Kondo Insulator to Semimetal Transformation Tuned by Spin-Orbit Coupling

Recent theoretical studies of topologically nontrivial electronic states in Kondo insulators have pointed to the importance of spin-orbit coupling (SOC) for stabilizing these states. However, systematic experimental studies that tune the SOC parameter $\lambda_{\rm{SOC}}$ in Kondo insulators remain elusive. The main reason is that variations of (chemical) pressure or doping strongly influence the Kondo coupling $J_{\text{K}}$ and the chemical potential $\mu$ -- both essential parameters determining the ground state of the material -- and thus possible $\lambda_{\rm{SOC}}$ tuning effects have remained unnoticed. Here we present the successful growth of the substitution series Ce$_3$Bi$_4$(Pt$_{1-x}$Pd$_x$)$_3$ ($0 \le x \le 1$) of the archetypal (noncentrosymmetric) Kondo insulator Ce$_3$Bi$_4$Pt$_3$. The Pt-Pd substitution is isostructural, isoelectronic, and isosize, and therefore likely to leave $J_{\text{K}}$ and $\mu$ essentially unchanged. By contrast, the large mass difference between the $5d$ element Pt and the $4d$ element Pd leads to a large difference in $\lambda_{\rm{SOC}}$, which thus is the dominating tuning parameter in the series. Surprisingly, with increasing $x$ (decreasing $\lambda_{\rm{SOC}}$), we observe a Kondo insulator to semimetal transition, demonstrating an unprecedented drastic influence of the SOC. The fully substituted end compound Ce$_3$Bi$_4$Pd$_3$ shows thermodynamic signatures of a recently predicted Weyl-Kondo semimetal.Comment: 6 pages, 5 figures plus Supplemental Materia

Kondo-like phonon scattering in thermoelectric clathrates

Thermoelectric clathrates host guest atoms that can rattle inside their surrounding cages, yielding unusual phononic properties. Ikeda et al. show that ab initio calculations fail to account for thermodynamic and thermal transport data and propose a Kondo-like mechanism to explain the discrepancy

The new heavy fermion compound Ce3_3Bi4_4Ni3_3

The family of cubic noncentrosymmetric 3-4-3 compounds has become a fertile ground for the discovery of novel correlated metallic and insulating phases. Here, we report the synthesis of a new heavy fermion compound, Ce$_3$Bi$_4$Ni$_3$. It is an isoelectronic analog of the prototypical Kondo insulator Ce$_3$Bi$_4$Pt$_3$ and of the recently discovered Weyl-Kondo semimetal Ce$_3$Bi$_4$Pd$_3$. In contrast to the volume-preserving Pt-Pd substitution, structural and chemical analyses reveal a positive chemical pressure effect in Ce$_3$Bi$_4$Ni$_3$ relative to its heavier counterparts. Based on the results of electrical resistivity, Hall effect, magnetic susceptibility, and specific heat measurements, we identify an energy gap of 65-70 meV, about 8 times larger than that in Ce$_3$Bi$_4$Pt$_3$ and about 45 times larger than that of the Kondo-insulating background hosting the Weyl nodes in Ce$_3$Bi$_4$Pd$_3$. We show that this gap as well as other physical properties do not evolve monotonically with increasing atomic number, i.e., in the sequence Ce$_3$Bi$_4$Ni$_3$-Ce$_3$Bi$_4$Pd$_3$-Ce$_3$Bi$_4$Pt$_3$, but instead with increasing partial electronic density of states of the $d$ orbitals at the Fermi energy. To understand under which condition topological states form in these materials is a topic for future studies.Comment: 18 pages, 7 figure

First-Order Phase Transition in a New CaCu5-Related Antimonide, CePt5Sb

A new CaCu(5) related antimonide, CePt(5)Sb, has been identified. This ternary compound undergoes a structural phase transition at about 80 K according to room- and low-temperature X-ray and neutron diffraction, and measurements of electrical resistivity, specific heat and magnetism. The room temperature phase forms a new rhombohedral structure, space group R (3) over bar, a = 0.53535(2) nm, c = 3.10814(12) nm and consists of alternating blocks of CaCu(5)- and MnCu(2)Al-type fragments that extend along the c-axis. The low-temperature phase is monoclinic, space group Cm, a = 0.91821(5) nm, b = 0.53696(1) nm, c = 1.08064(6) nm, beta = 107.40(1)degrees. The unit cells of both structures (orthohexagonal and monoclinic) are geometrically related via the transformation matrix a' = -b', b' = -a, c'=1/3b - 1/3c. Bulk properties elucidate the phase transition being of first-order and evidence Kondo interactions at low temperatures. © 2011, American Chemical Societ