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(SOC) in Kondo insulators remain elusive. The main reason is that variations of (chemical) pressure or doping strongly influence the Kondo coupling J(K) and the chemical potential mu-both essential parameters determining the ground state of the material-and thus possible lambda(SOC) tuning effects have remained unnoticed. Here, we present the successful growth of the substitution series Ce3Bi4(Pt1-xPdx)(3) (0 <= x <= 1) of the archetypal (noncentrosymmetric) Kondo insulator Ce3Bi4Pt3. The Pt-Pd substitution is isostructural, isoelectronic, and isosize, and it therefore is likely to leave J(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(SOC), which thus is the dominating tuning parameter in the series. Surprisingly, with increasing x (decreasing lambda(SOC)), we observe a Kondo insulator to semimetal transition, demonstrating an unprecedented drastic influence of the SOC. The fully substituted end compound Ce3Bi4Pd3 shows thermodynamic signatures of a recently predicted Weyl-Kondo semimetal.