Coexistence of light and heavy carriers associated with superconductivity and anti-ferromagnetism in CeNi0.8Bi2 with a Bi square net

We found that the ZrCuSiAs-type crystal CeNi0.8Bi2 with a layered structure composed of alternate stacking of [CeNixBi(1)]{\delta}+ and Bi(2){\delta}- exhibits a superconductive transition at ~4 K, which was confirmed by zero resistance and the Meissner effect (shielding volume faction ~100% at 2 K). Heat capacity measurements revealed that the electron mass at the normal state (>5 K) is heavy ({\gamma} = 0.4 J mol-1 K-2) and a peak responsible for the anti-ferromagnetic ordering of Ce3+ 4f1 at ~5 K. These results indicate that there are two types of carriers with notable different masses, i.e., a light electron responsible for superconductivity and a heavy electron interacting with the Ce 4f electron. This observation suggests that 6p electrons of Bi(2) forming the square net and electrons in CeNixBi(1) layers primarily correspond to light and heavy electrons, respectively.