STM studies of candidate topological Kondo insulator SmB₆

SmB₆ has been proposed a topological Kondo insulator with nontrivial surface states inside a bulk hybridization gap. Experimentally, hybridization between localized 4f and conduction band states at low temperatures is well established [1]. Using STM, we performed local measurements on well identified, atomically flat, unreconstructed surfaces [2]. Tunneling spectroscopy down to 0.35 K revealed sharp peak-like features with a strong temperature dependence within the hybridization gap. The features around –6 mV and –2 mV are dominated by surface contributions to the local density of states [3]. These surface states are robust in the vicinity of randomly occurring non-magnetic impurities, while introducing magnetic impurities in samples (Sm_1-xR_x)B₆ with R = Gd influences the surface states on a much larger length scale compared to non-magnetic impurities [4].
Another material of topical interest is the magnetic Kagome lattice Weyl semimetal Co₃Sn₂S₂ in which time-reversal symmetry breaking causes fascinating physics [5]. The measured local density of states reveals a semimetallic gap of ∼300 mV, verified as the gap in the spin-minority band using spin-resolved tunneling spectra [6].
Work conducted in collaboration with Y. Cheon, C. Felser, C. Guo, G. Li, E. Liu, Y. Sun, L. H. Tjeng, Q. Xu, and H. Yuan.

[1] S. Rößler et al., Proc. Natl. Acad. Sci. USA 111, 4798 (2014).
[2] S. Rößler et al., Phil. Mag. 96, 3262 (2016).
[3] Lin Jiao et al., Nature Commun. 7, 13762 (2016).
[4] Lin Jiao et al., Sci. Adv. 4, eaau4886 (2018).
[5] Enke Liu et al., Nature Phys. 14, 1125 (2018).
[6] Lin Jiao et al., Phys. Rev. B 99, 245158 (2019).