OPTICAL STUDY OF THE SUPERCONDUCTOR-NONSUPERCONDUCTOR TRANSITION IN (L1,CE)2(BA,L2)2CU3O8+Z (L1 AND L2 = RARE-EARTHS)

In order to clarify the origin of electronic change in (L1,Ce)2(Ba,L2)2Cu3O8+z (L1L2 2:2:3) (L1 and L2 are rare-earth atoms), we have grown single crystals of EuEu 2:2:3, EuLa 2:2:3, and ErLa 2:2:3, and measured their Raman-scattering spectra and optical-reflectivity spectra. Comparing the spectra for superconducting EuEu 2:2:3 and nonsuperconducting ErLa 2:2:3, we can see no clear difference between them, whereas the reduced samples of EuEu 2:2:3 show a systematic change in both the Raman and the reflectivity spectra, as the oxygen content decreases. This implies that the hole concentration in nonsuperconducting ErLa 2:2:3 is large enough to realize superconductivity. It strongly suggests the possibility of superconductivity destruction for reasons other than a decrease in hole concentration, such as local lattice distortion.