# Irreversible proliferation of magnetic moments at cleaved surfaces of the topological Kondo insulator SmB6

## TL;DR

This study reveals that the magnetic moments on the surface of the topological Kondo insulator SmB6 irreversibly increase over time after cleaving, indicating persistent surface magnetic evolution linked to its topological properties.

## Contribution

It provides the first evidence of irreversible surface magnetic moment growth in SmB6 using XAS and RIXS, highlighting surface magnetic dynamics in topological Kondo insulators.

## Key findings

- Surface magnetic moments grow irreversibly over time.
- Surface-sensitive spectra show increased large-moment atomic states.
- Surface magnetic evolution exceeds changes in 4f orbital occupation.

## Abstract

The compound SmB$_6$ is the best established realization of a topological Kondo insulator, in which a topological insulator state is obtained through Kondo coherence. Recent studies have found evidence that the surface of SmB$_6$ hosts ferromagnetic domains, creating an intrinsic platform for unidirectional ballistic transport at the domain boundaries. Here, surface-sensitive X-ray absorption (XAS) and bulk-sensitive resonant inelastic X-ray scattering (RIXS) spectra are measured at the Sm N$_{4,5}$-edge, and used to evaluate electronic symmetries, excitations and temperature dependence near the surface of cleaved samples. The XAS data show that the density of large-moment atomic multiplet states on a cleaved surface grows irreversibly over time, to a degree that likely exceeds a related change that has recently been observed in the surface 4f orbital occupation.