High-Tc superconductivity in entirely end-bonded multi-walled carbon nanotubes

We report that entirely end-bonded multi-walled carbon nanotubes (MWNTs) can show superconductivity with the transition temperature Tc as high as 12K that is approximately 40-times larger than those reported in ropes of single-walled nanotubes. We find that emergence of this superconductivity is very sensitive to junction structures of Au electrode/MWNTs. This reveals that only MWNTs with optimal numbers of electrically activated shells, which are realized by the end-bonding, can allow the superconductivity due to inter shell effects.Comment: 5 page

Electronic screening and correlated superconductivity in carbon nanotubes

A theoretical analysis of the superconductivity observed recently in Carbon nanotubes is proposed. We argue that ultra-small (diameter $\sim 0.4 nm$) single wall carbon nanotubes (with transition temperature $T_c\sim 15 ^{o}K$) and entirely end-bonded multi-walled ones ($T_c\sim 12 ^{o}K$) can superconduct by an electronic mechanism, basically the same in both cases. By a Luttinger liquid -like approach, one finds enhanced superconducting correlations due to the strong screening of the long-range part of the Coulomb repulsion. Based on this finding, we perform a detailed analysis on the resulting Hubbard-like model, and calculate transition temperatures of the same order of magnitude as the measured ones.Comment: 6 pages, 1 figure, PACS: 71.10.Pm,74.50.+r,71.20.Tx, to appear in Phys. Rev.

Meissner effect in honeycomb arrays of multi-walled carbon nanotubes

We report Meissner effect for type-II superconductors with a maximum Tc of 19 K, which is the highest value among those in new-carbon related superconductors, found in the honeycomb arrays of multi-walled CNTs (MWNTs). Drastic reduction of ferromagnetic catalyst and efficient growth of MWNTs by deoxidization of catalyst make the finding possible. The weak magnetic anisotropy, superconductive coherence length (- 7 nm), and disappearance of the Meissner effect after dissolving array structure indicate that the graphite structure of an MWNT and those intertube coupling in the honeycomb array are dominant factors for the mechanism.Comment: 6 page

Influence of dimensionality on superconductivity in carbon nanotubes

We investigate the electronic instabilities in carbon nanotubes (CNs), looking for the break-down of the one dimensional Luttinger liquid regime due to the strong screening of the long-range part of the Coulomb repulsion. We show that such a breakdown is realized both in ultra-small single wall CNs and multi wall CNs, while a purely electronic mechanism could explain the superconductivity (SC) observed recently in ultra-small (diameter $\sim 0.4 nm$) single wall CNs ($T_c\sim 15 ^{o}K$) and entirely end-bonded multi-walled ones ($T_c\sim 12 ^{o}K$). We show that both the doping and the screening of long-range part of the electron-electron repulsion, needed to allow the SC phase, are related to the intrinsically 3D nature of the environment where the CNs operate.Comment: 5 pages, 3 figures, PACS: 71.10.Pm,74.50.+r,71.20.Tx, to appear in J. Phys. Cond. Ma

Unconventional Magnetization below 25 K in Nitrogen-doped Diamond provides hints for the existence of Superconductivity and Superparamagnetism

The magnetization of nitrogen-doped single crystalline diamond bulk samples shows unconventional field and temperature hysteresis loops at T ≲ 25 K. The results suggest the existence of superparamagnetic and superconducting regions in samples with nitrogen concentration <200 ppm. Both phases vanish at temperatures above 25 K where the samples show diamagnetic behavior similar to undoped diamond. The observation of superparamagnetism and superconductivity is attributed to the nitrogen doping and to the existence of defective regions. From particle-induced X-ray emission with ppm resolution we rule out that the main observations below 25 K are due to magnetic impurities. We investigated also the magnetic properties of ferromagnetic/high-temperature superconducting oxide bilayers. The magnetization results obtained from those bilayers show remarkable similarities to the ones in nitrogen-doped diamond

Transport Properties in Carbon Nanotubes

This chapter focuses on the general theory of the electron transport properties of carbon nanotubes, yielding an overview of theoretical models. It is organized in five sections describing the results of the research activity performed in electronic/electrical properties modelling. The first section, in addition to describing the scope of the review and providing an introduction to its content, yields as well a general introduction on carbon nanotubes. Sect. 'Electronic Structure of Single-Wall Nanotubes' describes the general theory of the electron transport in carbon nanotubes, starting from the band structure of graphene. Sect. 'Quantum Transport in Carbon Nanotubes' focuses on the quantum transport in carbon nanotubes, including ballistic transport, Coulomb-blockade regime, Luttinger Liquid theory. Sect. 'Results and Experiments' reports results and experimental evidence of the models decribed. Finally, Sect. 'Superconducting transition' addresses the issue of superconductivity transitions in carbon nanotubes

Nanostructures based on cyclic C6

The properties of a new family of carbon structures based on stacked cyclic C6 rings and intercalated cyclic C6 structures: (C6)n and (C6)nMen-1 have been studied theoretically using ab initio DFT (Density Functional Theory). Calculations of the structural, electronic, and vibrational properties of a range of these molecules have been carried out using DFT techniques with the best correspondence to experimental results. The chemical and structural stability of structures based on stacks of cyclic C6 has also been estimated for pure carbon molecules (C6)n and for metal-organic sandwich molecules intercalated with Fe and Ru atoms. These have (C6)nFen-1 and (C6)n Run-1 compositions, respectively These structures are predicted to show a variety of new electronic, vibrational and magnetic properties. Ultra-small diameter tubular molecules are also found to have unique rotational electron states and high atomic orbital pi-sigma hybridization giving rise to a high density of electron states. All phonons in these structures have collinear wave vectors leading to an ultrahigh density of phonon states in dominant modes suggesting that some of these structures may exhibit superconductivity. These properties, as well as a predicted high electron mobility, make these structures promising as components in nanoelectronics. Experiments using femto-second laser pulses for the irradiation of organic liquids suggest that such structures may appear under certain conditions. In particular, a new type of iron carbide has been found in these experiments