Anomalous Metallic State Coexisting with the Charge Density Wave in Rb3Cu8S6Studied by NMR and Spin Echo Double Resonance (SEDOR)

Abstract

The metallic state below the charge density wave (CDW) transition temperature of Rb 3 Cu 8 S 6 has been studied by NMR and spin echo double resonance (SEDOR). This compound is known to show metallic characteristics below T c2 =55 K, although the CDW already sets in at T c1 =120 K. It has been found that some of the Cu-NMR lines start to spread out below T c1 , and remain broadened even below T c2 . In order to gain further insight into the state below T c2 , we applied SEDOR to the broadened Cu-lines below T c2 . A double-horned shape characteristic of CDW states was found in one of the SEDOR spectra, which is considered to be a manifestation of the presence of the CDW even below T c2 . The SEDOR reduction is attributed to a kind of motion in the CDW chains. On the other hand, the spin-lattice relaxation rate at the Rb sites was found to decrease rapidly below T c2 , implying that the Rb sites are not inert, but play important roles in this metallic state. As a possible mechanism for this anomalous metallic state, the spinless (charged)-soliton conduction on the CDW chains is discussed.