ABNORMAL RAMAN INTENSITY ENHANCEMENT OF CU-CU VIBRATION WITH FILM THICKNESS REDUCTION IN YBACUO7-DELTA ON LASRALO4

Raman spectra from ultra-thin films of YBa2Cu3O7-delta on LaSrAlO4 (00 1) (LSAO) substrates have been obtained by properly subtracting the su bstrate spectrum. It was found that the Raman intensities of the Cu-Cu vibration are drastically enhanced relative to the B-1g mode with the reduction of film thickness. This Raman intensity variation and some other changes in the Raman spectra are attributed to the fact that the oxygen deficient phases such as the orthorhombic-II (YBa2Cu3O6.5) are dominantly formed at the early stage of the film growth on LSAO. The gradually decrease of oxygen content with the reduction of film thickn ess explains the thickness dependence of T-c in this system.