Polarons in suspended carbon nanotubes

We prove theoretically the possibility of electric-field controlled polaron formation involving flexural (bending) modes in suspended carbon nanotubes. Upon increasing the field, the ground state of the system with a single extra electron undergoes a first-order phase transition between an extended state and a localized polaron state. For a common experimental setup, the threshold electric field is only of the order of approximately equal 5×10(-2) V/μm.     

Charges on semiconducting nanotubes in polar media: Polarons and excitons

Charge carriers on semiconducting nanotubes immersed in the polar medium such as polar solvents undergo self-trapping into polarons. In the effectively 1d regime polarons are found to have binding energies of approximately 30–35% of the binding energy of excitons. As the thermal dissociation of excitons would occur into polaron pairs, the thermal ionization energy of excitons is substantially reduced, which is expected to lead to enhanced separation of charges.     

Dominoes in carbon nanotubes

We demonstrate by molecular dynamics simulations that the domino process can be developed in single-walled carbon nanotubes (SWCNTs). Once a section of a SWCNT with an appropriate diameter (>3.5 nm) is collapsed, the successive collapse of the neighboring portions can generate a domino wave along the longitudinal direction of the tube. The wave is driven by van der Waals potential energy and its natural speed can be up to 1 km/s. Molecules inside the SWCNT can be accelerated by the domino wave and finally shot out. The finding shows for the first time that a SWCNT can be an energy supplier, which provides opportunities for designing new concept (domino-driven) nanoelectromechanical system devices.     

Phonons in carbon nanotubes

A broad review of the unusual one-dimensional properties of phonons in carbon nanotubes is presented, including phonons in isolated nanotubes and in crystalline arrays of nanotubes in nanotube bundles. The main technique for probing the phonon spectra has been Raman spectroscopy and the many unique and unusual features of the Raman spectra of carbon nanotubes are reviewed. Also included is a brief review of the thermal properties of carbon nanotubes in relation to their unusual phonon dispersion relations and density of states.     

Filling carbon nanotubes

Received: 2 March 1998     

Super-slippery carbon nanotubes

The friction between the walls of multi-wall carbon nanotubes is shown to be extremely low in general, with important details related to the specific choice of the walls. This is governed by a simple expression revealing that the phenomenon is a profound consequence of the specific symmetry breaking: super-slippery sliding of the incommensurate walls is a Goldstone mode. Three universal principles of tribology, offering a recipe for lubricant selection are emphasized. Received 8 August 2001     

Polarons in thet-J model

A convenient form of the Peierls-Hubbard Hamiltonian is obtained for the case when the Hubbard repulsion is the largest energy parameter. It allows to consider in the spin-wave approximation the properties of the one-hole low-lying excitations of a 2d lattice. For the parameters approximately corresponding to La₂CuO₄ it is shown that the hole polarons in the CuO₂ planes of lightly doped samples are of large size with a solitonlike-shaped highly asymmetric wave function oriented along the diagonals of the planes or of small size depending on the value of the electron-phonon coupling. In both cases the cooperative effect of the electron-phonon and electron-magnon interactions leads to a large effective mass and to hopping transport of the excitations, with preferential jumps along the diagonals in the former case and rotationally symmetric in the latter. For hoping matrix elements which are small in comparison with a phonon quantum the competition between the interactions leads to the decrease of the total spin in the ground state with increasing electron-phonon coupling.     

Spin-polarized transport in carbon nanotubes

We present transport measurements of ferromagnetically contacted carbon nanotubes. In both single- and multi-walled nanotube devices, a spin valve effect is observed due to spin-polarized transport. In one single-walled nanotube device, the spin-valve effect is suppressed as the influence of Coulomb charging is observed at around 10 K. To help understand the interplay between the Coulomb charging and the spin-polarized transport we investigated the temperature dependence of the carbon nanotube magnetoresistance.     

