Quantifying boron diffusion during SmB6 film grown on silicon

Samarium hexaboride (SmB₆) is a topological Kondo insulator with a gap in the conduction band formed by the hybridization of the samarium 4f and 5d bands. This gives rise to an insulating bulk and a heavy, topologically protected Dirac surface state. While most previous studies of SmB₆ have investigated bulk crystals, the synthesis of epitaxial thin films presents new opportunities to tailor the surface termination, orientation, and strain, which may alter the behavior of the topologically non-trivial surface state.

In this work we use molecular beam epitaxy to grow sub-50 nm thick films of SmB₆ on (001)-oriented silicon substrates. Transport measurements show a resistance plateau below around 10 K, consistent with both bulk samples and thin films reported in the literature. Using atom probe tomography, we quantify the unintentional boron diffusion into the substrate. We find a conducting region with a boron concentration around 4x10¹⁹ B / cm³ near the film-substrate interface, which may provide a parallel conduction path at low-temperature, mimicking the presence of a topologically protected Dirac surface state.