Molecular Beam Epitaxy Growth of SmB₆ Thin Films on Fluoride Substrates

The topological Kondo insulator SmB₆ hosts an insulating bulk and topologically-protected conducting surface states. Thin films can provide a more controlled platform to explore strongly correlated topological phenomena. Previous SmB₆ films on MgO are polycrystalline, while films on Si and Ge are limited by interfacial chemical intermixing that obscures electrical transport signatures. Fluoride substrates BaF₂ (tensile) and CaF₂ (compressive) eliminate this issue, offering clean interfaces and tunable strain for exploring the fundamental properties of SmB₆.

Here, we report the synthesis of SmB₆ thin films on fluoride substrates using molecular beam epitaxy (MBE). X-ray diffraction confirms phase-pure, (001)-oriented cubic SmB₆ without secondary phases, while Raman spectroscopy reveals characteristic B₆ octahedral vibrational modes at 89.6, 141.7, and 158.3 meV. Complementary transport measurements reveal a resistivity plateau below ~8 K, consistent with surface conduction. Compared to existing bulk samples and first-generation films, our phase-pure oriented hexaboride films and clean interfaces open a new pathway to control thickness and strain for understanding and control of correlated topological phenomena.