Magnetic order and superconductivity observed in bundles of Double-Wall Carbon Nanotubes

TL;DR

This study reveals magnetic order and potential superconductivity in double-wall carbon nanotube bundles through magnetotransport measurements, showing negative and positive magnetoresistance behaviors and temperature-dependent phenomena.

Contribution

It provides the first evidence of magnetic order and possible superconductivity in DWCNT bundles, combining transport and magnetization data.

Findings

Magnetoresistance is negative above 15 K, indicating magnetic order.

At low temperatures, positive magnetoresistance and hysteresis suggest superconductivity.

Resistance behavior transitions from ohmic to non-ohmic with temperature.

Abstract

The magnetotransport properties were studied in hundreds of micrometer length double-wall carbon nanotubes (DWCNT) bundles. Above 15 K the resistance shows an ohmic behavior and its temperature dependence is well described using the variable-range hopping for one-dimensional system. The magnetoresistance is negative and can be explained using an empirical model based on spin-scattering processes indicating the existence of magnetic order up to room temperature. At temperatures between 2 K and 15 K the resistance is non-ohmic and the current-voltage characteristics reveal the appearance of a potential, which can be well described by a fluctuation-induced tunneling conduction model. In this low temperature range and at low enough input current, a positive magnetoresistance appears - in addition to the negative one - with an extraordinary hysteresis in field and vanishes at $T \sim 15 $K, suggesting the existence of a superconducting state. Magnetization results partially support the existence of both phenomena in the DWCNT bundles.