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One-dimensional physics of interacting electrons and phonons in carbon nanotubes

Citation

Deshpande, Vikram Vijay (2009) One-dimensional physics of interacting electrons and phonons in carbon nanotubes. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-10312008-123250

Abstract

The one-dimensional (1D) world is quite different from its higher dimensional counterparts. For example, the electronic ground state in 1D is not a Fermi liquid as in most solids, due to the role of electron-electron interactions. Most commonly, electrons in 1D are described as a <i>Luttinger liquid</i>, where the low-energy excitations are decoupled bosonic charge and spin waves. Carbon nanotubes are clean 1D systems which have been shown to behave like a Luttinger liquid at high electron density. However, at low electron density and in the absence of disorder, the ground state is predicted to be a <i>1D Wigner crystal</i>—an electron solid dominated by long-range Coulomb interaction. Moreover, short-range interaction mediated by the atomic lattice (umklapp scattering) is predicted to transform a nominal 1D metal into a <i>Mott insulator</i>.

In this thesis, we develop techniques to make extremely clean nanotube single-electron transistors. We study them in the few-electron/hole regime using Coulomb blockade spectroscopy in a magnetic field. In semiconducting nanotubes, we map out the antiferromagnetic exchange coupling as a function of carrier number and find excellent agreement to a Wigner crystal model. In nominally metallic nanotubes, we observe a universal energy gap in addition to the single-particle bandgap, implying that nanotubes are never metallic. The magnitude, radius dependence and low-energy neutral excitations of this additional gap indicate a Mott insulating origin.

Further, we use simultaneous electrical and Raman spectroscopy measurements to study the phonons scattered by an electric current. At high bias, suspended nanotubes show striking negative differential conductance, attributed to non-equilibrium phonons. We directly observe such "hot" phonon populations in the Raman response and also report preferential electron coupling to one of two optical phonon modes. In addition, using spatially-resolved Raman spectroscopy, we obtain a wealth of local information including the 1D temperature profile, a spatial map of the thermal conductivity and thermal contact resistances, which reveal the mechanism of thermal transport in nanotubes.

Finally, with multi-wall nanotubes (MWNTs), we use electrical breakdown as thermometry to provide evidence for ballistic phonon propagation and obtain an estimate for the quantum of thermal conductance. We also develop linear-bearing nanoswitches using the low-friction properties of MWNTs.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:1D; ballistic phonons; carbon nanotubes; electron-electron interactions; electron-phonon interactions; linearing bearing; low-temperature transport experiments; Luttinger liquid; Mott insulator; nano-switch; one dimension; Raman spectroscopy; single electron transport; spatially-resolved; strongly correlated electrons; thermal transport; Wigner crystal
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Bockrath, Marc William
Thesis Committee:
  • Bockrath, Marc William (chair)
  • Refael, Gil
  • Atwater, Harry Albert
  • Eisenstein, James P.
Defense Date:15 September 2008
Record Number:CaltechETD:etd-10312008-123250
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-10312008-123250
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4349
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:29 May 2009
Last Modified:26 Dec 2012 03:07

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