Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y6: Optical and Electrical Properties of Hybrid Nanostructures |
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Sponsoring Units: DCMP DMP Chair: Peter Brereton, United States Naval Academy Room: 006A |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y6.00001: Tuning the charge transfer plasmon in a metallic nanoparticle dimer bridged by a quantum dot Vikram Kulkarni, Alejandro Manjavacas, Peter Nordlander Localized surface plasmon resonances (LSPR) are a subject of intense experimental and theoretical research interest. LSPR have found applications in catalysis, solar energy, cancer therapy, and surface enhanced Raman spectroscopy (SERS). This is due to the exceptional light capturing and focusing capabilities of plasmonic nanostructures. An LSPR of particular interest is the charge transfer plasmon (CTP). This mode may be excited when two plasmonic nanoparticles are bridged by a conductive junction. The CTP is extraordinarily sensitive to the conductive properties of the junction. Here we perform a theoretical investigation of the CTP when two plasmonic nanoparticles are bridged by a quantum dot. All simulations are done using the time dependent density functional theory (TDDFT). By modulating the electronic structure of the quantum dot we are able to effectively turn the CTP on and off. Specifically, the CTP emerges only when a quantum dot energy level is resonant with the fermi energy of the plasmonic nanoparticles. We verify that the conductance through the junction is on the order of the quantum unit of conductance. This work is of great interest to the future design of plasmonic and molecular electronic systems. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y6.00002: Highly tunable gold nanorod dimer resonances mediated through conductive junctions Jake Fontana, Banahalli Ratna Tailoring the resonant frequency in plasmonic nanostructures is critical to developing disruptive metamaterial technologies. Here we numerically study the optical properties of gold nanorod dimers connected end-to-end by a thin metallic bridge [1]. We find the resonant frequency along the long axis of the dimer shifts linearly with the nanorod aspect ratio behaving as it was a single nanorod with an aspect ratio nearly an order of magnitude larger. We show by controlling the material and geometry of the connecting bridge the effective depolarization factor of the dimer is significantly modulated tuning the resonant frequency over a decade, from 1 to 10 $\mu$m. We present an alternative description for the emergence and behavior of the dimer resonance using a straightforward ``Drude-like'' model and self-assembly experiments creating such structures. \\[4pt] [1] J. Fontana and B. R. Ratna, Applied Physics Letters \textbf{105} (2014). [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y6.00003: Surface Plasmon Resonance enhancement via oblique thin film deposition on gratings Zhaozhu Li, Michael Klopf, George Schwartz, Matthew Heimburger, Lei Wang, Kaida Yang, Rosa Lukaszew Surface plasmon resonance (SPR) occurs when light shines at a dielectric-metallic interface under certain configurations such that an evanescent polariton can be excited. This surface plasmon polariton travels across the interface exhibiting electric field intensity greatly enhanced with respect to the incident light, evidenced by the observation of a deep angular reflectivity scans at the resonance angle. To excite the SPR, one can use a diffraction grating coupler in order to satisfy the dispersion relationship, noting that within certain grating-groove aspect-ratio, the electric field intensity in the surface polariton can be further enhanced by increasing the grating amplitude. We have applied oblique shadow deposition (OSD) to deposit metallic layers onto gratings to enhance their grating amplitudes and compare them to films deposited at normal incidence. We report on the effects on the SPR of such configurations, by comparing the results of OSD samples with those for normal incident deposited samples. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 8:48AM |
Y6.00004: Plasmon Excitations for a Linear Assembly of Metallic Spheres Bo Gao, Liubov Zhemchuzhna, Andrii Iurov, Godfrey Gumbs, Danhong Huang We present a general formalism for calculating the Coulomb excitations of a linear array of interacting electron gases confined to the outside surfaces of three spherical shells. The response of these incompressible 2D electron gases to an external electromagnetic field results in charge density oscillations whose anisotropy with respect to the axis of quantization will be discussed. The dependence of the frequency of the plasma oscillations on the radius of the spheres as well as their separation has been a subject of our investigation and detailed results will be presented. We provided complete numerical results for the plasmon excitation of such system and concluded that the plasmon demonstrate quite different behavior from the earlier considered case of a S2DEG triad - they are not symmetric on the sign of each potential element for z-alignment and the interaction of the two far-removed spheres is no longer negligible. [Preview Abstract] |
