Ground state of Ce3Bi4Pd3 unraveled by hydrostatic pressure

Noncentrosymmetric Ce3Bi4Pd3 has attracted a lot of attention as a candidate for strongly correlated topological material, yet its experimental ground state remains a matter of contention. Two conflicting scenarios have emerged from a comparison to the prototypical Kondo insulator Ce3Bi4Pt3: Either Ce3Bi4Pd3 is a spin-orbit-driven topological semimetal or a Kondo insulator with smaller Kondo coupling than its Pt counterpart. Here, we determine the ground state of Ce3Bi4Pd3 via electrical resistivity measurements under hydrostatic pressure, which is a clean symmetry-preserving tuning parameter that increases hybridization but virtually preserves spin-orbit coupling. Ce3Bi4Pd3 becomes more insulating under pressures up to 2.3 GPa, which is a signature of Ce-based Kondo insulating materials in the considered pressure range. Its small zero-pressure gap increases quadratically with pressure, similar to the behavior observed in the series Ce3Bi4(Pt1-xPdx)3, which indicates that Pt substitution and applied pressure have a similar effect. Our result not only demonstrates that Kondo coupling, rather than spin-orbit coupling, is the main tuning parameter in this class of materials, but it also establishes that Ce3Bi4Pd3 has a narrow-gap Kondo insulating ground state.