Spin and charge dynamics in the Cu-O chains of YBa2Cu4O8

We report an NQR-NMR study of the chain copper and apex oxygen in the high- temperature superconductor YBa2Cu4O8. Above T-c, the temperature dependence s of the Cu spin-lattice relaxation rate and the Knight shift are quantitat ively described in the framework of the one-dimensional electron gas model, where the anisotropy and the correlation of the chain electron system are taken into account. Electric-field-gradient fluctuations due to charge carr iers in the chains contribute partly to the chain Cu relaxation and dominat e the apex oxygen relaxation. The different temperature dependences of the magnetic and quadrupolar relaxation rates of the chain Cu seem to confirm t he separation of low-energy spin and charge excitations (spin-charge separa tion), expected in the framework of the one-dimensional electronic gas mode l. Finally, we present experimental evidence that below T-c the Cu-O chains become superconducting through the proximity effect. [S0163-1829(99)03329- 9].