Crystalline electric field study in putative topologically trivial rare-earth doped YPdBi compound

Topological states of matter have attracted a lot of attention recently due to their intriguing physical properties and potential applications. In particular, the family of half-Heusler compounds RMT (R = rare earth, M = Pt, Pd or Au, and T = Bi, Sb, Pb or Sn) has been predicted to display tunable topological properties via their cubic unit cell volume and/or the charges of the M and T atoms. In this work, we report electron spin resonance (ESR), along with complementary macroscopic experiments, in the putative topologically trivial rare-earth doped (Gd, Nd and Er) YPdBi. From magnetic susceptibility data analysis constrained by ESR results, we were able to extract the fourth (A4) and sixth (A6) order crystal field parameters (CFP) for YPdBi and compared them with those already reported to YPtBi, which is known as a topologically nontrivial compound. We observed that the sign of the CFP changes systematically from YPdBi to YPtBi, possibly due to the inversion of the valence and conduction bands at the Fermi level. The enhanced spin-orbit coupling in YPtBi, when compared to YPdBi, induces the band inversion that drives the system to a nontrivial topological state. This band inversion likely has an effect on the effective charges surrounding the magnetic dopants that are probed by the CFP.