Helium atoms are believed to be strongly bound within the interstitial channels in bundles of carbon nanotubes. In a recent paper [F. Ancilotto et al., Phys. Rev. B 70, 165422 (2004)] inhomogeneity in the size distribution of nanotube radii was shown to make a system of
4He atoms in such an environment effectively a four-dimensional Bose gas, thus permitting a Bose-Einstein condensation (BEC) of the adsorbed atoms into the minimum energy state. This surprising result was obtained for a model of noninteracting atoms in a continuum distribution of (virtually) infinite interstitial channels. Here we investigate how the singular thermal properties of the ideal system and the occurrence of BEC are affected by a more realistic modeling of a bundle of nanotubes where (i) the number of nanotubes is finite and where (ii)
4He atoms adsorbed within the same interstitial channel interact among themselves. Also in this case we observe an anomalous heat capacity close to the ideal condensation temperature, suggesting the persistence of the condensation transition for interacting
4He atoms, which might be experimentally observed.
Ultrafast relaxation dynamics of photogenerated carriers in nanostructure based saturable absorber (SA) are investigated using a degenerate cross-polarized pump–probe experiment at 1.55 µm operating wavelength. Single-walled carbon nanotubes (SWNT) encased in micelles are studied and compared to bundled ones as well as to iron doped InGaAs/InP multiple quantum wells (MQW). SA parameters for all optical signal regeneration (AOSR) are extracted from the normalized differential transmission. Although all samples show the same order of recombination time, SWNT in micelles present a much higher contrast ratio associated to a lower level of saturation fluence as compared to their bundled and MQW counterparts.
Using a carbon nanotube (CNT) bundle tip as a field emitter, we have observed both Coulomb blockade and interference fringes in consecutive measurements. When Coulomb blockade is observed, decoherence of the electron wave occurs. This was observed using a double-tunnel junction consisting of a CNT tip and a CNT sample. When the CNT sample was projected onto a screen by an electron wave from the CNT tip, interference fringes were observed. This shows that the electron is first observed at the central electrode as a Coulomb blockade, next it is observed at the CNT sample as current when the electron leaves from the central electrode (the CNT tip) and finally observed as fringes passing through the CNT sample. These results show that the system's wave function cannot be written as a direct product of independent substates.