Electronic properties of ortho-polymer A1C60 (A = K, Rb) and related phases

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C₆₀. Its singular structural, magnetic and electrical properties greatly enhanced the study of the AC₆₀ phases (A = Rb, K and \chem{Cs}). We report our continuous wave (cw) ESR results on the structural phase transformations, phase instabilities and the related kinetics of K₁C₆₀. We quantitatively explain the origin of the difference between Rb₁C₆₀ and K₁C₆₀ phase diagrams. The stability of OP-Rb₁C₆₀ together with the narrowness of its homogenous cw-ESR linewidth in the temperature range \rangeunit{16}{100}{K} allow to perform pulsed ESR experiments. Pulsed ESR experiments measure precisely both the electronic spin-spin (T_2) and spin-lattice (T_1) relaxation times. Above \valunit{40}{K}, the equality of T_1 and T_2, which are the only contributions to the cw-ESR linewidth, constitutes a convincing evidence of the metallic nature of OP-Rb₁C₆₀. The drastic increase (decrease) of the linewidth (T_2) below \valunit{40}{K} is interpreted in terms of an \qut{electronic dimerization}.