Raman scattering investigation of β-pyrochlore osmium oxides, AOs2O6 (A=K, Rb, and Cs)

Abstract

Raman scattering spectra of RbOs2O6 and CsOs2O6 have been measured from 4 K to 300 K. Among six Raman active modes, we focus on T2g mode of alkaline atoms and Eg mode of oxygen. Width of the T2g mode becomes quite large in KOs2O6. This is caused by very lower-frequency fluctuation and a candidate of the fluctuation is T1u mode, which is another vibration of alkaline atoms. Large frequency changes of the Eg mode are found in KOs2O6 and RbOs2O6 in the temperature dependence. The large changes relate to low-frequency oxygen modes, which will be Eu mode. Therefore, the frequency of the T1u mode becomes very small in KOs2O6, and the frequency of the Eu mode becomes small in KOs2O6 and RbOs2O6. Since only KOs2O6 is considered as a strong-coupling superconductor, the T1u mode will play a very important role in superconductivity.