1,257 research outputs found
Effects of magnetic field and disorder on electronic properties of Carbon Nanotubes
Electronic properties of metallic and semiconducting carbon nanotubes are
investigated in presence of magnetic field perpendicular to the CN-axis, and
disorder introduced through energy site randomness. The magnetic field field is
shown to induce a metal-insulator transition (MIT) in absence of disorder, and
surprisingly disorder does not affect significantly the MIT. These results may
find confirmation through tunneling experimentsComment: 4 pages, 6 figures. Phys. Rev. B (in press
Spin configurations of carbon nanotube in a nonuniform external potential
We study, theoretically, the ground state spin of a carbon nanotube in the
presence of an external potential. We find that when the external potential is
applied to a part of the nanotube, its variation changes the single electron
spectrum significantly. This, in combination with Coulomb repulsion and the
symmetry properties of a finite length armchair nanotube induces spin flips in
the ground state when the external potential is varied. We discuss the possible
application of our theory to recent measurements of Coulomb blocked peaks and
their dependence on a weak magnetic field in armchair carbon nanotubes.Comment: RevTeX, 5 pages + two figure
Universality of electron correlations in conducting carbon nanotubes
Effective low-energy Hamiltonian of interacting electrons in conducting
single-wall carbon nanotubes with arbitrary chirality is derived from the
microscopic lattice model. The parameters of the Hamiltonian show very weak
dependence on the chiral angle, which makes the low energy properties of
conducting chiral nanotubes universal. The strongest Mott-like electron
instability at half filling is investigated within the self-consistent harmonic
approximation. The energy gaps occur in all modes of elementary excitations and
estimate at eV.Comment: 4 pages, 2 figure
Luttinger liquid behavior in multi-wall carbon nanotubes
The low-energy theory for multi-wall carbon nanotubes including the
long-ranged Coulomb interactions, internal screening effects, and
single-electron hopping between graphite shells is derived and analyzed by
bosonization methods. Characteristic Luttinger liquid power laws are found for
the tunneling density of states, with exponents approaching their Fermi liquid
value only very slowly as the number of conducting shells increases. With minor
modifications, the same conclusions apply to transport in ropes of single-wall
nanotubes.Comment: 4 pages Revte
Strong correlation effects in single-wall carbon nanotubes
We present an overview of strong correlations in single-wall carbon
nanotubes, and an introduction to the techniques used to study them
theoretically. We concentrate on zigzag nanotubes, although universality
dictates that much ofthe theory can also be applied to armchair or chiral
nanotubes. We show how interaction effects lead to exotic low energy properties
and discuss future directions for studies on correlation effects in nanotubes
Subband population in a single-wall carbon nanotube diode
We observe current rectification in a molecular diode consisting of a
semiconducting single-wall carbon nanotube and an impurity. One half of the
nanotube has no impurity, and it has a current-voltage (I-V) charcteristic of a
typical semiconducting nanotube. The other half of the nanotube has the
impurity on it, and its I-V characteristic is that of a diode. Current in the
nanotube diode is carried by holes transported through the molecule's
one-dimensional subbands. At 77 Kelvin we observe a step-wise increase in the
current through the diode as a function of gate voltage, showing that we can
control the number of occupied one-dimensional subbands through electrostatic
doping.Comment: to appear in Physical Review Letters. 4 pages & 3 figure
Role of Single Defects in Electronic Transport through Carbon Nanotube Field-Effect Transistors
The influence of defects on electron transport in single-wall carbon nanotube
field effect transistors (CNFETs) is probed by combined scanning gate
microscopy (SGM) and scanning impedance microscopy (SIM). SGM reveals a
localized field effect at discrete defects along the CNFET length. The
depletion surface potential of individual defects is quantified from the
SGM-imaged radius of the defect as a function of tip bias voltage. This
provides a measure of the Fermi level at the defect with zero tip voltage,
which is as small as 20 meV for the strongest defects. The effect of defects on
transport is probed by SIM as a function of backgate and tip-gate voltage. When
the backgate voltage is set so the CNFET is "on" (conducting), SIM reveals a
uniform potential drop along its length, consistent with diffusive transport.
In contrast, when the CNFET is "off", potential steps develop at the position
of depleted defects. Finally, high-resolution imaging of a second set of weak
defects is achieved in a new "tip-gated" SIM mode.Comment: to appear in Physical Review Letter
Exciton binding energies in carbon nanotubes from two-photon photoluminescence
One- and two-photon luminescence excitation spectroscopy showed a series of
distinct excitonic states in single-walled carbon nanotubes. The energy
splitting between one- and two-photon-active exciton states of different
wavefunction symmetry is the fingerprint of excitonic interactions in carbon
nanotubes. We determine exciton binding energies of 0.3-0.4 eV for different
nanotubes with diameters between 0.7 and 0.9 nm. Our results, which are
supported by ab-initio calculations of the linear and non-linear optical
spectra, prove that the elementary optical excitations of carbon nanotubes are
strongly Coulomb-correlated, quasi-one dimensionally confined electron-hole
pairs, stable even at room temperature. This alters our microscopic
understanding of both the electronic structure and the Coulomb interactions in
carbon nanotubes, and has direct impact on the optical and transport properties
of novel nanotube devices.Comment: 5 pages, 4 figure
Autoactivation of human blood coagulation factor XII on Dextran derivatives of different molecular weight
Electronic Properties of Armchair Carbon Nanotubes : Bosonization Approach
The phase Hamiltonian of armchair carbon nanotubes at half-filling and away
from it is derived from the microscopic lattice model by taking the long range
Coulomb interaction into account. We investigate the low energy properties of
the system using the renormalization group method. At half-filling, the ground
state is a Mott insulator with spin gap, in which the bound states of electrons
at different atomic sublattices are formed. The difference from the recent
results [Phys. Rev. Lett. 79, 5082 (1997)] away half-filling is clarified.Comment: 4 pages, 1 figure, Revte
- …