RENORMALIZATION OF PHONONS IN A (Y PR)BA2CU3O7 SUPERLATTICE INVESTIGATED BY RAMAN-SPECTROSCOPY/

Raman measurements on a superconducting superlattice with a 2:1 sequen ce of YBa2Cu3O7 and PrBa2Cu3O7 layers revealed a new line in the spect ral region around 320 cm-1, which is interpreted as a combination of o dd lattice vibrations on the Y sublayers with a partial admixture of a n even parity mode on the Pr sublayer, becoming Raman active in the su perstructure. Its eigenvector is similar to a phonon from the interior of the Brillouin zone of the original lattice. No superconductivity-i nduced self-energy effects are observed for this phonon, although the IR-active counterparts of the individual Y sublayer vibrations in YBa2 Cu3O7 exhibit those effects.