EFFECTS OF ZN SUBSTITUTION FOR CU ON RAMAN PHONON ANOMALIES IN DOUBLE-CHAIN YBA2CU4O8 SUPERCONDUCTORS

We report on a Raman scattering investigation of Zn-substituted cerami c YBa2Cu4-xZnxO8 (x=0-0.05) superconductors with T-c between 80 and 44 K. Anomalous temperature behavior of phonon frequencies and Linewidth s of the Raman-active Ba, plane-oxygen and apical-oxygen modes are obs erved both around 150 K, and below T-c for all samples. The above-T-c anomaly, which is almost independent of Zn content, can be correlated with recently reported Y-89 NMR experiments that show the above T-c sp in-gap is only locally suppressed by the low levels of Zn doping consi dered here. The superconductivity related renormalizations of the Ba a nd plane-oxygen phonons are also largely unaffected by a decrease in T -c from 80 to 44 K, indicating a complicated relation between these ph onon anomalies and the superconducting gap 2 Delta. An interpretation within the framework of the Zeyer-Zwicknagel theory (or other similar electron-phonon coupling models) would indicate that 2 Delta is larger than about 8.7kT(c) in YBa2Cu4-xZnxO8.