Elastic Anomalies of Polycrystalline SmRu₄P₁₂ Associated with Metal–Insulator Transition

Abstract

The longitudinal and transverse elastic constants of polycrystalline SmRu₄P₁₂ have been measured as a function of temperature in the magnetic field up to 12 T. The transverse elastic constant shows a weak softening toward low temperatures. Both longitudinal and transverse elastic constants show a large anomaly below the metal–insulator transition T_MI=16 K. These elastic anomalies indicate the ground state of the crystalline electric field multiplet to be Γ₈, and that the quadrupole ordering is responsible for this metal insulator transition. The successive anomalies of SmRu₄P₁₂ have been clearly observed by ultrasonic measurements. An elastic anomaly was found at T^*, which is 14 K in the absence of a magnetic field. T_MI increases and T^* decreases under the application of the magnetic field. The anomaly at T^* is markedly enhanced by the application of a magnetic field.