Coexistence of Light and Heavy Carriers Associated with Superconductivity and Antiferromagnetism in ${\mathrm{CeNi}}_{0.8}{\mathrm{Bi}}_2$ with a Bi Square Net

We found that the ZrCuSiAs-type crystal ${\mathrm{CeNi}}_{0.8}{\mathrm{Bi}}_2$ with a layered structure composed of alternate stacking of $[{\mathrm{CeNi}}_x\mathrm{Bi}(1){]}^{\delta +}$ and $\mathrm{Bi}(2{)}^{\delta -}$ exhibits a superconductive transition at $\sim 4\mathrm{K}$. The conductivities, magnetic susceptibilities, and heat capacities measurements indicate the presence of 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 ${\mathrm{CeNi}}_x\mathrm{Bi}(1)$ layers primarily correspond to the light and heavy electrons, respectively.

Figure 1

Crystal structures of (a) LaFeAsO and (b) ${\mathrm{CeNi}}_x{\mathrm{Bi}}_2$ belonging to the ZrCuSiAs type [1, 14]. The valence state of each ion in (b): $+3$ for Ce, $+1$ for Ni, $-3$ for Bi(1), and $-1$ for Bi(2). Since there is a large valence difference between Bi(1) and Bi(2), the ${\mathrm{Ce}}^{3+}$ that locates at sites between the two Bi layers is relaxed to the Bi(1) layers with larger negative charges, and the remaining Bi(2) forms a square net.

Figure 2

(a) Temperature dependence of the electrical resistivity ($\rho$) for ${\mathrm{CeNi}}_{0.8}{\mathrm{Bi}}_2$ at 0 Oe. The inset shows the $\rho \mathrm{\text{−}}T$ curves as a function of the magnetic field. (b) Temperature dependence of the magnetic susceptibility ($\chi$) under conditions of ZFC and FC at 10 Oe. The right-hand inset shows an enlargement around the transition under the condition of ZFC. Two measurement fields, 10 and 1000 Oe were used. The left-hand inset shows the field dependence of the magnetization at 2 K.

Figure 3

Magnetic field dependence of the heat capacity of ${\mathrm{CeNi}}_{0.8}{\mathrm{Bi}}_2$ below 15 K. The inset shows the $T^2$ dependence of the heat capacity per unit temperature of ${\mathrm{CeNi}}_{0.8}{\mathrm{Bi}}_2$ at 0 Oe.