SINGLE-SPIN FLUID, SPIN GAP, AND D-WAVE PAIRING IN YBA2CU4O8 - A NMR AND NQR STUDY

We present results of O-17 and Cu-63, Cu-65 nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR) studies in the normal a nd superconducting state of the 82-K superconductor YBa2Cu4O8. The var ious components of the Cu and 0 Knight-shift tensors show strong but s imilar temperature dependences over the temperature range from 8.5 to 300 K in both the CuO2 Planes and the chains, supporting the picture t hat there is only one spin component in the planes and the chains, alt hough with different susceptibilities. The oxygen data obey the Korrin ga relation. This may be interpreted as Fermi-liquid behavior of the e lectronic system far away from the anti-ferromagnetic wave vector. The temperature dependence of both the planar Cu and 0 shift tensors and the planar Cu spin-lattice relaxation rate suggest the opening of a ps eudo-spin-gap well above T(c). The very different temperature dependen ce of 1/T1 at the planar 0 and Cu sites points to the reduced role of the antiferromagnetic correlated spin fluctuations at the 0 site. The data favor the conclusion that YBa2CU4O8 is a d-wave superconductor. E vidence is provided by three data sets: the chain Knight shifts, the r atio of the planar copper and oxygen relaxation rates, and the individ ual low-temperature behavior of these rates.