Insulating and conducting phases ofRbC60

Abstract

Optical measurements were performed on thin films of RbxC60, identified by X-ray diffraction as mostly x = 1 material. The samples were subjected to various heat treatments, including quenching and slow cooling from 400K. The dramatic increase in the transmission of the quenched samples, and the relaxation towards the transmission observed in slow cooled samples provides direct evidence for the existence of a metastable insulating phase. Slow cooling results in a phase transition between two electrically conducting phases.

Optical spectroscopy on monomeric and polymeric 1:1 fulleride salts

“…If the distance between fulleride ions gets shorter, the modes should harden in absence of other perturbations; electron-phonon interaction, on the other hand, causes softening whose magnitude depends on the strength of the coupling. As shown both experimentally [4,5] and theoretically [6], the highestfrequency mode has a much larger electron-phonon coupling constant than the 1183 cm -1 mode. Therefore, the former is indicative of the coupling, while the latter reflects the changes in lattice constant.…”

“…There is growing evidence for an orthogonal phase (ortho-I) consisting of covalently bound polymers [1,2] and another one (ortho-II) of dimers [3]. Vibrational spectroscopy has been used to identify the valence state of anions in C60 salts [4,5] and it was shown early on that electron-phonon interactions play a significant role in the infrared properties of the salts [6]. In this study, we compare the infrared spectra of different phases of RbC60 to (Ph4)2C60I, a charge transfer salt containing C60 monoanions.…”

Electronic surface reconstruction and correlation in the fcc and dimer phases ofRbC60

“…24 While NMR ͑Ref. 18͒ and electron spin resonance 13 investigations on the fcc phase revealed a high degree of localization of the unpaired electrons on individual C 60 molecules, optical conductivity measurements 25 found a metallic character, pointing to the correlated nature of the fcc phase. Like solid ͑C 59 N͒ 2 , the metastable dimer phase is insulating and diamagnetic, which derives from the fact that one electron per cage participates in the dimer bond and the nondegenerate orbital close to the Fermi level is totally filled.…”

Development of Conductive Organic Molecular Assemblies: Organic Metals, Superconductors, and Exotic Functional Materials

“…100 C, AC 60 (A ¼ K, Rb, and Cs) salts adopt a fcc rocksalt structure 1048 showing a Curie-like magnetic behavior, 1017 although the metallic behavior was observed for conductivity measurements. 1049 Upon slow cooling, the salts undergo a structural transition from cubic to orthorhombic symmetry at ca. 350 K, leading to the air-stable polymer phase consisting of [2 þ 2] cycloadduct linear chains.…”