RAMAN-SCATTERING STUDIES OF ULTRATHIN-LAYER YBA2CU3O7 PRBA2CU3O7 SUPERLATTICES/

We present Raman scattering studies of c-oriented ultrathin-layer supe rconducting (YBa2Cu3O7)m/(PrBa2Cu3O7)n superlattices. For the superlat tice with (m = 2, n = 1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm-1. It is interpreted as a mode repre senting a combination of IR optical phonons of the Y-sublayers with an admixture of a B1g type Raman active vibration in the Pr sublayers. T his new line, which is similar to those from the interior of the Brill ouin zone of the original lattice, does not exhibit superconductivity- induced self-energy effects, although its counterpart in the pure subs tance does. No additional line is found in the (m = 1, n = 2) superlat tice in the same region, supporting our interpretation for the (m = 2, n = 1) sample.