Nano Lett. (2018)

Superconductivity in reduced dimensions is prone to effects not present in bulk superconductors. Somewhat surprisingly, Feng Qin et al. now show that the critical temperature of superconducting WS2 nanotubes decreases with the diameter.

The researchers intercalated potassium in individual multiwall WS2 nanotubes to make them superconducting and determined the critical temperature of the nanotubes. They also measured the conductance through the tubes as a function of magnetic field. If the field is applied parallel to the tube, a supercurrent flows along the tube’s circumference and produces quantum interference. The interference creates oscillations in the resistance with increasing magnetic field and enables a determination of the effective tube diameter. Although the critical temperature appears to be independent of the wall thickness, it scales linearly with the inverse diameter of the tube. This result comes as a surprise; for carbon nanotubes, theory had predicted an increasing electron–phonon coupling with shrinking diameter, which should augment the critical temperature. Qin et al. now speculate that the observed decrease in critical temperature for WS2 is linked to lattice distortions in the tubes, which could yield unconventional electron–phonon interactions.