Temperature-dependent Raman study of the spin-liquid pyrochlore Tb2Ti2O7

Temperature-dependent Raman-scattering studies of Tb(2)Ti(2)O(7) geometrically frustrated pyrochlore are presented. The Raman spectra have shown softening of the majority of modes upon cooling in the whole temperature range studied and large decrease in linewidths. These changes have been analyzed in terms of phonon-phonon anharmonic interactions. A departure from the expected behavior has been observed at low temperatures for the A(1g) mode, which is attributed to the spin-phonon coupling. The Raman studies have also revealed an unusual temperature dependence of the modes observed in the 290-350 cm(-1) range. This behavior has been attributed to a very strong coupling between the crystal-field excitations of the Tb(3+) 4f electrons and the F(2g) mode, which is a distinct feature of Tb(2)Ti(2)O(7) spin-liquid material among the family of rare-earth titanates. Our studies have also shown several uncoupled crystal-field excitations, which has provided information on energy levels of the (7)F(5) manifold.