INTENSITY ANOMALIES OF RAMAN-ACTIVE PHONONS IN THE SUPERCONDUCTING STATE OF YBA2CU3O7-DELTA

We report anomalous intensity increases, by up to a factor of 2, of Raman-active phonons in YBa2Cu3O7-delta below the superconducting transition temperature. This effect can be explained as a superconductivity-induced resonant Raman process stemming from the resonance of the phonons with the superconducting gap. In the normal state a continuous increase of the Raman efficiency was observed for most phonons upon cooling from 300 K to T(c). All relative changes in intensity seem to be rather independent of the exciting laser energy used (1.92, 2.34, and 2.60 eV).