Multi-Frequency EPR and DC Conductivity of Itinerant Spins in Single-Wall Carbon Nanotubes

Abstract

Sealed, deoxygenated single-wall carbon nanotubes show two characteristic electron paramagnetic resonance (EPR) signals at g = 2.07 and g = 2.00 in the temperature range from 300 to 50 K. Reversible interconversion between both components was observed. The large g-shift and the temperature dependence of the EPR susceptibility of the g = 2.07 signal indicate that this signal can be attributed to itinerant spins. At low temperatures only the g = 2.00 signal remained, which could be further characterized using microwave frequencies up to 320 GHz. The direct current conductivity of a partially aligned sample was also measured. The room temperature value was estimated as 0.7 (Ωcm)−1. The observed temperature dependence can be described by assuming temperature-activated hopping in a small-gap semiconductor with an activation energy of 3.5 meV, similar to the characteristics of the previously measured 9.4 GHz microwave conductivity.