Phonon-glass-like behavior of magnetic origin in single-crystal Tb2Ti2O7

We report a study on the thermal conductivity (kappa) of Tb2Ti2O7 single crystals at low temperatures. It is found that in zero field this material has an extremely low phonon thermal conductivity in a broad temperature range. The mean free path of phonons is even smaller than that of amorphous materials and is 3-4 orders of magnitude smaller than the sample size at 0.3 K. The strong spin fluctuation of the spin-liquid state is discussed to be the reason of the strong phonon scattering. The magnetic-field dependence of kappa and comparison with Y2Ti2O7 and TbYTi2O7 confirm the magnetic origin of this phonon-glass-like behavior.