Young-Gui Yoon

Disorder, Pseudospins, and Backscattering in Carbon Nanotubes

We address the effects of disorder on the conducting properties of metal and semiconducting carbon nanotubes. Experimentally, the mean free path is found to be much larger in metallic tubes than in doped semiconducting tubes. We show that this result can be understood theoretically if the disorder potential is long ranged. The effects of a pseudospin index that describes the internal sublattice structure of the states lead to a suppression of scattering in metallic tubes, but not in semiconducting tubes. This conclusion is supported by tight-binding calculations.

Confinement-Induced Glassy Dynamics in a Model for Chromosome Organization.

Recent experiments showing scaling of the intrachromosomal contact probability, P(s)∼s(-1) with the genomic distance s, are interpreted to mean a self-similar fractal-like chromosome organization. However, scaling of P(s) varies across organisms, requiring an explanation. We illustrate dynamical arrest in a highly confined space as a discriminating marker for genome organization, by modeling chromosomes inside a nucleus as a homopolymer confined to a sphere of varying sizes. Brownian dynamics simulations show that the chain dynamics slows down as the polymer volume fraction (ϕ) inside the confinement approaches a critical value ϕ(c). The universal value of ϕ(c)(∞)≈0.44 for a sufficiently long polymer (N≫1) allows us to discuss genome dynamics using ϕ as the sole parameter. Our study shows that the onset of glassy dynamics is the reason for the segregated chromosome organization in humans (N≈3×10(9), ϕ≳ϕ(c)(∞)), whereas chromosomes of budding yeast (N≈10(8), ϕ

Quantum conductance of carbon nanotube peapods

We present a first-principles study of the quantum conductance of hybrid nanotube systems consisting of single-walled carbon nanotubes (SWCNTs) encapsulating either an isolated single C60 molecule or a chain of C60 molecules (nanotube peapods). The calculations show a rather weak bonding interaction between the fullerenes and the SWCNTs. The conductance of a (10,10) SWCNT with a single C60 molecule is virtually unaffected at the Fermi level, but exhibits quantized resonant reductions at the molecular levels. The nanotube peapod arrangement gives rise to high density of states for the fullerene highest occupied molecular orbital and lowest unoccupied molecular orbital bands.

Electronic Structure and Quantum Conductance of Carbon Nanotubes

The unique electronic properties of carbon nanotubes stem from the fact that the electronic structure of these systems is derived from a folded graphene band structure which is highly sensitive to the tube diameter and chirality. In this chapter, we review some theoretical work on the electronic and transport properties of the single-walled carbon nanotubes, including systems with junction structures, defects, and disorder. On-tube metal-metal, semiconductor-semiconductor, and metalsemiconductor junctions have been studied. In addition, substitutional impurities and pentagon-heptagon defect pairs are shown to have interesting effects on the conductance. The structure and properties of crossed nanotube junctions and disordered nanotubes with static external perturbations have also been studied. The nanoscale size and the unique electronic properties of the carbon nanotubes make the potential usage of these novel systems for new device applications very promising.