Interaction of phonons with intraband electronic excitations and crystal field transitions in Raman spectra of (Nd,Eu,Gd)Ba2Cu3Oy crystals

• First Raman measurements of (Nd,Eu,Gd)Ba2Cu3Oy (NEG-123) superconductors.
• We found similarity between NEG-123 and Y-123 Raman spectra.
• We could disentangle contributions of phonons, free carriers and f-electrons.
• The spectra reflect interaction of phonons with free carriers and f-electrons.

Intraband electronic excitations, phonons, and crystal field transitions of two unique (Nd,Eu,Gd)Ba2Cu3Oy single crystals with different Eu/Gd ratio were studied by Raman spectroscopy. The spectra were measured above and below critical temperature. The phonon symmetries were determined from the angular dependence of the spectra. The line shapes of barium, planar oxygen, and apical oxygen ions’ vibrations were affected by interaction of the phonons with intraband electronic excitations. We fitted the spectra at all measured temperatures and disentangled the phonon contributions from those of the intraband electronic excitations and identified corresponding interference terms. Below Tc, a broad, superconductivity-induced high-frequency peak appeared in the spectra of both crystals. Damping of the Raman active phonons in our crystals correlated well with varying pinning disorder in the crystals.