Ground state of Ce$_{3}$Bi$_{4}$Pd$_{3}$ unraveled by hydrostatic pressure

TL;DR

This study uses hydrostatic pressure to reveal that Ce$_{3}$Bi$_{4}$Pd$_{3}$ is a narrow-gap Kondo insulator, clarifying its ground state and the dominant role of Kondo coupling over spin-orbit coupling.

Contribution

It experimentally demonstrates that Kondo coupling, not spin-orbit coupling, primarily determines the ground state of Ce$_{3}$Bi$_{4}$Pd$_{3}$, resolving previous conflicting theories.

Findings

Ce$_{3}$Bi$_{4}$Pd$_{3}$ becomes more insulating under pressure.

The zero-pressure gap increases quadratically with pressure.

Kondo coupling is the main tuning parameter in this class of materials.

Abstract

Noncentrosymmetric Ce$_{3}$Bi$_{4}$Pd$_{3}$ 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 prototypical Kondo insulator Ce$_{3}$Bi$_{4}$Pt$_{3}$: either Ce$_{3}$Bi$_{4}$Pd$_{3}$ 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 Ce$_{3}$Bi$_{4}$Pd$_{3}$ via electrical resistivity measurements under hydrostatic pressure, which is a clean symmetry-preserving tuning parameter that increases hybridization but virtually preserves spin-orbit coupling. Ce$_{3}$Bi$_{4}$Pd$_{3}$ becomes more insulating under pressure, which is a signature of Ce-based Kondo insulating materials. Its small zero-pressure gap increases quadratically with pressure, similar to the behavior observed in the series Ce$_{3}$Bi$_{4}$(Pt$_{1-x}$Pd$_{x}$)$_{3}$, 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 Ce$_{3}$Bi$_{4}$Pd$_{3}$ has a narrow-gap Kondo insulating ground state.