Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session B20: Focus Session: Mesoscopics - Transport |
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Sponsoring Units: DMP Chair: Yvan Bruynseraede, Catholic University-Leuven, Belgium Room: 322 |
Monday, March 18, 2013 11:15AM - 11:51AM |
B20.00001: From Quanta to the Continuum: Opportunities for Mesoscale Science Invited Speaker: John Sarrao Mesoscale science embraces the regime where atomic granularity and quantization of energy yield to continuous matter and energy, collective behavior reaches its full potential, defects, fluctuations and statistical variation emerge, interacting degrees of freedom create new phenomena, and homogeneous behavior gives way to heterogeneous structure and dynamics. Mesoscale architectures form a hierarchy extending from atoms and molecules through polymers, supramolecular assemblies, periodic lattices, multilayers, nanocrystal arrays and multiphase materials. Mesoscale science builds on the foundation of nanoscale knowledge and tools that the community has developed over the last decade and continues to develop. Mesoscale phenomena offer a new scientific opportunity: designing architectures and interactions among nanoscale units to create new macroscopic behavior and functionality. Examples of mesoscale successes, challenges and opportunities will be described. A more complete discussion of mesoscale science can be found in the BESAC report, \textit{From Quanta to the Continuum: Opportunities for Mesoscale Science}, http://science.energy.gov/bes/news-and-resources/reports/basic-research-needs/ Innovative community input on opportunities for mesoscale science can be found on the \textit{Mesoscopic Materials and Chemistry} website, http://www.meso2012.com/ [Preview Abstract] |
Monday, March 18, 2013 11:51AM - 12:03PM |
B20.00002: Magnetoresistance Jumps in Mesoscopic Hybrid Devices Ali C. Basaran, Carlos Monton, Juan Pereiro, Ivan K. Schuller We have studied the electrical transport of superconducting stripes (Nb and V) with periodically altered local magnetization. The local magnetization is controlled by the ferromagnetic states of Ni rings placed on top of the stripes. We observe a series of large resistance jumps as a function of external magnetic field (Ha). The jumps occur at temperature and current density dependent Ha values which indicate that they are probably not related to vortex pinning. Resistance jumps along with observed multiple steps in the current-voltage characteristics could be attributed to weak links induced by magnetic stray field or proximity effects originated by Ni rings in the superconducting area. The exact origin of these jumps is still under investigation. [Preview Abstract] |
Monday, March 18, 2013 12:03PM - 12:15PM |
B20.00003: Electron transport in confined oxide nanowires Guanglei Cheng, Michelle Tomczyk, Shicheng Lu, Mengchen Huang, Josh Veazey, Patrick Irvin, Chang-Beom Eom, Jeremy Levy The invention of conductive AFM lithography at the LaAlO$_3$/SrTiO$_3$ interface enables the creation of clean inter-connected oxide nanowires and artificially engineered tunnel barriers. Here we create an oxide nanowire that is confined by two tunnel barriers using this technique. Two terminal and four terminal transport studies reveal transitions among Cooper pair tunneling, Coulomb blockade and Fabry-Perot inteference that can be tuned by side gate voltages and external magnetic field. Our results indicate the presence of long-range coherence in LaAlO$_3$/SrTiO$_3$ nanowires. [Preview Abstract] |
Monday, March 18, 2013 12:15PM - 12:27PM |
B20.00004: Electric transport in Individual GaAs nanowires Zhuting Sun, Andrei Kogan, Tim Burgess, Chenupati Jagadish We report electrical transport measurements on individual GaAs nanowires approximately 50 nm in diameter contacted via lithographically patterned Al/Ti metal films. The nonlinear current-voltage characteristics show a strongly hysteretic behavior sensitive to the device temperature and the biasing history. In hysteresis-free regimes, we compare the data to a model based on two metal-semiconductor barriers in series with the wire, and find a good overall agreement. We also discuss the effects of surface treatments on the metal-wire interface resistance. The work is supported by NSF grant DMR-1206784 and DMR-0804199 and University of Cincinnati. [Preview Abstract] |
Monday, March 18, 2013 12:27PM - 12:39PM |
