Anomalous phonon self-energy effects in SmBa2Cu3Oy: A Raman study

We present a Raman study of the variation of the B-1g O2-O3 out-of-phase pl ane-oxygen vibration in SmBa2Cu3Oy with temperature. This mode shows an ano malously strong hardening of about 10-13 cm(-1) between 300 and 10 K for bo th the nonsuperconducting (gamma approximate to 6.0)and superconducting (ga mma approximate to 6.9) samples. At low temperature, new excitations at 90 and 187 cm(-1) were detected in the Raman spectra of the SmBa2Cu3O6.0 cryst al. Their position and intensity change with temperature in a manner typica l for coupled-phonon-crystal-held (CF) excitations. Based on these findings we suggest that the anomalous hardening of the Big phonon in SmBa2Cu3Oy is mostly due to its coupling to a Sm3+ CF transition at 193 cm(-1) found ear lier in inelastic-neutron-scattering experiments. [S0163-1829(98)06145-1].