F. Bommeli

Optical properties of the A1C60 (A = K, Rb and Cs) linear polymer fullerides

Abstract We have investigated the complete electrodynamic response of the newly discovered alkali fulleride linear polymers A 1 C 60 . We find clear evidence for a metal-insulator phase transition at low temperatures in Rb 1 C 60 and Cs 1 C 60 , while the K compound remains metallic at all temperatures. The possibility of a broken symmetry ground state due to the formation of a spin density wave for the Rb and Cs compounds, as suggested by the magnetic properties, is discussed.

Chapter 9 – Optical Response of Carbon Nanotubes

Publisher Summary This chapter explores the possible metallic nature of CNTs, addressed from the optical point of view. Optical results of oriented CNT films were interpreted within the effective medium Maxwell–Garnett and Bruggeman models. This analysis allowed one to establish the intrinsic metallic nature of the CNTs, with intrinsic parameters in agreement with those inferred by other contactless techniques, as ESR, and theoretical calculations. On the other hand, resistivity measurements on single CNTs give evidence for conductivity up to two orders of magnitude smaller than the one obtained by optical means. In addition, the optical results indicate a remarkable anisotropic conductivity. The findings further enforce the interpretation of dc resistivity measurements being strongly affected by contact effects and intertube hopping. The exceptionally good electron field emitting characteristics of the CNTs make them potentially very attractive for applications in devices such as displays or electron microscopes as shown by W A. de Heer and co-worker. They are used for nanoscale devices. This is the ultimate level of miniaturization in microchip technology. The conductivity gets changed as the active length of the CNT is increased, suggesting that different segments of the CNT exhibit different electronic properties. Carbon with its wide range of sp bond hybridization appears as the key element of a future nanotechnology.

Optical evidence of metal-insulator phase transition in alkali metal doped fullerenes

Abstract We have investigated the complete electrodynamic response of the newly discovered alkali fulleride linear polymers A 1 C 60 . We find clear evidence for a metal-insulator phase transition at low temperatures in Rb 1 C 60 and Cs 1 C 60 , while the K-compound remains metallic at all temperatures. The possibility of a broken symmetry ground state due to the formation of a spin-density-wave (SDW) for the Rb and Cs compound, as suggested by the magnetic properties, is discussed.

Optical properties of the borocarbide superconductors

Abstract We have measured the optical reflectivity of LuNi 2 B 2 C and YNi 2 B 2 C compounds, and have evaluated the optical conductivity both above and below the superconducting transition temperature. The normal state optical properties suggest that these superconductors are almost in the clean limit. Our results below T c give, however, evidence of a superconducting gap signature, and are in agreement with a moderate-to-strong coupling limit of the BCS theory.