De Feyter, Steven Brems, Harriet Ahlgren, Erik C Neyts, Lucian Covaci, Francois M Peeters, Mehdi Neek-Amal, Lino M.C. Pereira Owing to its unrivalled elasticity and strength, graphene is able to hold matter at extreme pressures in the form of bubbles with dimensions down to the nanometer scale [1,2]. These bubbles offer new opportunities to explore physics and chemistry and under the extreme conditions that both graphene and the trapped matter are subject to. While previous research has mostly dealt with bubbles with a radius of few nm and larger, the sub-nanometer regime remains largely unexplored. Here, we report the formation of graphene nanobubbles with radius of the order of 1 nm, which are produced using ultralow energy implantation of noble gas ions (He, Ne and Ar) into graphene grown on a Pt (111) surface [3]. We show that the universal scaling of the aspect ratio (height over radius), which has previously been established for larger bubbles (with radius of few nm and higher) [1], breaks down when the bubble radius approaches 1 nm , as the bubble height converges to a minimum value corresponding to one atomic monolayer [3]. Moreover, we observe that the bubble stability and aspect ratio depend on the substrate onto which the graphene is grown and on trapped element [3]. We discuss these dependencies in terms of the role of the atomic compressibility of the noble gases as well as of the adhesion energies between the three constituents: graphene, substrate and noble gas atoms. The high strain (of the order of 10%) induced in graphene by the trapped atoms and the high van der Waals pressure (of the order of tens of GPa) inside the bubbles illustrate the unique characteristics of this sub-nanometer bubble regime, compared to the previously studied (larger) nanobubbles. We also discuss prospects to explore our approach (based on ultralow energy ion implantation) in the context of inducing periodic pseudomagnetic fields and flat bands in graphene. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B66.00011: Tuning coherent-phonon heat transport in oxide superlattices. Francisco Rivadulla, David Bugallo, Eric Langenberg, Noa Varela-Dominguez, Enrique Carbo-Argibay, Adolfo Otero-Fumega, Victor Pardo, Irene Lucas, Luis Morellon, Araceli Gutierrez-Llorente Accessing the regime of coherent phonon propagation in nanostructures opens new possibilities to control the thermal conductivity in energy harvesting devices, phononic circuits, etc. Here we discuss the contribution of coherent phonons to the thermal conductivity of LaCoO3/SrTiO3 and PbTiO3/SrTiO3 superlattices, from 25K to 300 K, and over a wide range of periods and thicknesses. We demonstrate that the contribution of coherent phonons to these superlattices is relevant in the whole period length and can be substantially reduced by small variations of the periodicity. Actually, by using slightly aperiodic strucures, we have being able to reduce the thermal conductivity of the superlattices by 20%, at room temperature. This may have an interesting application in the development of low thermal conductivity devices, in which maintaining a relatively large thickness and clean interfaces is important for not deteriorating electrical transport, as in thermoelectrics. We also discuss the role of interface mixing and epitaxial relaxation as an extrinsic, material dependent key parameter for understanding the thermal conductivity of oxide superlattices, as well as the effect of cooperative ferroelectric domains in PbTiO3/SrTiO3 superlattices. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700