Probing orbital order-disorder transition in CaCu_3Ti_4O_(12) and SrCu_3Ti_4O_(12) by Raman Spectroscopy

摘要

Raman Scattering studies on CaCu_3Ti_4O_(12) and SrCu_3Ti_4O_(12) compounds is carried out at low temperature (10 K) and high wavenumber (4000?cm~(-1)). The high frequency Raman data below ～130 K shows a broad Raman mode in both the compounds that is attributed to the orbital excitations. The polarization and excitation energy analysis further supports the orbital excitation as the origin of broad high wavenumber mode (～ 2300?cm~(-1)). The observed resemblance to Raman mode in titanates indicates universality of the electronic excitations in perovskites. This broad feature in high energy spectra is accompanied with an extra phonon mode in low frequency spectra in the SrCu_3Ti_4O_(12) compound.