Probing the Surface States of SmB₆ Through Planar Tunneling Using Second Harmonic Detection Techniques

Samarium hexaboride (SmB₆), a candidate topological Kondo insulator (TKI), has proven itself to be a rich physical system associated with a vast array of complex physics. Below 4 K, the conductivity is dominated by surface states that appear to be topologically protected. Previous work has shown that these surface states do not span the entire gap region (as they do in conventional TIs such as Bi₂Se₃) [1] and display a sensitivity to Samarium deficiency [2], suggesting their topological protection is incomplete. To better understand the nature of these conducting surface states, we apply second harmonic detection techniques to planar tunnel junctions made on SmB₆ single crystals, providing a higher energy resolution and cleaner spectra than planar tunneling conductance. These data are also numerically deconvolved to remove thermal population effects and recover the electronic density of states. We discuss an antisymmetric signature at ±1 meV in the second harmonic spectra that appears with the low-temperature formation of conducting surface states in the context of muon spin rotation studies [3][4] which correlate this low energy signature to bulk antiferromagnetic excitations.

[1] W.K Park et al., PNAS 113, 6599 (2016)

[2] W.K. Park et al., PRB 103, 155125 (2021)

[3] K. Akintola et al., npj Quantum Materials 3, 36 (2018).

[4] P.K. Biswas et al., PRB 95, 020410 (2017)