SWNT probed by multi-frequency EPR and nonresonant microwave absorption

• Published in: Physica Status Solidi (b) 2008-10, Vol.245 (10), p.2251-2254
• Main Authors: Corzilius, B., Dinse, K.-P., Hata, K., Haluška, M., Skákalová, V., Roth, S.
• Format: Article
• Language: English
• Subjects: 72.80.Rj; 73.63.Fg; 74.70.Wz; 74.81.Fa; 76.30.Da; 76.30.Pk; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron paramagnetic resonance and relaxation; Exact sciences and technology; Magnetic resonances and relaxations in condensed matter, mössbauer effect; Mesoscopic and nanoscale systems; Microwave and radio-frequency interactions (excluding resonances); Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other interactions of matter with particles and radiation; Physics; Superconducting films and low-dimensional structures; Superconductivity
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.200879574

In addition to g = 2.00 signals seen frequently in EPR spectra of SWNT, signals at g = 2.07 of SWNT prepared by CVD were detected, exhibiting a Pauli susceptibility temperature dependence. This Pauli magnetism in combination with the large g shift is taken as evidence that these signals originate from itinerant electrons of metallic nanotubes. At temperatures below 150 K, a dominant narrow signal develops at g = 2.00. By applying multifrequency EPR up to 319 GHz, its inhomogeneous nature was confirmed. This signal is assigned to defects of the carbon network of the tubes. Comparing room temperature EPR spectra of CVD and arc‐grown SWNT, we found a much lower concentration of metallic tubes in arc material. No g = 2.07 signals of itinerant spins could be observed, which might be also caused by the high amount of residing catalyst. A drastic increase in nonresonant microwave absorption is observed below 10 K for both types of samples, if a threshold microwave power level is passed. In the same temperature range a drop in EPR intensity is also detected. These observations are taken as evidence for a transition into a superconducting phase of part of the sample. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)