Multi-Frequency EPR and DC Conductivity of Itinerant Spins in Single-Wall Carbon Nanotubes
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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.
We are grateful to K. Hata (National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan), who provided us with SWNT samples. Financial support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged. The National High Magnetic Field Laboratory (NHMFL) is operated by the National Science Foundation (DMR-08). Experiments at the NHFML (Tallahassee) were supported by a visiting professor fellowship to K.P.D.
- 5.B. Corzilius, K.-P. Dinse, K. Hata, M. Haluška, V. Skákalová, S. Roth, Phys. Stat. Sol. (b) 245, 2251 (2008)Google Scholar