Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session A24: Electronic Transport through Individual NanostructuresFocus
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Sponsoring Units: DMP Chair: Pierre Darancet, Argonne National Laboratory Room: 323 |
Monday, March 14, 2016 8:00AM - 8:12AM |
A24.00001: Quantum Transport and Emergence of Superradiant States Amin Tayebi, Vladimir Zelevinsky Quantum transport is investigated in the framework of the Feshbach projection formalism. This approach provides an alternative to popular methods such as the Feynman diagrammatic techniques and the master equation. The suggested method, being practically simpler, is quite general, not perturbative and reveals new physics, including the sharp redistribution of decay widths and the emergence of short-lived ``superradiant" states and long-lived ``trapped" states for sufficiently strong coupling to the leads. The superradiant states significantly enhance the transport phenomenon. An additional advantage of the formalism is its flexibility, which allows for a straightforward incorporation of disorder and additional degrees of freedom, such as phonons. Numerical results of transport through specific structures is presented. The interplay of superradiance and polaronic self-localization effects is discussed. [Preview Abstract] |
Monday, March 14, 2016 8:12AM - 8:24AM |
A24.00002: Validity criteria for scattering rates obtained with Fermi's golden rule in semi-classical transport Kristof Moors, Bart Sorée, Wim Magnus Fermi's golden rule is often invoked to obtain scattering rates due to imperfections for semi-classical transport in different condensed matter systems. As it is an estimate for relatively small perturbations, its validity depends on the system and imperfection properties under consideration. We present a formal way to obtain easy to handle validity criteria, based on general system parameters, e.g. system size and momentum of the electron states, and the statistical properties of the imperfections. The criteria can also be obtained with a simple set of Feynman rules and corresponding diagrams. We show concrete examples of validity criteria for electron transport in metallic nanowires with several elastic scattering mechanisms, e.g. point defect or grain boundary scattering. We observe realistic nanowire examples where the scattering rate appears to be valid but also cases where the criteria are clearly violated. The latter indicates that higher order effects come into play, such as electrons being trapped between grain boundaries or at a rough surface, which cannot be described using Fermi's golden rule. The presented validity criteria are therefore very useful to check whether or not the transport properties predicted by a semi-classical transport simulation can be trusted. [Preview Abstract] |
Monday, March 14, 2016 8:24AM - 8:36AM |
A24.00003: Parallel Quantum Circuit in a Tunnel Junction OMID FAIZY NAMARVAR, GHASSEN DRIDI, CHRISTIAN JOACHIM In between 2 metallic nanopads, adding identical and independent electron transfer paths in parallel increases the electronic effective coupling between the 2 nanopads through the quantum circuit defined by those paths. Measuring this increase of effective coupling using the tunnelling current intensity can lead for example for 2 paths in parallel to the now standard $G = G_1 + G_2 + 2 \sqrt{G_1.G_2}$ conductance superposition law (1). This is only valid for the tunnelling regime (2). For large electronic coupling to the nanopads (or at resonance), $G$ can saturate and even decay as a function of the number of parallel paths added in the quantum circuit (3). We provide here the explanation of this phenomenon: the measurement of the effective Rabi oscillation frequency using the current intensity is constrained by the normalization principle of quantum mechanics. This limits the quantum conductance $G$ for example to go when there is only one channel per metallic nanopads. This ef fect has important consequences for the design of Boolean logic gates at the atomic scale using atomic scale or intramolecular circuits.\\ \\ \textbf{References}:\\ (1) Joachim et al, Phys. Rev. B, 59, 16011 (1999).\\ (2) C. Joachim, Nature Nano.,7, 620 (2012).\\ (3) Sadeghi et al; PNAS 2015, 112, 9, 26 [Preview Abstract] |
Monday, March 14, 2016 8:36AM - 8:48AM |
A24.00004: Multi-channel quantum dragons from rectangular nanotubes with even-odd structure Godfred Inkoom, Mark Novotny Recently, a large class of nanostructures called quantum dragons have been discovered theoretically [1]. Quantum dragons are nanostuctures with correlated disorder but have an electron transmission probability $\mathcal{T}(E)$$=$$1$ for all energies $ E $ when connected to idealized leads. Hence for a single channel, the electrical conductance for a two-probe measurement should give the quantum of conductance $ G_{o}=\frac{2e^{2}}{h}$. The time independent Schr\"odinger equation for the single band tight binding model is solved exactly to obtain $ \mathcal{T}(E) $. We have generalized the matrix method and the mapping methods of [1] in order to study multi-channel quantum dragons for rectangular nanotubes with even-odd structure. The studies may be relevant for experimental rectangular nanotubes, such as MgO, copper phthalocyanine or some types of graphyne. [1] M.A. Novotny, Phys. Rev. B {\bf 90} 165103 [14 pages] (2014). [Preview Abstract] |
