Hybridization gap in ${\mathrm{Ce}}_3$${\mathrm{Bi}}_4$${\mathrm{Pt}}_3$

We present resistivity ρ(T), susceptibility χ(T), and specific heat C(T) data for ${\mathrm{Ce}}_3$ ${\mathrm{Bi}}_4$ ${\mathrm{Pt}}_3$. The susceptibility exhibits a broad maximum centered near 80 K, typical of a somewhat-heavy-electron compound; were the material metallic, a linear coefficient of specific heat γ=75 mJ/mol Ce ${\mathrm{K}}^2$ would be expected. However, the compound is InotR metallic, as indicated by its resistivity which rises to large values at low temperatures and exhibits activated behavior with an activation energy Δ/${\mathit{k}}_{\mathit{B}}$=35 K. By analogy to ${\mathrm{SmB}}_6$ and ${\mathrm{YbB}}_{12}$, this energy gap arises from 4f-electron–conduction-electron hybridization. Due to the gap, electronic excitations are suppressed at low temperatures and the specific heat is smaller than in nonmagnetic ${\mathrm{La}}_3$ ${\mathrm{Bi}}_4$ ${\mathrm{Pt}}_3$. Alloying with lanthanum ((${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{La}}_{\mathit{x}}$ ${)}_3$ ${\mathrm{Bi}}_4$ ${\mathrm{Pt}}_3$) decreases the resistivity and increases the specific heat towards the value expected for the metallic case; i.e., for moderate alloying (x=0.07) the behavior is that of a moderately disordered heavy-electron metal. We argue that lattice periodicity is an essential requirement for the formation of the hybridization gap.