Superconducting Mechanism in multi-walled Carbon Nanotubes

Recently Japanese group led by Haruyama [1] reported the significant enhancement of superconductivity, i.e., Tc=12K, in end-bonded Multi-walled Carbon Nanotubes. We can explain the enhancement by the electron confinement in the lateral direction, i.e., between the inner and outer cylinders, because electron density correlation enhances the phonon-mediated superconductivity. In other words, superconductivity in the (multi-walled) Carbon Nanotubes is due to the electron-phonon interaction and Tc is enhanced due to the density correlation caused by the confinement. First, we use simple concentric rings to estimate the Tc enhancement using the BCS theory. Next, we use the tight-binding model to calculate the Tc increase more accurately. In this context, this experimental result is very similar to the enhancement of Tc=15K in 4 angstrom single-walled Carbon Nanotubes by Tang et al. [2]. [1] I. Takesue et al., Phys. Rev. Lett., Vol. 96, 057001 (2006). [2] Z. K. Tang et al., Science, Vol. 292, 2462 (2001).