Successive phase transitions and energy-gap formation in CeRhAs

Abstract

Magnetic, transport, and x-ray diffraction measurements on single-crystal CeRhAs, the so-called Kondo insulator, have revealed successive transitions at ${T}_{1}=370,$ ${T}_{2}=235,$ and ${T}_{3}=165\mathrm{K}.$ 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 (0,1/3,1/3) and (1/3,0,0) appear at $T<{T}_{2}.$ 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.