Raman light scattering on YBa2Cu3O7/La2/3Ca1/3MnO3 superlattices

Artificial superlattice (SL) structures offer a possibility of combining antagonistic order parameters such as superconductivity (SC) and ferromagnetism (FM). It was recently observed that the interface between YBa2Cu3O7 (YBCO) and La2/3Ca1/3MnO3 (LCMO) exhibits an unusual orbital reconstruction different than that of either YBCO or LCMO. Therefore, it is of fundamental interest to explore proximity and inverse-proximity effects that take place at the vicinity of the interface between the two systems using Raman scattering (RS). We have performed RS experiments on YBCO/LCMO SLs with different thicknesses of YBCO, i.e., 5-50 nm and constant thickness of LCMO (10 nm). We focus our study on the 230 cm-1 phonon, which arises from in-phase rotations of the MnO6 octahedra and the 340 cm-1 mode originating from out-of-phase vibrations of the oxygen atoms in the CuO2 planes of YBCO. Our T-dependence measurements revealed a strong anomaly in the phonon frequency and linewidth of these modes at the SC- and Curie transition temperatures. The anomaly we observe appears to be tied to a competition between electronic instabilities at the YBCO/LCMO interfaces and the bulk electronic properties of both layers.