Effect of Sn doping on the coherent Kondo gap in CeRhSb and the emergence of a non-Fermi-liquid state inCeRhSb1−xSnx

Abstract

CeNiSn and CeRhSb are known as heavy-fermion (Kondo) insulators with a narrow energy gap in the heavy-quasiparticle density of states. The gap appearance is very sensitive to the number of carriers present. Existing studies of alloying show that replacement of Sn ions of CeNiSn by Sb leads to a formation of the weakly ferromagnetic Kondo lattice, whereas CeRhSn has a non-Fermi-liquid ground state. In view of the contrasting behavior of the Sb-containing and Sn-containing systems, we investigate the solid solutions $\mathrm{Ce}\mathrm{Rh}{\mathrm{Sb}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$, to determine the dependence of the electronic properties on the number of the conduction electrons and, in particular, on the gap formation in CeRhSb, as well as on the nature of the ground state across the series. We present the structural properties, the electronic band structure, and the resistivity $[\ensuremath{\rho}(T)]$ data for $\mathrm{Ce}\mathrm{Rh}{\mathrm{Sb}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$. The system exhibits in the Sb-rich regime a variety of $\ensuremath{\rho}(T)$ dependencies at the low temperatures, namely, an activated behavior $\ensuremath{\rho}={\ensuremath{\rho}}_{0}\phantom{\rule{0.2em}{0ex}}\mathrm{exp}({\mathrm{\ensuremath{\Delta}}}_{\mathrm{coh}}∕{k}_{B}T)$ for $x=0$ and $x=0.1$, $\ensuremath{\rho}\ensuremath{\propto}{T}^{2}$ for $x=0.2$, which transform into the dependences $\ensuremath{\rho}\ensuremath{\propto}\ensuremath{-}\mathrm{ln}\phantom{\rule{0.2em}{0ex}}T$ for $x=0.9$, and $\ensuremath{\rho}\ensuremath{\propto}{T}^{ϵ}$ (where $ϵ\ensuremath{\sim}1$) for Sn-rich samples. Furthermore, the resistivity of both the CeRhSb and the Sn-substituted alloys indicates a coherent Anderson-lattice nature of the ground state. We also present the $3d$ x-ray photoemission (XPS) spectra, from which we determine the $f$-shell occupation. Analysis of the $3{d}^{9}{f}^{2}$ weight in the $3d$ XPS spectra, using the Gunnarsson-Sch\"onhammer model, suggests that the hybridization ${\mathrm{\ensuremath{\Delta}}}_{fs}$ is about 150 meV across the $\mathrm{Ce}\mathrm{Rh}{\mathrm{Sb}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ series. The XPS valence band spectra (high-energy probe) for $\mathrm{Ce}\mathrm{Rh}{\mathrm{Sb}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ are related to the linear muffin tin orbital calculations. We interpret the XPS data in terms of the band-structure calculations, whereas the $\ensuremath{\rho}(T)$ and the magnetic susceptibility $\ensuremath{\chi}(T)$ data (low-energy probes) in terms of Anderson-lattice physics.