125 research outputs found
Transport in Nanotubes: Effect of Remote Impurity Scattering
Theory of the remote Coulomb impurity scattering in single--wall carbon
nanotubes is developed within one--electron approximation. Boltzmann equation
is solved within drift--diffusion model to obtain the tube conductivity. The
conductivity depends on the type of the nanotube bandstructure (metal or
semiconductor) and on the electron Fermi level. We found exponential dependence
of the conductivity on the Fermi energy due to the Coulomb scattering rate has
a strong dependence on the momentum transfer. We calculate intra-- and
inter--subband scattering rates and present general expressions for the
conductivity. Numerical results, as well as obtained analytical expressions,
show that the degenerately doped semiconductor tubes may have very high
mobility unless the doping level becomes too high and the inter--subband
transitions impede the electron transport.Comment: 13 pages, 4 figure
Electronic response and bandstructure modulation of carbon nanotubes in a transverse electrical field
The electronic properties of carbon nanotubes in a uniform transverse field
are investigated within a single orbital tight-binding model. For doped
nanotubes, the dielectric function is found to depend not only on symmetry of
the tube, but also on radius and Fermi level position. Bandgap opening/closing
is predicted for zigzag tubes, while it is found that armchair tubes always
remain metallic, which is explained by the symmetry in their configuration. The
bandstructures for both types are considerably modified when the field strength
is large enough to mix neighboring subbands.Comment: Accepted for publication in Nanoletters, 8 pages, 3 figure
Metal-Semiconductor Transition in Armchair Carbon Nanotubes by Symmetry Breaking
The electronic band structure of armchair carbon nanotubes may be
considerably modified by potentials with angular dependence. Different angular
modes V_q ~ cos(q*theta) have been studied within a tight-binding scheme. Using
symmetry arguments, we demonstrate a bandgap opening in these metallic
nanotubes when certain selection rules are satisfied for both potential and
nanotube structure. We estimate the bandgap opening as a function of both the
external potential strength and the nanotube radius and suggest an effective
mechanism of metal-semiconductor transition by combination of different forms
of perturbations.Comment: 3 pages, 3 figures, published on AP
Metal-Semiconductor Transition and Fermi Velocity Renormalization in Metallic Carbon Nanotubes
Angular perturbations modify the band structure of armchair (and other
metallic) carbon nanotubes by breaking the tube symmetry and may induce a
metal-semiconductor transition when certain selection rules are satisfied. The
symmetry requirements apply for both the nanotube and the perturbation
potential, as studied within a nonorthogonal -orbital tight-binding
method. Perturbations of two categories are considered: an on-site
electrostatic potential and a lattice deformation which changes the off-site
hopping integrals. Armchair nanotubes are proved to be robust against the
metal-semiconductor transition in second-order perturbation theory due to their
high symmetry, but can develop a nonzero gap by extending the perturbation
series to higher orders or by combining potentials of different types. An
assumption of orthogonality between orbitals is shown to lead to an
accidental electron-hole symmetry and extra selection rules that are weakly
broken in the nonorthogonal theory. These results are further generalized to
metallic nanotubes of arbitrary chirality.Comment: Submitted to Phys. Rev. B, 23 pages, 4 figure
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