No abstract

Magnetic, transport, and x-ray diffraction measurements on single-crystal CeRhAs, the so-called Kondo insulator, have revealed successive transitions at T 1 ϭ370, T 2 ϭ235, and T 3 ϭ165 K. Below T 1 , the unit cell is doubled along the b and c axes. Thereby, the resistivity jumps upwards and magnetic susceptibility in all the directions drops. Superlattice reflections at ͑0,1/3,1/3͒ and ͑1/3,0,0͒ appear at TϽT 2. The latter suddenly increases below T 3 where a transport gap is enhanced. These observations indicate that the gap formation is intimately related to lattice modulations.