Kondo coherence gap and superconductivity in the Ce_1-xLa_xRhSb system

Abstract

CeRhSb is a mixed valent Ce-based compound which shows a rapid rise in resistivity at low temperatures. This resistivity rise has been attributed to the opening of a gap in the electronic density of states. On the other hand, isostructural LaRhSb is a superconductor with T_c of about 2.5 K. We have investigated the system Ce_1-xLa_xRhSb to study the effect of La substitution for Ce on the gap formation in CeRhSb, and the effect of Ce substitution for La on the superconductivity in LaRhSb. It is observed that the rapid rise in resistivity, and hence the gap formation, is suppressed even when a small amount of La is substituted for Ce in CeRhSb, though susceptibility continues to show mixed valent behavior. This suggests that a coherent Kondo lattice state is essential for the gap formation in CeRhSb. On the La rich side, superconductivity is suppressed even by 0.5% replacement of La by Ce. In the intermediate region of substitution, a gradual transformation from a mixed valent to a Curie-Weiss behavior in the susceptibility is observed.