Exploring Characteristic Electronic States in Filled Skutterudites by Ultrasonic Measurements –Multipole Ordered State in SmRu4P12–

Filled skutterudites show various interesting physical properties, such as unconventional superconductivity, anomalous magnetism, metal–insulator transition, heavy fermion behavior and so on. We have investigated the multipole ordering state of SmRu 4 P 12 by ultrasonic measurements under extreme conditions of low temperature, high pressure and high magnetic field by pulsed method, so far. Recently, the angle dependence of the elastic constant has been measured. The elastic constant shows interesting and peculiar angle dependence below the metal–insulator transition temperature in the magnetic field. It will enable us to reveal characteristic multipole ordered state in SmRu 4 P 12 . In this paper, we will report recent status of the multipole ordered state of SmRu 4 P 12 , and discuss the recent results of our elastic constant measurements and the relation to the octupole ordering scenario proposed for this system.