Monday, March 14, 2016 8:48AM - 9:00AM |
A24.00005: Effect of broadening in the weak coupling limit of vibrationally coupled electron transport through molecular junctions and the analogy to quantum dot circuit QED systems Rainer Hartle, Manas Kulkarni We [1] investigate the nonequilibrium population of a vibrational mode in the steady state of a biased molecular junction, using a rate equation approach. We focus on the limit of weak electronic-vibrational coupling and show that, in the resonant transport regime and for sufficiently high bias voltages, the level of vibrational excitation increases with decreasing coupling strength, assuming a finite and non-zero value. An analytic behavior with respect to the electronic-vibrational coupling strength is only observed if the influence of environmental degrees of freedom is explicitly taken into account. We consider the influence of three different types of broadening: hybridization with the electrodes, thermal fluctuations and the coupling to a thermal heat bath. Our results apply to vibrationally coupled electron transport through molecular junctions but also to quantum dots coupled to a microwave cavity, where the photon number can be expected to exhibit a similar behavior. [1] Rainer Hartle, Manas Kulkarni, Phys. Rev. B 91, 245429 (2015) [Preview Abstract] |
Monday, March 14, 2016 9:00AM - 9:12AM |
A24.00006: Landauer's formula with finite-time relaxation: Kramers' crossover in electronic transport Daniel Gruss, Kirill Velizhanin, Michael Zwolak Landauer's formula relates the conductance of a region of interest to its transmission probability. It is the standard theoretical tool to examine ballistic transport in nano- and meso-scale junctions and devices. This view of transport as transmission necessitates a simplified view of transmission, one occurring through an essentially fixed structure. Starting from a description of transport that includes relaxation of electrons in the reservoirs, we derive a Landauer-like formula for the steady-state current. We demonstrate that the finite relaxation time gives rise to three regimes of behavior. Weak relaxation within a small region nearby to the junction gives a contact limited current. Strong relaxation also influences the current by localizing electrons, distorting their natural dynamics and reducing the current. In an intermediate regime, the standard Landauer view is recovered. This behavior is analogous to Kramers' turnover in chemical reactions. [Preview Abstract] |
Monday, March 14, 2016 9:12AM - 9:24AM |
A24.00007: ABSTRACT WITHDRAWN |
Monday, March 14, 2016 9:24AM - 9:36AM |
A24.00008: Kondo-correlated transport in single molecule ferromagnetic break junction devices with controllable electrode magnetization alignment Gavin Scott, Ting-Chen Hu A quantum dot attached to electrodes with magnetizations that can be switched between parallel and anti-parallel alignment has been proposed as a platform for investigating quantum criticality associated with the destruction of Kondo entanglement. We have fabricated single molecule break junction devices with elliptical ferromagnetic electrodes designed to suit this purpose. Low temperature transport measurements, supported by micromagnetic simulations, were used to investigate the magnetoresistance response on control samples during the magnetization reversal process. We show results of Kondo-correlated transport as the source and drain contacts are switched between parallel and anti-parallel magnetization configurations. [Preview Abstract] |
Monday, March 14, 2016 9:36AM - 9:48AM |
A24.00009: Tuning Charge and Correlation Effects for a Single Molecule on a Graphene Device Hsin-Zon Tsai, Sebastian Wickenburg, Jiong Lu, Johannes Lischner, Arash A. Omrani, Alexander Riss, Christoph Karrasch, Han Sae Jung, Ramin Khajeh, Dillon Wong, Kenji Watanabe, Takashi Taniguchi, Alex Zettl, Steven G. Louie, Michael F. Crommie Controlling electronic devices down to the single molecule level is a grand challenge of nanotechnology. Single-molecules have been integrated into devices capable of tuning electronic response, but a drawback for these systems is that their microscopic structure remains unknown due to inability to image molecules in the junction region. Here we present a combined STM and nc-AFM study demonstrating gate-tunable control of the charge state of individual F4TCNQ molecules at the surface of a graphene field effect transistor. This is different from previous studies in that the Fermi level of the substrate was continuously tuned across the molecular orbital energy level. Using STS we have determined the resulting energy level evolution of the LUMO, its associated vibronic modes, and the graphene Dirac point (ED). We show that the energy difference between ED and the LUMO increases as EF is moved away from ED due to electron-electron interactions that renormalize the molecular quasiparticle energy. This is attributed to gate-tunable image-charge screening in graphene and corroborated by ab initio calculations. [Preview Abstract] |
Monday, March 14, 2016 9:48AM - 10:00AM |