Friday, March 6, 2015 8:48AM - 9:00AM |
Y6.00005: Aperiodic Aharonov-Bohm oscillations in coherent transport through a periodic array of quantum dots L.S. Petrosyan, T.V. Shahbazyan We study resonant tunneling through a periodic square array of quantum dots sandwiched between modulation-doped quantum wells. If a magnetic field is applied parallel to the quantum dot plane, the tunneling current exhibits a highly complex Aharonov-Bohm oscillation pattern due to interference of multiple pathways traversed by a tunneling electron. Individual pathways associated with conductance beats can be enumerated by sweeping the magnetic field at various tilt angles. Remarkably, Aharonov-Bohm oscillations are aperiodic unless the magnetic field slope relative to quantum dot lattice axes is a rational number. [Preview Abstract] |
Friday, March 6, 2015 9:00AM - 9:12AM |
Y6.00006: Hyperbolic polaritons in nanoparticles Zhiyuan Sun, Angel Rubio, Francisco Guinea, Dimitri Basov, Michael Fogler Hyperbolic optical materials (HM) are characterized by permittivity tensor that has both positive and negative principal values. Collective electromagnetic modes (polaritons) of HM have novel properties promising for various applications including subdiffractional imaging and on-chip optical communication. Hyperbolic response is actively investigated in the context of metamaterials, anisotropic polar insulators, and layered superconductors. We study polaritons in spheroidal HM nanoparticles using Hamiltonian optics. The field equations are mapped to classical dynamics of fictitious particles (wave packets) of an indefinite Hamiltonian. This dynamics is quantized using the Einstein-Brillouin-Keller quantization rule. The eigenmodes are classified as either bulk or surface according to whether their transverse momenta are real or imaginary. To model how such hyperbolic polaritons can be probed by near-field experiments, we compute the field distribution induced inside and outside the spheroid by an external point dipole. At certain magic frequencies the field shows striking geometric patterns whose origin is traced to the classical periodic orbits. The theory is applied to natural hyperbolic materials hexagonal boron nitride and superconducting LaSrCuO. [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y6.00007: Generation of acoustic terahertz waves in hybrid InGaN/GaN quantum wells Meg Mahat, Antonia Llopis, Tae Youl Choi, Sergio Periera, Ian Watson, Arup Neogi We have carried out differential transmission measurements on InGaN/ GaN quantum wells with Au nanoparticles inserted inside V-pits with high filling fraction. We have observed acoustic wave packets generated with multiple THz frequencies as 0.12 THz from GaN buffer layer, 0.22 THz from Au-InGaN multiple quantum wells region, 0.07 THz from sapphire substrate, and 0.17 THz mixed signals from the sample. These THz wave packets are observed as a result of generation of coherent acoustic phonons propagating in hybrid Au-InGaN quantum wells. The study of these acoustic THz wave generation is crucial for the imaging of nanostructures. [Preview Abstract] |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y6.00008: Magnetic field- and frequency-dependence- of the phase-shift in the linearly-polarized microwave radiation-induced magnetoresistance oscillations in the GaAs/AlGaAs system Han-Chun Liu, Tianyu Ye, Werner Wegscheider, Ramesh Mani Nonequilibrium transport studies of the radiation-induced magnetoresistance oscillations (RIMOs) have revealed striking photo-excited zero-resistance states in the GaAs/AlGaAs two-dimensional electron system [1]. Further observations show that RIMOs are linear-polarization-angle-sensitive and follow a sinusoidal fitting formula, R$_{\mathrm{xx}}(\theta )=$A $\pm$ Ccos$^{2}(\theta $-$\theta_{0})$ where R$_{\mathrm{xx}}$ is the diagonal resistance, $\theta $ is the polarization angle, and $\theta_{0}$ is the extracted phase shift. At the present, $\theta_{0}$ is known to be magnetic- and frequency dependent [2]. Here, we perform magnetic mappings at small $\theta $ intervals, at a number of radiation frequencies, to study the variation of the phase shift with the magnetic field and frequency. The relationship between phase shift and magnetic fields/frequency will be critically examined and reported in this presentation. \\[4pt] [1] R. G. Mani \textit{et al.