Effects of La Substitution on the Energy Gaps and Superstructures of CeRhAs

Abstract

Magnetic, transport and specific-heat measurements of Ce 1- x La x RhAs ( x ≤0.1) have been performed. The host compound CeRhAs undergoes successive phase transitions with formation of superlattices at T 1 =360, T 2 =235, and T 3 =165 K, respectively. The transitions at T 1 and T 3 are associated with the formation of a wide gap of E g1 / k B =2200 K and a narrow one of E g2 / k B =310 K, respectively. All anomalies at T 1 , which are a jump in the specific heat C , a drop in the magnetic susceptibility χ and the activation-type behavior in the Hall coefficient, remain until x is increased up to 0.10, at which T 1 is depressed to 297 K. These observations indicate that both the phase transition at T 1 and the gap of E g1 remain up to x =0.10. Anomalies in C and χ at T 2 and T 3 , on the other hand, vanish at a small concentration x =0.01. The semiconducting behavior in both the electrical resistivity and thermopower below T 3 also disappears at x =0.02. These facts corroborate that the narrow gap of E g2 is quenched when the phase transition at T 3 disappears. The distinct effects on the phase transitions in Ce 1- x La x RhAs and CeRhAs 1- y Sb y indicate that coherent hybridization between Rh 4 d and As 4 p states is important for the formation of E g1 below T 1 .