4$f$ crystal field ground state of the strongly correlated topological insulator SmB$_6$

TL;DR

This study uses advanced x-ray scattering to determine the crystal field ground state of SmB$_6$, revealing a $ ext{Gamma}_8$ quartet state that influences its topological properties, challenging previous theoretical predictions.

Contribution

It provides the first direct experimental confirmation of the $ ext{Gamma}_8$ ground state in SmB$_6$, clarifying its electronic structure and topological nature.

Findings

The $ ext{Gamma}_8$ quartet state is confirmed as the ground state.

Results contradict previous density functional theory calculations.

The ground state influences the topological properties of SmB$_6$.

Abstract

We investigated the crystal-electric field ground state of the 4$f$ manifold in the strongly correlated topological insulator SmB$_6$ using core level non-resonant inelastic x-ray scattering (NIXS). The directional dependence of the scattering function that arises from higher multipole transitions establishes unambiguously that the $\Gamma_8$ quartet state of the Sm $f^5$ $J$=$5/2$ configuration governs the ground-state symmetry and hence the topological properties of SmB$_6$. Our findings contradict the results of density functional calculations reported so far.