Magnetic and nonmagnetic doping dependence of the conducting surface states in SmB_6

摘要

Kondo insulator SmB_6 has attracted attention because it can realize new topological phenomena driven by the interplay between strong correlation effect and topology. However, its topological nature is still under debate. To examine the topological aspect, we demonstrate the nonmagnetic La and magnetic Ce doping dependence of the resistance of SmB_6. Moreover, the resistance ratios of different thicknesses are analyzed to confirm the surface contribution. Lightly doped La samples show a purely conducting surface region at low temperature, whereas the lightly doped Ce samples do not have any conducting region at low temperature. Furthermore, based on the analysis of the electrical transport data of Sm_(1-x)La_xB_6 (0.0 ≤ x ≤ 1.0), an electronic phase diagram was found, composed of four regions: region Ⅰ (0.0 ≤ x ≤ 0.06), Ⅱ (0.1 ≤ x ≤ 0.15), Ⅲ (x ≈ 0.2), and Ⅳ (0.25 ≤ x ≤ 1.0). Region Ⅰ is characterized by the presence of conducting surface states, region Ⅱ is characterized by the insulating phase due to the d-f hybridization gap without the conducting surface state, region Ⅲ is characterized by the disappearance of the d-f hybridization gap and the existence of valence fluctuation, and region IV is a typical metallic state.