Spectroscopic studies of candidate topological Kondo insulators and Weyl semimetals

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 T is well established [1]. Using STM, we performed local measurements on well identified, atomically flat, unreconstructed surfaces [2]. Spectroscopy down to 0.35 K revealed states around –6 mV and –2 mV within the hybridization gap, which are dominated by surface contributions [3]. Introducing magnetic impurities in samples (Sm_1-xR_x)B₆ with R = Gd represses the surface states on a much larger length scale compared to non-magnetic impurities R = Y [4]. The influence of Sm vacancies on the surface states as well as surface manipulation by focused ion beam (FIB) will also be discussed in detail.
Also of topical interest is the magnetic Kagome lattice Weyl semimetal Co₃Sn₂S₂ in which time-reversal symmetry breaking causes an intrinsic giant anomalous Hall effect, a chiral anomaly effect in the bulk, and Fermi arcs on the surfaces [5]. The spin-resolved local density of states is compared with band-structure calculations and reveals a signature for the nontrivial surface states around 50 mV [6].

^*in collaboration with M. V. Ale Crivillero, Y. Cheon, C. Felser, Z. Fisk, L. Jiao, D. Kasinathan, M. König, G. Li, C.-X. Liu, E. Liu, S. Rößler, P. F. S. Rosa, F. Steglich, Y. Sun, L. H. Tjeng and Q. Xu

[1] S. Rößler et al., Proc. Natl. Acad. Sci. USA 111, 4798 (2014).
[2] S. Wirth et al., Phys. Stat. Sol. B, doi: 10.1002/pssb.202000022 (2020).
[3] Lin Jiao et al., Nat. Commun. 7, 13762 (2016).
[4] Lin Jiao et al., Sci. Adv. 4, eaau4886 (2018).
[5] Enke Liu et al., Nat. Phys. 14, 1125 (2018).
[6] Lin Jiao et al., Phys. Rev. B 99, 245158 (2019).