A24.00010: Probing voltage induced bond rupture in a molecular junction Haixing Li, Timothy Su, Nathaniel Kim, Pierre Darancet, James Leighton, Michael Steigerwald, Colin Nuckolls, Latha Venkataraman We use scanning tunneling microscope break junction to study electric field breakdown at the single molecule level. We investigate breakdown phenomena in atomic chains composed of Si---Si, Si---O, Si---C, Ge---Ge and C---C bonds that are commonly found in the low-$\kappa$ dielectric material. We see different bond rupture behaviors in a range of molecular backbones, and use the results from a statistically large number of measurements to determine which bond breaks. We find that Si---Si and Ge---Ge bonds rupture above a 1V bias. We also find that the Si---C bond is more robust than Si---O or Si---Si bond at above 1V. Finally, we illustrate how an additional conductance pathway in parallel to the Si---Si bond changes bond rupture behavior under an electric field. We carry out ab initio calculations on these systems and demonstrate that the mechanism for bond rupture under electric field involves {\lq\lq}heating{\rq\rq} of the molecule through electron-vibrational mode coupling. [Preview Abstract] |
Monday, March 14, 2016 10:00AM - 10:12AM |
A24.00011: ABSTRACT WITHDRAWN |
Monday, March 14, 2016 10:12AM - 10:24AM |
A24.00012: Bias-dependent enhancement of the Fano factor in atomic-scale Au junctions Loah Stevens, Pavlo Zolotavin, Ruoyu Chen, Douglas Natelson We report measurements of current noise in STM-style Au break junctions at 77K, focusing on the dependence of the Fano factor on applied bias. In room temperature investigations of similar systems, measured noise at low bias (\textless 150 mV) was observed to agree well with Landauer-B\"{u}ttiker theory for shot noise at a fixed electronic temperature. At higher biases, however, measured noise exhibited a superlinear dependence on scaled bias above the low bias expectations. In the present experiment at cryogenic temperatures, we also observe this nonlinear increase of noise. We will discuss this behavior in terms of an enhancement of the Fano factor above the predicted model for minimum open transmission channels, and how the data constrain possible explanations of this excess noise. Furthermore, we will examine channel mixing in transport through the junction from measured Fano factor and conductance. [Preview Abstract] |
Monday, March 14, 2016 10:24AM - 10:36AM |
A24.00013: Electron Transport in Short Peptide Single Molecules Jing Cui, Joseph Brisendine, Fay Ng, Colin Nuckolls, Ronald Koder, Latha Venkarataman We present a study of the electron transport through a series of short peptides using scanning tunneling microscope-based break junction method. Our work is motivated by the need to gain a better understanding of how various levels of protein structure contribute to the remarkable capacity of proteins to transport charge in biophysical processes such as respiration and photosynthesis. We focus here on short mono, di and tri-peptides, and probe their conductance when bound to gold electrodes in a native buffer environment. We first show that these peptides can bind to gold through amine, carboxyl, thiol and methyl-sulfide termini. We then focus on two systems (glycine and alanine) and show that their conductance decays faster than alkanes terminated by the same linkers. Importantly, our results show that the peptide bond is less conductive than a sigma carbon-carbon bond. [Preview Abstract] |
Monday, March 14, 2016 10:36AM - 10:48AM |
A24.00014: Controlled fabrication of DNA molecular templates for the deposition and electrical measurement of 1D metal nanowires Jorge Barreda, Longqian Hu, Liuqi Yu, Zhibin Wang, Junfei Xia, Jingjiao Guan, Peng Xiong Stretched DNA nanowires (NWs) offer a convenient substrate for the fabrication and measurement of 1D metal NWs of width down to nm [1].So far the fabrication of the DNA templates has replied on somewhat random self-assembly processes. Here we demonstrate a process with high degree of control over the length, spacing, diameter , and orientation of the metal NWs: A one-step dewetting of a DNA solution on a PDMS stamp with an array of micropillars with well-defined pitch yields DNA NWs suspended across the micropillars along a chosen direction [2]. The DNA NWs are then transferred via micro-contact printing onto a Si/SiO2/SiNx substrate with a lithographically fabricated trench defined by an opening in the SiNx layer and undercut in the SiO2 layer. The template with DNA NWs stretched across the trench is placed in a high-vacuum evaporator for metal deposition, resulting in a metal NW of width defined by the diameter of the DNA template (\textless 10 nm) and length determined by the width of the trench. Quasi-four terminal I-V measurements are performed in situ with incremental metal deposition. Concomitant with a transition from strongly nonlinear IV to Ohmic behavior with increasing thickness, the NW resistance is observed to decrease exponentially. [1] Hopkins, David S., et al. Science 308.5729 (2005): 1762-1765. [2] Guan, Jingjiao, et al. Soft Matter 3.11 (2007): 1369-1371. [Preview Abstract] |
Monday, March 14, 2016 10:48AM - 11:00AM |
A24.00015: Electron field emission from Ge nanoclusters on Si. Veronika Burobina We analyzed the electron field emission from Ge nanoclusters grown on Si substrate by the method of molecular beam epitaxy. The emission properties were studied with the use of scanning tunneling microscopy. The phenomenological model of the field emission mechanism was applied to estimate current density from the surface of the pointed Ge/Si nanostructures. [Preview Abstract] |
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