Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session V5: Invited Symposium: Transport in Single Molecules |
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Sponsoring Units: DMP Chair: Mark Hybertsen, Columbia University Room: LACC 502B |
Thursday, March 24, 2005 11:15AM - 11:51AM |
V5.00001: Vibrational states and Kondo physics in single-molecule transistors Invited Speaker: It is now possible to fabricate a transistor with a channel consisting of a single small molecule. While electronic transport through such a device resembles that seen in metal and semiconductor single-electron transistors, single-molecule transistors (SMTs) can tie together concepts from chemical electron transfer theory and many-body physics. I will describe our recent observations of inelastic cotunneling features in SMTs that correspond with vibrational excitations of the molecule, as determined by Raman and infrared spectroscopy. These vibrational features evolve in a nontrivial manner as a function of gate voltage when electronic levels are nearly resonant with the vibrational energies. When the molecule contains an unpaired electron, we also see vibrational satellite features around the Kondo resonance. This demonstrates that SMTs are rich systems for studying the interplay of electronic correlations and vibrational motion. This work was supported by NSF DMR-0347253, the Packard Foundation, the Research Corporation, and the Welch Foundation. [Preview Abstract] |
Thursday, March 24, 2005 11:51AM - 12:27PM |
V5.00002: Current-induced mechanical effects in nanoscale junctions Invited Speaker: Transport of electrical charge across a nanoscale junction is accompanied by many effects like transfer of energy between electrons and ions [1] and consequent heating of the junction [2], and forces on ions due to current-induced variations of the electronic distribution [3]. I will discuss these effects in atomic and molecular wires and focus on their description at the atomic level. In particular, I will discuss their relative role in the stability of nanojunctions and compare these findings with experimental results. Work supported by NSF. [1] Y-C. Chen, M. Zwolak and M. Di Ventra, “Inelastic current-voltage characteristics of atomic and molecular junctions”, Nano Lett. 4, 1709 (2004). [2] Y-C. Chen, M. Zwolak and M. Di Ventra, “Local heating in nanoscale conductors”, Nano Lett. 3, 1691 (2003). [3] Z. Yang, M. Chshiev, M. Zwolak, Y.-C. Chen, and M. Di Ventra “Role of heating and current-induced forces in the stability of atomic wires”, cond-mat/0409772. [Preview Abstract] |
Thursday, March 24, 2005 12:27PM - 1:03PM |
V5.00003: Vibronically Mediated Conductance Gated by Charging of a Single Impurity Complex Invited Speaker: The electronic properties of single C$_{60}$ molecules, C$_{60}$ monolayer, and alkali doped C$_{60}$ adsorbed on Al$_{2}$O$_{3}$ grown on NiAl(110) have been studied by STM spectroscopy and microscopy. Due to the unique double barrier tunneling junction (DBTJ) configuration, consisting of the vacuum and oxide barriers, interesting phenomena such as vibronic progressions, bipolar transport, and conductance gated by single impurity charging were observed. These results provide valuable information on the electron-phonon interaction, molecular conductance, and the role of impurities in nanoscale electron transport. [Preview Abstract] |
Thursday, March 24, 2005 1:03PM - 1:39PM |
V5.00004: Theoretical study of vibrational effects in molecular transistors Invited Speaker: Molecular devices raise the fundamental issue of non- equilibrium quantum mechanics of strongly correlated systems. This talk presents a complete theory of a model system (resonant level coupled to leads and a local oscillator) which captures an essential aspect of molecular devices and provides a context for strong correlation physics. The limits of high temperature (all coupling) and weak coupling (all temperatures) are treated by standard rate equation and Keldysh diagrammatic methods. Saddle point methods are developed for the more challenging low temperature strong coupling regime. The key issue is the formulation and solution of rate equations for the steady state reduced density matrix. Solutions of non- equilibrium mean field equations are shown to correspond to the field values at which the density matrix is peaked in a semiclassical limit. If multiple solutions exist, all are found to make non-vanishing contributions to physical quantities, implying absence of bistability in the current but structure in the noise. Departures from equilibrium produce decoherence that prevents the formation of characteristically quantal features such as the polaron peak in the spectral function. Generalizations of the method to other strongly correlated systems such as the non-equilibrium Kondo model will be given. Ref: Phys. Rev. B 69, 245302 (2004) and cond-mat/0409248. This work was performed in collaboration with Igor Aleiner and Andrew Millis and was supported primarily by the Nanoscale Science and Engineering Initiative of the National Science Foundation under NSF Award Number CHE-0117752 and by the New York State Office of Science, Technology, and Academic Research (NYSTAR). [Preview Abstract] |
Thursday, March 24, 2005 1:39PM - 2:15PM |
V5.00005: Tuning Fullerene Electronic Properties: From Single Molecules to Extended Monolayers Invited Speaker: Fullerenes provide powerful building blocks for creating nanostructures with unique electronic properties due to their flexible electronic structure. This behavior arises through a combination of molecular energy levels, intramolecular Coulomb forces, electron-phonon coupling, and local charging. When molecules are placed at an interface, substrate charge transfer and screening effects also play an important role. We have used cryogenic scanning tunneling spectroscopy to examine the interplay of these factors in determining molecular electronic structure from the single molecule regime all the way up to the full monolayer regime. We find that it is possible to reversibly change the charge state of individual fullerenes through single-atom doping, and we have examined how molecular electronic structure is influenced by extended monolayer formation and surface screening effects. We observe strong variations in local molecular electronic structure due to charge doping, and in local electron-phonon coupling due to fullerene composition. [Preview Abstract] |
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