Magnetic evidence for hot superconductivity in multi-walled carbon nanotubes

TL;DR

This study presents magnetic evidence of superconductivity in multi-walled carbon nanotubes at temperatures exceeding 500 K, including a transition at about 1200 K, suggesting potential for high-temperature superconducting applications.

Contribution

The paper provides the first magnetic measurements indicating superconductivity above room temperature in multi-walled carbon nanotubes, with clear transitions and exclusion of magnetic impurities as causes.

Findings

Superconducting transition between 533 K and 700 K.

Another transition observed at about 1200 K.

Diamagnetic Meissner fractions of 2% and 14%.

Abstract

We report magnetic measurements up to 1200 K on three different multi-walled carbon nanotube mat samples using Quantum Design vibrating sample magnetometers. Three different samples prepared from arc discharge or chemical vapor deposition contain magnetic impurities ranging from about 100 ppm to about 1.5%. Our precise magnetic data clearly show two superconducting transitions, one at temperatures between 533 K and 700 K, and another at about 1200 K. The first transition temperature T_cJ, which coincides with the transition temperature seen in the resistance data, depends very strongly on the magnetic field, as expected from the onset of intergrain Josephson coupling in granular superconductors. The strong field dependence of T_cJ also excludes magnetic contaminants as the origin of the first transition. We also present direct and inferred diamagnetic Meissner fractions of 2 and 14%, respectively. The present results provide compelling evidence for superconductivity well above room temperature in multi-walled carbon nanotubes.