Peierls transition with acoustic phonons and solitwistons in carbon nanotubes

Twist instability in strongly correlated carbon nanotubes

We show that strong Luttinger correlations of the electron liquid in armchair carbon nanotubes significantly enhance the onset temperature of the putative twist Peierls instability and lead to its 1/R3 dependence on the tube radius. Depending on the values of the coupling constants the umklapp processes can either assist or compete with the twist instability. In the case of a competition the umklapp processes win in wide tubes. In narrow tubes the outcome of the competition depends on the relative strength of the e-e and e-ph backscattering. Our estimates show that the twist instability may be realized in freestanding (5,5) tubes.

Excitons and Peierls distortion in conjugated carbon nanotubes

We investigate coupled excitonic and vibrational effects in carbon nanotubes using a time-dependent Hartree-Fock approach. The results reveal intricate details of excited-state dynamics. In the ground state, spontaneous uneven distribution of the pi electrons over the bonds (i.e., Peierls dimerization) is observed throughout the entire nanotube, particularly in large-radius CNTs. However, we demonstrate that vibrational relaxation following photoexcitations leads to substantial local distortion of the tube surface, overriding the Peierls dimerization. This mutually affects the electronic system, resulting in localized states (self-trapped excitons). These phenomena critically control photoinduced dynamics and charge transport in nanotube materials.

Room temperature peierls distortion in small diameter nanotubes

By means of ab initio simulations, we investigate the phonon band structure and electron-phonon coupling in small 4-A diameter nanotubes. We show that both the C(5,0) and C(3,3) tubes undergo above room temperature a Peierls transition mediated by an acoustical long wavelength and an optical q=2k(F) phonon, respectively. In the armchair geometry, we verify that the electron-phonon coupling parameter lambda originates mainly from phonons at q=2k(F) and is strongly enhanced when the diameter decreases. These results question the origin of superconductivity in small diameter nanotubes.

Phonon softening in metallic nanotubes by a Peierls-like mechanism

The radial dependency of the vibrational frequencies of single-wall carbon nanotubes in the G band (1500-1600 cm(-1)) is studied by density functional theory. In metallic nanotubes, a mode with A1 symmetry is found to be significantly softer than the corresponding mode in insulating tubes or graphite. The mechanism that leads to the mode softening is explored. It is reminiscent of the driving force inducing Peierls distortions. At ambient temperature, the energy gained by opening the gap is, however, not sufficient for a static lattice distortion. Instead the corresponding vibrational frequency is lowered.