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

The compound SmB6 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 SmB6 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 spectra are measured at the Sm N4,5 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