TEMPERATURE-DEPENDENCE OF THE LINEWIDTHS OF THE RAMAN-ACTIVE PHONONS OF YBA2CU3O7 - EVIDENCE FOR A SUPERCONDUCTING GAP BETWEEN 440 AND 500 CM-1

The linewidths and frequencies of three Raman-active phonons have been measured in twin-free single crystals of YBa2Cu3O7. Below T(c), the phonon at 340 cm-1 sharpens dramatically, the phonon at 440 cm-1 sharpens slightly, and the phonon at 500 cm-1 broadens. The temperature dependence of the phonon linewidths places the superconducting energy gap (2-DELTA) between 440 and 500 cm-1, or 2-DELTA = (6.8-7.7)k(B)T(c). Based upon the observed change in linewidth, the electron-phonon coupling strength of the 340-cm-1 phonon is estimated to be between 0.6 and 0.8.