Robust topological surface state in Kondo insulator SmB6 thin films

Fabrication of smooth thin films of topological insulators with true insulating bulk are extremely important for utilizing their novel properties in quantum and spintronic devices. Here, we report the growth of crystalline thin films of SmB 6 , a topological Kondo insulator with true insulating bulk, by co-sputtering both SmB 6  and B targets. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy indicate films that are polycrystalline with a (001) preferred orientation. When cooling down, resistivity ρ shows an increase around 50 K and saturation below 10 K, consistent with the opening of the hybridization gap and surface dominated transport, respectively. The ratio ρ 2K /ρ 300K  is only about two, much smaller than that of bulk, which indicates a much larger surface-to-bulk ratio. Point contact spectroscopy using a superconductor tip on SmB 6  films shows both a Kondo Fano resonance and Andeev reflection, indicating an insulating Kondo lattice with metallic surface states.

The authors acknowledge fruitful discussions with V. Galitski at the University of Maryland, and T. Mcqueen at John Hopkins University. This work was supported by ONR N00014-13-1-0635 and NSF DMR 1410665. I.T. and S.C. also acknowledge support by the Duke University Center for Materials Genomics.