Correlated transport in carbon nanotubes

The low-energy theory for single-wall armchair carbon nanotubes including Coulomb interactions is given. It describes two fermion chains without interchain hopping but coupled in a specific way by the interaction. The strong-coupling properties are studied by bosonization, and the consequences for experiments on single armchair nanotubes are discussed.     

Charge pumping in carbon nanotubes

We demonstrate charge pumping in semiconducting carbon nanotubes by a traveling potential wave. From the observation of pumping in the nanotube insulating state we deduce that transport occurs by packets of charge being carried along by the wave. By tuning the potential of a side gate, transport of either electron or hole packets can be realized. Prospects for the realization of nanotube based single-electron pumps are discussed.     

Dissipative solitons in carbon nanotubes

The possibility of analogs of dissipative solitons occurring in arrays of carbon nanotubes under the action of a high-frequency external uniform electric field on the array has been established theoretically. The electromagnetic field has been considered in terms of the Maxwell equations, and the conduction electrons in carbon nanotubes have been described by the Boltzmann kinetic equation in the relaxation-time approximation. The external ac electric field serves for energy pumping of the electronic subsystem, whereas a finite relaxation time leads to energy dissipation. The generation of a periodic sequence of electromagnetic pulses has been revealed. This sequence can be used for producing terahertz frequencies.     

Quantum entanglement in carbon nanotubes

With the surge of research in quantum information, the issue of producing entangled states has gained prominence. Here, we show that judiciously bringing together two systems of strongly interacting electrons with vastly differing ground states-the gapped BCS superconductor and the Luttinger liquid-can result in quantum entanglement. We propose three sets of measurements involving single-walled metallic carbon nanotubes which have been shown to exhibit Luttinger liquid physics, to test our claim and as nanoscience experiments of interest in and of themselves.     

Biexciton stability in carbon nanotubes

We have applied the quantum Monte Carlo method and tight-binding modeling to calculate the binding energy of biexcitons in semiconductor carbon nanotubes for a wide range of diameters and chiralities. For typical nanotube diameters we find that biexciton binding energies are much larger than previously predicted from variational methods, which easily brings the biexciton binding energy above the room temperature threshold.     

Endohedral impurities in carbon nanotubes

A generalization of the Anderson model that includes pseudo-Jahn-Teller impurity coupling is proposed to describe distortions of an endohedral impurity in a carbon nanotube. Within mean-field theory, spontaneous axial symmetry breaking is found when the vibronic coupling strength g exceeds a critical value. The effective potential is found to have O(2) symmetry, in agreement with numerical calculations. For metallic zigzag nanotubes endohedrally doped with transition metals in the dilute limit, the low-energy properties of the system may display two-channel Kondo behavior; however, strong vibronic coupling is seen to exponentially suppress the Kondo energy scale.     

Dissipative solitons in carbon nanotubes

The theoretical possibility of the existence of dissipative solitons in an array of carbon nanotubes when they are subjected to external uniform high-frequency electric field is discussed. An external alternating field is used for energy pumping of the electron subsystem, while a finite relaxation time leads to energy dissipation. The generation of a periodic sequence of electromagnetic pulses is revealed.     

Quantum transport in carbon nanotubes

A survey will be given on selected experiments showing evidence of quantum transport in carbon nanotubes. The phenomena involve electron confinement, single electron effects and Coulomb–Blockade, Kondo-physics, conductance quantisation, Aharonov–Bohm effect, phase breaking in ballistic transport, and magnetochiral anisotropy.     

Quantum-dot transport in carbon nanotubes

Transport measurements on a bundle of single-walled carbon nanotubes have been made below 4.2 K as a function of side gate and source–drain bias voltage. The transport of an individual nanotube is described by the Coulomb blockade effect. The zero-dimensional quantum states of the nanotube become clear for measurements of large bias voltage. In addition, we present preliminary results of microwave application to the SWNT dot, and the results can be qualitatively explained by classical coupling to the dot.