Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session W26: Focus Session: Charge Transport in Nanostructures III |
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Sponsoring Units: DCP Chair: Mark Ratner, Northwestern University Room: Colorado Convention Center 205 |
Thursday, March 8, 2007 2:30PM - 3:06PM |
W26.00001: Magneto-Resistance of Nanoscale Molecular Devices Invited Speaker: Affecting the current through a molecular or a nano-scale junction is usually done by a combination of bias and gate voltages. Magnetic fields are less studied because nano-devices can capture only low values of the magnetic flux. Here, I review our recent theoretical work on the use of magnetic fields as gates for such junctions. Several plausible model systems of such devices will be presented, such as the quantum corral, carbon nanotubes and polycyclic aromatic hydrocarbon molecules. Despite the similarly between gating properties of the magnetic and electric fields, we find that there are also striking differences. This will be illustrated for a multi-terminal device, where the polarity of the magnetic field plays a key role, and with respect to inelastic effects, where the conductance as a function of the gate voltage broadens upon coupling to phonons while it actually narrows considerably in response to a magnetic field. [Preview Abstract] |
Thursday, March 8, 2007 3:06PM - 3:18PM |
W26.00002: Shot Noise in Single-Molecule Transistors Zachary Keane, Douglas Natelson While single-molecule electronic devices have been studied extensively, both experimentally and theoretically, a detailed understanding of the physics of charge transport through molecules is still lacking. Recent experiments have shown that it is feasible to measure shot noise in mechanically fabricated single-molecule transistors. Shot noise is a particularly interesting measurement in that it has the potential to reveal details about the correlations between electrons as they cross a molecule. In devices known to exhibit strong correlated-electron effects (e.g. in the Kondo regime), shot noise measurements could provide useful guidance to theorists as they attempt to develop working models for electron transport. We present preliminary results of noise measurements in three-terminal single-molecule devices fabricated by electromigration. [Preview Abstract] |
Thursday, March 8, 2007 3:18PM - 3:30PM |
W26.00003: Magnetoconductance of molecularly linked Au nanoparticle arrays near the metal-insulator transition Al-Amin Dhirani, Jeff Dunford, Brian Statt Magnetoconductance of 1,4-butanedithiol-linked Au nanoparticle films reveal features consistent with ``weak localization'' (coherent backscattering). Elastic, inelastic, and spin-orbit-scattering time scales extracted using a theoretical model are consistent with those found in other studies on granular Au films, and in particular, reveal that elastic-scattering time scales are comparable to those required for an electron to traverse a nanoparticle. The latter result is consistent with non-Arrhenius conductance vs temperature data. Together, the data suggest that scattering within clusters of molecularly linked nanoparticles plays a critical role in hopping-electron transport in films near a percolationdriven metal-insulator transition. [Preview Abstract] |
Thursday, March 8, 2007 3:30PM - 3:42PM |
W26.00004: Metal to Insulator Transition in Films of Molecularly Linked Gold Nanoparticles Amir Zabet-Khosousi, Al-Amin Dhirani Self-assembled structures comprising nanoparticles (NPs) and molecular linkers exhibit remarkable electronic behaviours ranging from insulating to metallic. These behaviours can be controlled via chemical synthesis and choice of linker molecules. However, charge transport through these structures is not well understood. Here, we report a metal-insulator transition (MIT) in films of alkanedithiol (C$_{n}$S$_{2})$-linked gold NPs, as the length of linkers ($n)$ is systematically varied. Our results provide strong evidence for a MIT occurring at $n$ = 5. We describe these results in a context of a Mott-Hubbard model. We find that all insulating samples ($n \quad \ge $ 5) exhibit a universal scaling behaviour $R \sim $ exp[($T_{0}$/$T)^{p}$] (where $R$ is resistance, $T$ is temperature, $T_{0}$ is a fitting parameter and $p$ = 0.65), and all metallic samples ($n \le $ 5) exhibit weaker $R$--$T$ dependencies than bulk gold. We discuss these observations in terms of competitive thermally-activated processes and strong $T$-independent elastic scattering, respectively. [Preview Abstract] |
Thursday, March 8, 2007 3:42PM - 3:54PM |
W26.00005: Theoretical study of molecule mediated spin-polarized electron tunneling between magnetic materials Haiying He, Ravindra Pandey, Shashi Karna There has been a recent interest in organic molecule-mediated spin-polarized electron transport with a potential application in molecular-scale spintronics. In this presentation, we present the results of a theoretical study on the spin-dependent electron tunneling via a self-assembled monolayer of $\sigma $-bonded bicyclo[2.2.2]octane-1,4-dithiol on Ni(111). Comparison with a similar study involving $\pi $-conjugated molecules, suggests that the magnitude of the tunnel current and the spin-dependent current are strongly influenced by the nature of chemical bonds in the molecular structure. It gives further understanding of the role of the organic molecules on the spin-polarization of electron transport and provides a basic guideline in choice of molecules in this respect. [Preview Abstract] |
Thursday, March 8, 2007 3:54PM - 4:06PM |
