Crystal Field Effect on Superconducting Transition in Pr_<i>x</i>Os₄Sb₁₂

Abstract

We have succeeded in growing Pr x Os 4 Sb 12 single crystals under high pressure (∼4 GPa) for the first time, where the Pr site filling fraction is supposed to be enhanced. From the systematic measurement of the transport, magnetic, and thermal properties on the grown single crystals, we found a marked decrease in the onset superconducting transition temperature T c and a considerable increase in the 4 f -electron crystal field (CF) energy splitting between the ground state and the first excited state (Δ CF ), compared with those reported on the ambient-pressure grown single crystals. Furthermore, the mass enhancement is reduced in the high-pressure grown samples. The correlation between Δ CF and both T c and mass enhancement indicates the crucial role of conduction electron scattering accompanied by the CF excitation in the superconductivity of this compound.