TEMPERATURE-DEPENDENCE OF THE PHONON FREQUENCIES AND LINEWIDTHS OF YBA2(CU1-XMX)(4)O-8 FOR M = NI AND ZN

We report on the temperature dependence of Raman spectra for YBa2(Cu1- xNix)(4)O-8 (x=0-0.02) and YBa2(Cu1-xZnx)(4)O-8 (x=0-0.01) polycrystal s. Below the transition to the superconducting state an anomalous abru pt mode softening and line broadening of the Ba vibrational mode at 10 0 cm(-1) are observed in the Raman spectra. The largest shift is obser ved in the undoped Y1:2:4 samples in which the frequency softens by ap proximately 5.5 cm(-1) between T-c and 10 K while the amount of soften ing is greatly reduced with increasing dopant M concentration. This ca n be interpreted by considering that under the presence of two gap str ucture for Y1:2:4 the smaller gap 2 Delta(1) is near or just above the Ba phonon frequency in undoped samples and its energy decreases with Ni or Zn doping. These phonon anomalies are consistent with the Zeyher -Zwicknagl model assuming the s-wave symmetry of pair function.