電荷密度波材料BaRuO3、BaIrO3、Sr2IrO4之光譜研究

[[abstract]]We report the Raman-scattering and optical reflectance measurements of single-crystalline BaRuO3, BaIrO3 and Sr2IrO4 as a function of temperature. These materials are interesting on account of their large spatial extent of 4d- and 5d-electron orbitals. The room-temperature Raman sprctra of BaRuO3 are consistent with those of the previous reports published in [Phys. Rev. B 65, 235113 (2002).]. By lowering the temperature and crossing the charge-density-wave (CDW) transitions, the lattice parameters of some certain phonon modes in BaIrO3 and Sr2IrO4 show abnormal behaviors, reflecting the strong electron-phonon coupling effects play an important role in the CDW state of these materials. Moreover, the on-set Coulomb repulsion energy U, the crystal-field splitting 10Dq,and the charge-transfer energy Δpd of Sr2IrO4 are estimated to be ~ 1.09, 2.94, and 3.20 eV from analyzing the optical conductivity data. Compared with the case of 3d and 4d, the parameter of U is decreasing, in agreement with the extended nature of the orbitals in the 5d oxides; 10Dq and Δpd are increasing, indicating the enhanced d-p hybridization.