Exploration of strongly correlated states in SmB6 through a comparison of its two-coil pick-up response to that of Bi2Se3

Authors of earlier studies on the Kondo insulator SmB6 revealed the presence of a bulk Kondo insulating gap between 30 and 50 K and the emergence of a conducting surface state only < 4 K. Here, we compare the two-coil mutual inductance pick-up response of a SmB6 single crystal with that of a conventional topological insulator, a Bi2Se3 single crystal. From these studies, we identify three distinct temperature regimes for SmB6, viz., (i) T T *(- 66 K), (ii) (- 40 K) T-g T < T*, and (iii) T < T-g. At T* in SmB6, we observe a peak in the temperature-dependent AC pick-up signal which corresponds to the peak in the broad hump feature in the bulk DC susceptibility measurements and features in the resistivity measurements. A dip in the pick-up signal at T-g in SmB6 correlates with the evidence for the opening of a bulk Kondo gap in transport measurements. In this paper on our study of the pick-up signal in SmB6, we suggest the presence of a thin (submicron-order thickness), high conducting surface layer from a temperature just below Tg. In this T regime in SmB6, the pick-up signal shows a distinct square root frequency (nu) dependence compared with the linear nu dependence found in Bi2Se3. Across all the different T regimes, distinct AC frequency dependence and scaling properties are observed. Our results suggest that, above T*, weak exchange interactions cause electrons to scatter from random ion sites. Electronic correlations gradually strengthen with the onset of Kondo-like hybridization, setting in from below T *, and at T-g, a strongly correlated Kondo gap opens in the bulk of the material. The appearance of the thin, high-conducting surface layer is nearly coincident with the onset of the bulk Kondo insulating state below Tg in SmB6.