Phonon dynamics of the geometrically frustrated pyrochloreY2Ru2O7investigated by Raman spectroscopy

We investigate temperature-dependent Raman spectra of the geometrically frustrated pyrochlore ${\mathrm{Y}}_{2}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$, which shows a spin-glass-like transition at ${T}_{G}\ensuremath{\sim}80\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Three discernable phonons appear around $315$, $410$, and $510\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ without any abrupt change in the number of Raman-active modes within the temperature range of 10--$300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Fitting each phonon with Lorentz oscillators, we examine the effects of temperature on phonon dynamics, in terms of the phonon frequency and the linewidth. The temperature dependence of the mode near $510\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ shows abnormal behavior below ${T}_{G}$, while the other two phonons follow the usual thermal effect. This behavior can be understood in terms of spin-phonon coupling. Considering the atomic modulations of the phonon mode showing abnormal behavior, the $510\text{\ensuremath{-}}{\mathrm{cm}}^{\ensuremath{-}1}$ phonon mode is isotropically coupled to the spin degree of freedom, while the other modes are not.