W26.00006: Influence of Correlated Hybridization on the Conductance of Molecular Transistors Jong-Chin Lin, Frithjof Anders, Daniel Cox We study the spin-1/2 single-channel Anderson impurity model with correlated (occupancy dependent) hybridization for molecular transistors using the numerical renormalization-group method. Correlated hybridization can induce nonuniversal deviations in the normalized zero-bias conductance and, for some parameters, modestly enhance the spin polarization of currents in applied magnetic field. Correlated hybridization can also explain a gate-voltage dependence to the Kondo scale similar to what has been observed in recent experiments. [Preview Abstract] |
Thursday, March 8, 2007 4:06PM - 4:18PM |
W26.00007: Path integral simulations of quantized conductance in nanowires John Shumway, Matthew Gilbert Theoretical studies of spin and charge transport in nanostructure often include interactions perturbatively or at a mean-field level. In some cases it is desirable to have a fully quantum many-body method to describe the interacting system: such is the case when investigating spin ordering near the ``0.7-structure'' in quantum point contacts or for simulating systems with strong polaronic effects. We have developed a new path-integral quantum Monte Carlo (QMC) approach to transport. Previous QMC simulations have been valued for accurately treating electronic correlation in quantum dot spectroscopy---this work now opens up many new opportunities for simulating quantum transport. We show simulation data demonstrating how current-current correlation functions in the Kubo formalism lead to quantization of conductance in GaAs nanowires. This new, finite-temperature, many-body computation technique should have many uses in the study of quantum wires and molecular electronics. [Preview Abstract] |
Thursday, March 8, 2007 4:18PM - 4:30PM |
W26.00008: Ab-initio study of transport in the Coulomb-blockade regime Haitao Wang, Osamu Hino, Garnet Chan Here we report a new ab-initio model for molecular conductance in the Coulomb blockade regime using unrestricted Hartree-Fock theory within the non-equilibrium Greens function (NEGF) formalism. We demonstrate calculations on recent experimentally studied transition metal complexes, studying the effect of gating on current and the corresponding Coulomb blockade effects. [Preview Abstract] |
Thursday, March 8, 2007 4:30PM - 4:42PM |
W26.00009: Non-Markovian Transport of Charges in Solid-State Quantum Dots e. Ying-Tsan Tang, Yueh-Nan Chen, Brandes Tobias, Der-San Chuu The population dynamics of an electron in a double-dot system coupled to reservoirs is theoretically investigated. Basically, as we put an extra single dot that is strongly coupled to the extended reservoir, it would be possible for experimentalists to realize their modification of coupling strength; therefore we could properly control the memorial effect between system and reservoir by extra coupling. Throughout this study, we effectively change the decay of the entire system. Moreover, the exact results for non-Markovian couplings to both phonon and electron reservoirs with structured tunneling density of states are obtained, which contains the coherent states created by the distance of double dot embedding in the same system as well as the energy shift caused by purely electron-phonon coupling. Eventually, the relaxation dynamics of the Zeno or Anti-Zeno effect reveals insight into the defined decay rate. [Preview Abstract] |
Thursday, March 8, 2007 4:42PM - 4:54PM |
W26.00010: Controlled production and electronic characterization of defects in carbon nanotubes Brett Goldsmith, Vaikunth Khalap, Alexander Kane, Philip Collins Electrochemical functionalization of nanotubes allows fine control of the number of functionalized sites on a nanotube down to the limit of single, point functionalizations in otherwise pristine devices. This presentation will describe the local and 2-terminal electronic properties of the resulting devices. Point-functionalized devices exhibit spatially-localized resistance as mapped by scanning Kelvin probe microscopy and local gate sensitivity associated with the chemical disorder. The findings are reinforced by further attachment of specific chemical markers visible to electron microscopy. [Preview Abstract] |
Thursday, March 8, 2007 4:54PM - 5:30PM |
W26.00011: Electrons, holes, and electron-hole junctions in carbon nanotubes Invited Speaker: Carbon nanotubes possess an unusual band structure consisting of symmetric electron and hole subbands separated by a gap determined by the nanotube's chirality, diameter and any external perturbations. Here, we study the properties of both electrons and holes in these one-dimensional subbands. Capacitance measurements are used to directly probe the van Have singularities in the density of states and the energies of the electron and hole subbbands[1]. Electrical[2] and photocurrent measurements are employed to investigate the properties of nanotube p-n junctions. These measurements directly yield the nanotube bandgap and show fascinating step-like behavior in the reverse-bias region. Finally, measurements of p-n-p nanotube quantum dots are presented where the bandgap is tuned to zero by an external magnetic field. These experiments illustrate just a few of the exciting opportunities available in electron-hole nanotube devices. [1] S. Ilani, L.A. Donev, M. Kinderman, and P.L. McEuen, Nature Physics 2, 687 (2006). [2] K. Bosnick, N. Gabor, and P. L. McEuen; Appl. Phys. Lett. 89, 163121 (2006) [Preview Abstract] |
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