Periodic steps in the resistance vs. temperature characteristics of doped graphite and graphene: evidence of superconductivity?

TL;DR

This study reports periodic resistance steps in doped graphite and graphene, suggesting possible superconductivity, with some evidence of vortex pinning, but lacking direct superconducting gap measurements or Meissner effect confirmation.

Contribution

It provides experimental evidence of resistance steps in doped layered carbon materials, indicating potential superconductivity with vortex pinning phenomena, a novel observation in this context.

Findings

Resistance steps observed at specific temperatures

Magnetic field quenching affects the steps

Sharpened steps after ion implantation

Abstract

We have observed periodically repeated steps in the resistance vs. temperature characteristics of doped Highly Oriented Pyrolytic Graphite and exfoliated doped multi-layer graphene. The observations consist of a series of regularly spaced steps in the resistance vs. temperature curves. The lowest step is observed at a temperature of from 50 to 60 K. Additional steps are observed at multiples of that basic temperature with the highest step temperature being at approximately 270 K. Quenching by a modest applied magnetic field has been observed. The sizes and widths of the observed steps appear to vary and may be related to some sort of aggregation reminiscent of flux vortex pinning. An additional argon ion implantation at reduced energy was done to see if additional defects in the material would yield additional structure. This was observed to yield much sharper resistance steps at temperatures in excess of 200 K in thin exfoliated peels from the implanted surface of the sample and would support the possibility of the steps being related to pancake vortex pinning in a layered superconductor. Unfortunately, as yet, there has been no direct measurement of either the superconducting energy gap nor has a definitive Meissner effect been observed.