44 research outputs found
``X-Ray Edge'' Singularities in Nanotubes and Quantum Wires with Multiple Subbands
Band theory predicts an inverse square root van Hove singularity in the
tunneling density of states at the minimum energy of an unoccupied subband in a
one-dimensional quantum wire. With interactions, an orthogonality catastrophe
analogous to the x-ray edge effect for core levels in a metal strongly reduces
this singularity by a power B of the energy above threshold, with B
approximately 0.3 for typical carbon nanotubes. Despite the anomalous tunneling
characteristic, good quasiparticles corresponding to the unoccupied subband
states do exist.Comment: 4 page
Random walks on finite lattice tubes
Exact results are obtained for random walks on finite lattice tubes with a
single source and absorbing lattice sites at the ends. Explicit formulae are
derived for the absorption probabilities at the ends and for the expectations
that a random walk will visit a particular lattice site before being absorbed.
Results are obtained for lattice tubes of arbitrary size and each of the
regular lattice types; square, triangular and honeycomb. The results include an
adjustable parameter to model the effects of strain, such as surface curvature,
on the surface diffusion. Results for the triangular lattice tubes and the
honeycomb lattice tubes model diffusion of adatoms on single walled zig-zag
carbon nano-tubes with open ends.Comment: 22 pages, 4 figure
Van Hove Singularities in disordered multichannel quantum wires and nanotubes
We present a theory for the van Hove singularity (VHS) in the tunneling
density of states (TDOS) of disordered multichannel quantum wires, in
particular multi-wall carbon nanotubes. We assume close-by gates which screen
off electron-electron interactions. Diagrammatic perturbation theory within a
non-crossing approximation yields analytical expressions governing the
disorder-induced broadening and shift of VHS's as new subbands are opened. This
problem is nontrivial because the (lowest-order) Born approximation breaks down
close to the VHS. Interestingly, compared to the bulk case, the boundary TDOS
shows drastically altered VHS, even in the clean limit.Comment: 4 pages, 2 figures, accepted with revisions in PR
Charge Screening Effect in Metallic Carbon Nanotubes
Charge screening effect in metallic carbon nanotubes is investigated in a
model including the one-dimensional long-range Coulomb interaction. It is
pointed out that an external charge which is being fixed spatially is screened
by internal electrons so that the resulting object becomes electrically
neutral. We found that the screening length is given by about the diameter of a
nanotube.Comment: 11 pages, 6 figure
Superconductivity in carbon nanotube ropes
We investigate the conditions in which superconductivity may develop in ropes
of carbon nanotubes. It is shown that the interaction among a large number of
metallic nanotubes favors the appearance of a metallic phase in the ropes,
intermediate between respective phases with spin-density-wave and
superconducting correlations. These arise in samples with about 100 metallic
nanotubes or more, where the long-range Coulomb interaction is very effectively
reduced and it may be overcome by the attractive interaction from the exchange
of optical phonons within each nanotube. We estimate that the probability for
the tunneling of Cooper pairs between neighboring nanotubes is much higher than
that for single electrons in a disordered rope. The effect of pair hopping is
therefore what establishes the intertube coherence, and the tunneling amplitude
of the Cooper pairs dictates the scale of the transition to the superconducting
state.Comment: 12 page
Vacuum structure of Toroidal Carbon Nanotubes
Low energy excitations in carbon nanotubes can be described by an effective
field theory of two components spinor. It is pointed out that the chiral
anomaly in 1+1 dimensions should be observed in a metallic toroidal carbon
nanotube on a planar geometry with varying magnetic field. We propose an
experimental setup for studying this quantum effect. We also analyze the vacuum
structure of the metallic toroidal carbon nanotube including the Coulomb
interactions and discuss some effects of external charges on the vacuum.Comment: 10 pages, 11 figure
Theoretical STM signatures and transport properties of native defects in carbon nanotubes
Article on theoretical STM signatures and transport properties of native defects in carbon nanotubes