Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Y5: Conductance and Coherence in Nanotubes and Nanobeams |
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Sponsoring Units: DCMP Chair: David Cobden, University of Washington Room: Portland Ballroom 256 |
Friday, March 19, 2010 8:00AM - 8:36AM |
Y5.00001: Field-effects and fractionalization in nanotubes and nanorings Invited Speaker: Magnetic and electric fields are a valuable means of probing the underlying physics of strongly correlated low dimensional systems. Here, the effect of fields is discussed in two instances of interacting electronic one- dimensional systems, both exhibiting ``fractionalization'' of the constituent electron degrees of freedom - i) The dramatic effects of transverse electric and magnetic fields on conduction properties of nanotubes is discussed.\footnote{DeGottardi et al., Phys. Rev. B 79, 205421 (2009)} It is shown that fields can yield controlled tuning of low-energy band structure properties such as inducing gaps in the spectrum, breaking various symmetries and altering Fermi velocities. Fields can strongly affect electron- electron interaction, yielding tunable Luttinger liquid physics, a means of accessing individual bands and the possibility of spin- charge-band separation. ii) The magnetic field profile around a nanoscale conducting ring is explored. The geometry is geared to investigate coherence properties of fractionalized electrons reported to have been recently observed in quantum wires.\footnote {Steinberg et al., Nature Physics 4, 116 (2008)} It is shown that the magnetic landscape provides a non-invasive probe for mapping the manner in which an electron injected into the ring splinters into two parts. [Preview Abstract] |
Friday, March 19, 2010 8:36AM - 9:12AM |
Y5.00002: Spin and charge transport in a carbon nanotube spin diode Invited Speaker: I will describe the measurements of asymmetric conductance and the current shot noise through a carbon nanotube quantum dot with one ferromagnetic and one normal-metal lead. The observed asymmetry is spin-dependent, and stems from the interplay between the spin accumulation and the Coulomb blockade on the quantum dot. The results imply that the current is spin-polarized for one direction of the bias, and that the degree of spin polarization is fully and precisely tunable using the gate and bias voltages. As the operation of this spin diode does not require magnetic fields or optics, it could be used as a building block for electrically controlled spintronic devices. [Preview Abstract] |
Friday, March 19, 2010 9:12AM - 9:48AM |
Y5.00003: Sagnac Interference in Carbon Nanotube Loops Invited Speaker: The Sagnac effect describes, historically, the interference between two counter-propagating coherent light beams that transverse a rotating loop. The same effect can also be realized in Carbon nanotube loops, where instead of rotation, the interference is generated due to a small detuning of the right- and left-moving electron velocities: 2u=vR-vL. The Sagnac interference in Carbon nanotubes is expected to persist even when temperature effects obliterate all other interference signatures (e.g., Fabry-Perot). In this talk I we explore this remarkable interference mode, and discuss the dependence of the Sagnac conductance oscillations on temperature and interactions. [Preview Abstract] |
Friday, March 19, 2010 9:48AM - 10:24AM |
Y5.00004: New aspects of the metal-insulator transition in vanadium dioxide nanobeams Invited Speaker: The fundamental properties of the famous metal-insulator phase transition in vanadium dioxide are obscured in traditional samples by domain structure. In contrast, single-crystal nanobeams of the material can be prepared in such a way that the frustration is absent, and the stress is zero or almost uniform, even while the transition is taking place. Studying nanobeams using a combination of transport and optical methods has allowed us to obtain a number of new results, including the following. First, the uniform metallic phase can be dramatically supercooled. Second, the so-called M2 insulating phase shows a temperature-independent resistivity at the transition, implicating electron-electron interactions in the controlling mechanism. Third, the M1 and M2 insulating phases have the same thermal electronic gap. Fourth, we establish a new phase diagram of the material as a function of stress along the rutile c-axis which helps to explain a number of recent experiments and some anomalies in the older literature. Work done in collaboration with Jiang Wei, Jae Park, Vinny Roma, Andrew Jones, Sam Berweger, and Markus Raschke. [Preview Abstract] |
Friday, March 19, 2010 10:24AM - 11:00AM |
Y5.00005: DNA Sequence Motifs for Structure-Specific Recognition and Separation of Carbon Nanotubes Invited Speaker: Single walled carbon nanotubes (SWCNT) are a family of molecules that have the same cylindrical shape but different chiralities. The SWNT sorting problem, i.e., separation of a synthetic mixture of tubes into individual single-chirality components, has attracted considerable attention in recent years. A systematic and general method to purify each and every single-chirality species of the same electronic type from the synthetic mixture is highly desirable. Recently, we have reported such a method that allows purification of all 12 major single-chirality semiconducting species from a synthetic mixture, with sufficient yield for both fundamental studies and application development (Tu \textit{et al}., \textbf{\textit{Nature}}, 406, 250, 2009). In this presentation, I will review the experimental development and mechanistic understanding of the separation process. In particular, a model of DNA wrapping structure invoking a novel secondary DNA structure motif will be discussed. [Preview Abstract] |
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