Effects of Zn substitution for Cu on Raman phonon anomalies in double-chain YBa2Cu4O8 superconductors

Abstract

We report on a Raman scattering investigation of Zn-substituted ceramic YBa2Cu4−xZnxO8 (x=0-0.05) superconductors with Tc between 80 and 44 K. Anomalous temperature behavior of phonon frequencies and linewidths of the Raman-active Ba, plane-oxygen and apical-oxygen modes are observed both around 150 K, and below Tc for all samples. The above-Tc anomaly, which is almost independent of Zn content, can be correlated with recently reported Y89 NMR experiments that show the above Tc spin-gap is only locally suppressed by the low levels of Zn doping considered here. The superconductivity related renormalizations of the Ba and plane-oxygen phonons are also largely unaffected by a decrease in Tc from 80 to 44 K, indicating a complicated relation between these phonon anomalies and the superconducting gap 2Δ. An interpretation within the framework of the Zeyer-Zwicknagel theory (or other similar electron-phonon coupling models) would indicate that 2Δ is larger than about 8.7kTc in YBa2Cu4−xZnxO8. © 1996 The American Physical Society.

Source-reported materials — not catalogue approval

Similar papers