B20.00005: Coherent electron transport in InAs nanowires Marion J. L. Sourribes, Ivan Isakov, Marina Panfilova, Daniele Ercolani, Francesco Giazotto, Lucia Sorba, Paul A. Warburton Indium arsenide nanowires are of special interest since they exhibit high mobility, strong spin-orbit coupling and form ohmic contacts with metals which make them good candidates for the observation of Majorana fermions in semiconductor/superconductor hybrid systems. InAs nanowires have already been used as Josephson elements in superconducting devices. Here we report our low-temperature experiments on InAs nanowires grown by two methods: (i) gold-catalyzed chemical beam epitaxy on InAs (111) substrates; (ii) catalyst-free molecular beam epitaxy on Si (111) substrates. Contacts to the nanowires are defined by e-beam lithography. Before metallization of the contacts, the nanowire surface is deoxidized by an in situ sputter-cleaning process leading to a specific contact resistance of $9.8\times10^{-9}\,\Omega$.cm$^{2}$. These highly transparent contacts allowed the observation of proximity-induced superconductivity in InAs nanowires connected with Nb contacts. The critical current was tuned by changing the gate voltage. Both magnetic-field-dependent and gate-voltage-dependent measurements of universal conductance fluctuations were performed to extract information on the electron phase coherence. [Preview Abstract] |
Monday, March 18, 2013 12:39PM - 12:51PM |
B20.00006: End and Side Contacts to NiSi nanowires Abdel F. Isakovic, A. Belkadi NiSi nanowires were nanofabricated with end and side contacts. These contacts are designed to minimize spreading resistance and are tested to check whether they can aid in decreasing the energy cost of current injection and current ejection in nanotransport. It is demonstrated that the end contacts have lower power in 1/f noise spectrum. Transport data (current-voltage, differential resistance) also show quantitative differences from ``standard'' bottom or top contacts to SiNi nanowires, indicating that the presence of edge- and end-states at the termination points of the nanowires gives rise to different transport conditions. Time-dependent correlation coefficient from noise spectra is determined and it is different for different types of contacts. Structural study of nanowires contacted in this manner is also presented. [Preview Abstract] |
Monday, March 18, 2013 12:51PM - 1:03PM |
B20.00007: Strain manipulated direct-indirect band gap transition in GaAs nanowires Xihong Peng, Andrew Copple, Nathaniel Ralston One dimensional nanostructures of group III-V semiconductors have drawn broad research interests in recent years due to their potential applications in nano-electronics. In particular, GaAs has been considered as a promising channel material for the high speed NMOS beyond Si based technology. In this project, electronic structures of GaAs nanowires at both wurtzite and zinc blende phases were studied using first-principles Density Functional Theory (DFT) calculations. It was found that the band gap of GaAs nanowires experience a direct-to-indirect transition when the diameter of the nanowires is smaller than a specific value [1]. For those thin GaAs nanowires with an indirect band gap, it was found that the gap can be tuned to be direct if a moderate external strain is applied. We found many types of strains, such as tensile and compressive uniaxial strain, radial strain, strain along a specific orientation in the cross-section of the nanowires, can trigger the indirect-to-direct gap transition. The critical strains for the gap-transition are determined by the energy crossover of two states in conduction bands. \\[4pt] [1] A. Copple, N. Ralston, X.-H. Peng, Appl. Phys. Lett.100, 193108 (2012). [Preview Abstract] |
Monday, March 18, 2013 1:03PM - 1:15PM |
B20.00008: Local transport measurement at mesoscopic lengthscales on epitaxial graphene using scanning tunneling potentiometry Weigang Wang, Ko Munakata, Michael Rozler, Malcolm R. Beasley We report direct measurement of the local transport potential at mesoscopic lengthscales in epitaxial graphene by scanning tunneling potentiometry. The measurements were made possible by using slender, sharp tips manufactured by focused ion beam that avoid the previous problem of tip jumping. The sample was measured at 17K, well below the onset of weak localization; hence locally the transport was mesoscopic. Besides local Landauer residual resistivity dipoles associated with topographical features of our sample, we observed peaks and dips in the local transport potential for which there is as yet no explanation. Work supported by AFOSR MURI Contract {\#}~FA9550-09-1-0583-P00006 [Preview Abstract] |
Monday, March 18, 2013 1:15PM - 1:27PM |
B20.00009: ABSTRACT HAS BEEN MOVED TO V1.00314 |
Monday, March 18, 2013 1:27PM - 1:39PM |
