Strong-coupling effects in alkali-metal-doped C60.

Mazin I.I., Dolgov O.V., Golubov A., Shulga S.V.

Various experiments indicate that K3C60 and Rb3C60 are in the strong-coupling regime. There is also both theoretical and experimental evidence for a large coupling of high-frequency intramolecular phonons with the electrons. If only these phonons are relevant, it is difficult to explain the relatively low Tc. This paradox can be resolved by introducing additional coupling with the low-lying intermolecular modes. Such a model also provides a consistent explanation of the tunneling experiments, and of the non-BCS behavior of the critical fields, penetration depth, and NMR relaxation time.

Physical Review B, 47 538-41, 1993.

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