Probing the electronic properties of single-walled carbon nanotubes with resonant and non-resonant microwave absorption

Microwave absorption (MA) is applied to study the electromagnetic properties of bulk samples of single-walled carbon nanotubes (SWNT). Using resonant MA (electron paramagnetic resonance) and also its non-resonant variant (cavity perturbation) it was possible to reveal different electronic phases of SWNT. Besides the existence of doped semiconducting nanotubes with an activation energy of 67 meV, also small-bandgap semiconducting tubes with a gap-energy of 7 meV could be detected. Additionally, at temperatures below 12 K an unconventional loss mechanism occurs. The properties of this non-linear absorptive state give evidence for the occurrence of superconducting domains in the samples.