B20.00010: Probing spin-charge relation by magnetoconductance in one-dimensional polymer nanofibers Yung Woo Park Polymer nanofibers are one dimensional (1-D) organic hydrocarbon systems containing conducting polymers where the non-linear local excitations such as solitons, polarons and bipolarons formed by the electron-phonon interaction were predicted. Magnetoconductance (MC) can simultaneously probe both the spin and charge of these mobile species and identify the effects of electron-electron interactions on these nonlinear excitations. Here we report our observations of a qualitatively different MC in polyacetylene (PA) and in polyaniline (PANI) and polythiophene (PT) nanofibers. In PA the MC is essentially zero, but it is present in PANI and PT. The universal scaling behavior and the zero (finite) MC in PA (PANI and PT) nanofibers provide evidence of Coulomb interactions between spinless charged solitons (interacting polarons which carry both spin and charge). [Preview Abstract] |
Monday, March 18, 2013 1:39PM - 1:51PM |
B20.00011: On the Lifetimes of Nonaxisymmetirc Metallic Nanowires Lan Gong, Jerome Buerki, Charles Stafford, Daniel Stein We present a theoretical approach for understanding the stability of simple metallic nanowires, in particular monovalent metals such as the alkalis and noble metals. Their cross sections are of order one nanometer so that small perturbations from external (usually thermal) noise can cause large geometrical deformations. The nanowire lifetime is defined as the time required for making a transition into a state with different cross-sectional geometry. This can be a simple overall change in radius, or a quadrupolar deformation, or both. We develop a stochastic field theoretical model to describe this noise-induced transition process, in which the initial and final states correspond to locally stable states on a potential surface derived numerically from a nearly free electron model. The numerical ``string method" is implemented to determine the optimal transition path governing the lifetime. Using these results, we tabulate the lifetimes of sodium and gold nanowires of several different initial geometries. [Preview Abstract] |
Monday, March 18, 2013 1:51PM - 2:03PM |
B20.00012: Making quantum devices with electrical properties that are robust to thermal cycling using AlGaAs/GaAs HIGFET structures Adam Micolich, Andrew See, Oleh Klochan, Adam Burke, Alex Hamilton, Ian Pilgrim, Billy Scannell, Rick Montgomery, Richard Taylor, Martin Aagesen, Poul Lindelof, Ian Farrer, David Ritchie The transport properties of quantum devices on modulation-doped AlGaAs/GaAs heterostructures change after thermal cycling above $\sim$130 K due to charge redistribution in the modulation doping layer. This is particularly evident in a quantum dot's magnetoconductance fluctuations (MCF) which provide a sensitive fingerprint of electron trajectories through the dot. We show that the MCF become reproducible with high-fidelity after thermal cycling to 300 K in quantum dots made using AlGaAs/GaAs heterostructures without modulation doping. This is achieved by populating the dot electrostatically using a Heterostructure Insulated Gate Field Effect Transistor (HIGFET) architecture. Our result demonstrates ionized impurity scattering has a measurable effect on transport in quantum dots, even in the ballistic transport regime. It highlights the potential for HIGFET-based architectures to provide devices with significantly reduced small-angle scattering at equivalent transport mobility, and more thermally robust electrical properties. More broadly, we suggest a quantum dot's MCF may be a useful tool for studying the temporal/thermal stability of disorder in other semiconductor materials. [Preview Abstract] |
Monday, March 18, 2013 2:03PM - 2:15PM |
B20.00013: Scattering phase of quantum dots: Emergence of universal behavior Philippe Jacquod, Rodolfo Jalabert, Rafael Molina, Dietmar Weinmann We investigate scattering through chaotic ballistic quantum dots in the Coulomb-blockade regime. Focusing on the scattering phase, we show that long universal sequences emerge in the short wavelength limit of many electrons on the dot, where phase lapses of $\pi$ systematically occur in between two consecutive resonances. We further argue that such universal sequences become shorter and shorter as the wavelength becomes larger/the number of electrons on the dot is reduced. Our results are corroborated by numerics and are in qualitative and quantitative agreement with experimental results. We finally present numerical data on models of interacting electrons to show that strong correlations do not alter our conclusions. [Preview Abstract] |
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