Universal Behaviors of the Phonon Thermal Conductivity Associated with Charge=Orbital Ordering in Transition-Metal Oxides

We studied the thermal transport properties of transition-metal oxides, which have partially filled t_2g orbitals of transition metals and exhibit intriguing phase transitions caused by orbital=charge ordering. We found that the temperature (T) dependence of the phonon thermal conductivity κ_p exhibits a universal behavior for all compounds; κ_p(T) decreases with decreasing T above the transition temperature T_c, whereas it is enhanced below T_c. This result implies that orbital=charge ordering in transition-metal oxides can be characterized by a unique T dependence of the phonon thermal conductivity.