Bulk and in-gap states in SmB6 revealed by high-field magnetotransport

We report on temperature-dependent magnetotransport experiments of ${\mathrm{SmB}}_{6}$ single crystals in high magnetic fields up to 33 T. Above the low-temperature plateau region in the zero-field resistivity, we find two distinct gapped regimes. The first is characterized by a temperature-independent gap ${\mathrm{\ensuremath{\Delta}}}_{2}$ that closes in the presence of a high magnetic field while the second regime, above $\ensuremath{\sim}8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, features an energy gap ${\mathrm{\ensuremath{\Delta}}}_{1}$ that is temperature dependent. In the entire temperature range, we observe an overall negative magnetoresistance that does not depend on the orientation of the crystalline plane with respect to the applied magnetic field with a maximum value at $T\ensuremath{\sim}6.2\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The regime of in-gap states is characterized by a low mobility, an anomalously high carrier concentration, and an enhanced nonlocal resistance that exceeds the expected classical value for a two-dimensional metallic conductor. Overall, our data can be interpreted in terms of a transition from bulk to in-gap dominated transport, but evidence of topological surface states is not observed.