Electron spin resonance study of the polymeric phase ofNa2RbC60

The structural and electronic properties of the polymeric phase of ${\mathrm{Na}}_2{\mathrm{RbC}}_{60}$ which comprises of C-C bridged $C_{60}^{3-}$ chains have been studied between 410 and 4 K with the electron spin resonance (ESR) technique. On cooling, the polymeric phase starts growing below ∼250 K. Its fraction reaches a maximum at ∼190 K, where around 55% of the monomeric cubic phase have transformed to the polymer. The temperature dependence of the ESR susceptibility suggests that the ${\mathrm{Na}}_2{\mathrm{RbC}}_{60}$ polymer is conducting down to 4 K. The ESR results exclude the possibility of the existence of a ground-state instability and the formation of either a spin-density-wave (SDW) or a charge-density-wave (CDW) state.