Evidence of apical oxygen in artificially superconducting SrCuO2-BaCuO2 thin films: A Raman characterization

The artificially layered superlattices, Sr2BanCu2+nO4+2n+x (n=0,1,2,3) have been investigated by Raman spectroscopy. Raman frequency shifts were observed in the n=2 and n=3 films, while no vibrational modes were observed in the n=0 and n=1 films. The crystalline structures of the n=1 and n=1 films have an infinite-layered structure. The Raman peaks located at 604 cm(-1) in the n=2 film and at 587 cm(-1) in the n=3 film can be assigned to the apical oxygen vibration along the c axis. These observations indicate films with compositions n=2 and n=3 are superlattice structures with a Ba-O sublattice.