}, Phys. Rev. B 84, 085308 (2011). \\[0pt] [2] A. N. Ramanayaka \textit{et al.}, Phys. Rev. B 85, 205315 (2012). [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y6.00009: Electrochemically grown InSb nanowires: challenges and growth determined properties Abhay Singh, Usha Philipose InSb nanowires have myriads of applications such as electronic, optoelectronic, and magneto resistive devices. Synthesis of InSb nanowires in the pores of anodic alumina oxide (AAO) template by direct current electrodeposition is challenging because it involves several steps including opening of barrier layer at the bottom of AAO pores, dissolving of the AAO template post-nanowire growth, followed by extraction of InSb nanowires from solution. We will present evidence of these challenges. The InSb nanowires had good composition and crystalline quality as will be shown by EDX, X-ray, and Raman spectroscopy. Transport measurements made on a single InSb nanowire and on an array of nanowires will be presented. A single nanowire connected in an FET type configuration was used to determine carrier concentration and mobility. By tuning the growth parameters during electrochemical deposition, it is possible to modulate the nanowire composition. Temperature dependent measurements are used to show the semiconducting behavior of the nanowires. [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y6.00010: Superlattice Phenomena in Nanohelices Charles Downing, Matthew Robinson, Mikhail Portnoi Recently artificially-created nanohelices have been demonstrated in various semiconductor systems. We argue that subjecting a nanohelix to an electric field normal to its axis turns it into a superlattice with easily-tunable electronic properties. We investigate such a system, also subjected to a longitudinal electric field along the nanotube axis, and find Bloch oscillations and negative differential conductivity. Taking into account Zener tunneling across the band gap, we find the characteristic N-type dependence of electron drift velocity on the longitudinal field which is commonly used in high-frequency electronics. The merits of using a nanohelix for novel tunable device applications are assessed. We also study dipole transitions across the energy gap, which can be tuned to the THz range by experimentally attainable external fields. There is a drastic change in selection rules for a helix in a transverse field compared to the case of purely chiral structures. For the excitation propagating along the nanohelix axis our results are somewhat similar to those found for a quantum ring pierced by a magnetic flux, with the momentum of a quasiparticle in a helix playing the same role as a flux through a ring. We also discuss possible devices which could utilize these phenomena. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y6.00011: Tunable Quantum Temperature Oscillations in Graphene Nanostructures Justin Bergfield, Mark Ratner, Charles Stafford, Massimiliano Di Ventra Thermal scanning probe microscopy techniques are now capable of nanometer spatial resolution and millikelvin temperature accuracy, raising the fundamental question: What is the meaning of temperature for a quantum system operating far from equilibrium? We investigate this question theoretically using a realistic model\footnote{J.P. Bergfield, S.M. Story, R.C. Stafford, C.A. Stafford, ACS Nano 7, 4429-4440 (2013)} of a scanning thermal microscope with atomic resolution, operating in the tunneling regime in ultrahigh vacuum. The thermometer acts as an open third terminal in a thermoelectric circuit. We investigate the temperature distributions in molecular junctions and graphene nanoribbons\footnote{J.P. Bergfield, M.A. Ratner, C.A. Stafford, M. Di Ventra, arXiv:1305.6602.} under thermal bias, and find that the local temperature in these systems exhibits quantum oscillations; quantum interference mimics the actions of a Maxwell Demon, allowing electrons from the hot electrode to tunnel onto the temperature probe when it is at certain locations near the system, and blocking electrons from the cold electrode, or vice versa. