Raman spectroscopy study of the interface structure in (CaCuO_2)_n/(SrTiO_3)_m superlattices

摘要

Raman spectra of CaCuO_2/SrTiO_3 superlattices show clear spectroscopic marker of two structures formed in CaCuO_2 at the interface with SrTiO_3. For non-superconducting superlattices, grown in low oxidizing atmosphere, the 425 cm~(-1) frequency of oxygen vibration in CuO_2 planes is the same as for CCO films with infinite layer structure (planar Cu-O coordination). For superconducting superlattices grown in highly oxidizing atmosphere, a 60 cm~(-1) frequency shift to lower energy occurs. This is ascribed to a change from planar to pyramidal Cu-O coordination because of oxygen incorporation at the interface. Raman spectroscopy proves to be a powerful tool for interface structure investigation.