Anomalous Raman shift in the ternary fullerides with t_1g states

Raman spectra have been studied on two kinds of highly doped fullerides of A_xBa₃C₆₀ (x=0,3;A=K, Rb) and K_xSm_2.75C₆₀ (x=0,3.25). It was found that the Raman spectra are essentially identical to each other for all ternary fullerides. The results show a crossover point at the boundary of t_1u and t_1g bands for the charge-transfer dependence of Raman shift. Particularly, the totally symmetric A_g(2) mode in t_1g fullerides cannot be understood by a simple extrapolation from the low-doped t_1u fullerides, where the A_g(2) mode follows a characteristic shift of ∼6.3 cm^-1 per elementary charge. The present result shows that the Raman spectra of t_1g states cannot be explained only by charge transfer.