Surface-dominated conduction up to 240 K in the Kondo insulator SmB₆ under strain

SmB₆ is a strongly correlated mixed-valence Kondo insulator with a newly discovered surface state, proposed to be of non-trivial topological origin. However, the surface state dominates electrical conduction only below T^∗ ≈ 4 K (ref. ), limiting its scientific investigation and device application. Here, we report the enhancement of T^∗ in SmB₆ under the application of tensile strain. With 0.7% tensile strain we report surface-dominated conduction at up to a temperature of 240 K, persisting even after the strain has been removed. This can be explained in the framework of strain-tuned temporal and spatial fluctuations of f-electron configurations, which might be generally applied to other mixed-valence materials. We note that this amount of strain can be induced in epitaxial SmB₆ films via substrate in potential device applications.