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y6.00012: Mechanism and Limitation of Heat Conduction in Three-Phase Polymer Composites Having Carbon Nanotubes and Inorganic Nanoparticles Hai Duong, Feng Gong, Dimitrios Papavassiliou For the first time, an Off-Lattice Monte Carlo method is developed successfully to predict thermal conductivities ($K_{\mathrm{eff}})$ of three-phase composites having carbon nanotubes (CNTs) and tungsten disulfide (WS$_{2})$ nanoparticles more accurately and faster than previous methods such as effective medium theories, molecular dynamics and finite element methods. The $K_{\mathrm{eff}}$ predicted by our model using a random walk algorithm and taking into account various thermal boundary resistances at each interface and inter-CNT contact has an excellent agreement with experimental data. Our model can comprehensively explain the mechanism of heat conduction in complex composite structures. Effects of WS$_{2}$ and CNT morphologies (diameter, length, inter-contact, bundle), CNT concentrations, CNT orientations (parallel, random and perpendicular to heat flux) and thermal boundary resistances of CNT-polymer, WS$_{2}$-polymer, CNT-CNT, CNT-WS$_{2}$ on heat conduction limitation of the three-phase composites are also investigated systematically. Our model can be also applied to the biological and nanofluid systems. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y6.00013: One or two dimensional electronic states in gold nanowires on germanium? Nick de Jong, Emmanouil Frantzeskakis, Ren\'e Heimbuch, Andrei Varkhalov, Harold Zandvliet, Mark Golden Inspired by the formulation of Tomonaga-luttinger liquid (TLL) theory in the 1960's and its prediction of a spectacular breakdown of Fermi liquid theory in 1D, people have been searching for one dimensional electronic systems. With experimental developments like the advent of scanning tunneling microscopy (STM) and the manipulation of matter on the nanometer and sub nanometer scale, this field has become increasingly accessible for the experimentalist. Self-organised metallic chains on semiconductor surfaces are a class of systems which could harbor 1D behavior. In this field, Au nanowires on the Ge(100) surface have been the subject of debate, with reports of 1D bands from both ARPES and STM (1) and 2D bands in the same system displaying no Luttinger like behavior (2). Here we present high resolution ARPES data from both the Au/Ge(100) system and a new nanowire system: Au/Ge(110). By comparing these different systems with each other an with the electronic structure of the bare Ge(110) surface, we try to give a definitive answer on the question of the dimensionality of the electronic structure of Au nanowires on germanium. \\[4pt] [1] J. Schafer et al., PRL101, 236802 (2008)\\[0pt] [2] K. Nakatsuji, at al., PRB80, 081406(R) (2009) [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y6.00014: Observation of Franck-Condon Blockade in Single Molecules Gated by Local Electric Field Aidi Zhao, Chunsheng Zhou, Weiyi Wang, Guangjun Tian, Huan Shan, Shulai Lei, Yingbo Zhao, Yi Luo, Qunxiang Li, Bing Wang, J.G. Hou Electron transport through single molecules is greatly influenced by a discrete spectrum of vibrational modes in strong electron-vibron coupling regime. Theory predicts a current suppression at low biases known as Franck-Condon blockade. However, how Franck-Condon blockade emerges in in a real orbital-gated single molecule transistor is still elusive. In this study, by using a low-temperature scanning tunneling microscope, we report the real-space observation of Franck-Condon blockade in single molecules adsorbed on metal surfaces. The frontier molecular orbitals and charge state of the molecules are shown to be electrostatically gated by variation in the underlying surface potential and local chemical environment, allowing the observation of coulomb blockade as well as the Franck-Condon blockade. Moreover, strongly enhanced inelastic cotunneling is evidenced to dominate the electron transport in the Franck-Condon blockade regime, leading to unprecedented high-contrast single molecule vibrational spectroscopy and microscopy. [Preview Abstract] |
Friday, March 6, 2015 10:48AM - 11:00AM |
Y6.00015: Two-channel Kondo effect and the low-temperature crossover Andrew Keller, Lucas Peeters, Ireneusz Weymann, C\u{a}t\u{a}lin Pa\c{s}cu Moca, Diana Mahalu, Vladimir Umansky, Gergely Zar\'and, David Goldhaber-Gordon The two-channel Kondo (2CK) state, where a spin-1/2 impurity is equally exchange-coupled to two independent reservoirs, is a canonical non-Fermi liquid state. Experimental observations are rare because of its sensitivity to common and hard-to-control perturbations. We implement experimentally a 2CK state in a coupled dot-grain system (Potok, et al., doi:10.1038/nature05556), and explore the physics of the low-temperature crossover: how magnetic field and gate voltage drive the system towards a Fermi liquid ground state. Our experimental findings are corroborated by detailed numerical renormalization group modeling of our device. [Preview Abstract] |
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