RAMAN MODES OF THE APICAL OXYGEN IN MERCURY-BASED SUPERCONDUCTORS

Recent studies suggest that the apical oxygen plays an important role in high-T-c superconductivity of mercury-based superconductors HgBa2Ca n-1CunO2n+2+delta [Hg-12(n-1)n]. Among strong Raman peaks at similar t o 570 and similar to 585 cm(-1), the mode at similar to 585 cm(-1) has been determined robe the A(1g) mode of the apical oxygen. However, th e origin of the mode near 570 cm(-1) is still in question. In order to clarify the origin of the 570 cm(-1) mode, we have carried out Raman measurements on the Hg1-xTlxBa2(Ca0.86Sr0.14)(2)Cu3O8+delta systems, w here the amount of the oxygen in the Hg/Tl-O plane is controlled by th e doping level of Tl ions. The results show that the 570 cm(-1) peak d oes not arise from the modes of the interstitial oxygens in the Hg/Tl- O plane, but from the A(1g)-type mode of the apical oxygen. From our a nalysis, it is shown that the 570 cm(-1) mode arises from the apical o xygen O-A with the neighboring interstitial oxygen O-delta, while the 585 cm(-1) mode is from the O-A without the nearest O-delta neighbor. We conclude that the apical oxygens in the Hg-12(n-1)n systems can hav e two distinctive sets of O-delta environment.