Superconductivity in carbon nanotube ropes

TL;DR

This paper explores the emergence of superconductivity in ropes of carbon nanotubes, highlighting how intertube interactions and phonon-mediated attraction can lead to a superconducting phase in large metallic nanotube bundles.

Contribution

It demonstrates that large bundles of metallic nanotubes can develop superconductivity due to reduced Coulomb repulsion and phonon exchange, emphasizing the role of pair tunneling between tubes.

Findings

Superconductivity is favored in ropes with about 100 or more metallic nanotubes.

Long-range Coulomb interactions are effectively reduced in large nanotube bundles.

Pair tunneling between nanotubes is more probable than single-electron tunneling, facilitating superconductivity.

Abstract

We investigate the conditions in which superconductivity may develop in ropes of carbon nanotubes. It is shown that the interaction among a large number of metallic nanotubes favors the appearance of a metallic phase in the ropes, intermediate between respective phases with spin-density-wave and superconducting correlations. These arise in samples with about 100 metallic nanotubes or more, where the long-range Coulomb interaction is very effectively reduced and it may be overcome by the attractive interaction from the exchange of optical phonons within each nanotube. We estimate that the probability for the tunneling of Cooper pairs between neighboring nanotubes is much higher than that for single electrons in a disordered rope. The effect of pair hopping is therefore what establishes the intertube coherence, and the tunneling amplitude of the Cooper pairs dictates the scale of the transition to the superconducting state.