Planar tunneling spectroscopy of the topological Kondo insulator SmB${}_6$

Abstract

Several technical issues and challenges are identified and investigated for the planar tunneling spectroscopy of the topological Kondo insulator SmB${}_6$. Contrasting behaviors of the tunnel junctions prepared in two different ways are analyzed and explained in detail. The conventional approach based on an AlO${}_{\text{x}}$ tunnel barrier results in unsatisfactory results due to the inter-diffusion between SmB${}_6$ and deposited Al. On the contrary, plasma oxidation of SmB${}_6$ crystals produces high-quality tunnel barriers on both (001) and (011) surfaces. Resultant conductance spectra are highly reproducible with clear signatures for the predicted surface Dirac fermions and the bulk hybridization gap as well. The surface states are identified to reside on two or one {\it distinguishable} Dirac cone(s) on the (001) and (011) surface, respectively, in good agreement with the recent literature. However, their topological protection is found to be limited within the low energy region due to their inevitable interaction with the bulk excitations, called spin excitons, consistent with a recent theoretical prediction. Implications of our findings on other physical properties in SmB${}_6$ and also other correlated topological materials are remarked.

arXiv comment11 pages, 11 figures, published in Phys. Rev. B

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• Topo-fermiology
• Spectroscopic Evidence for the Direct Involvement of Local Moments in the Pairing Process of the Heavy-Fermion Superconductor CeCoIn${}_5$
• Electrical properties of SmB${}_6$ thin films prepared by pulsed laser deposition from a stoichiometric SmB${}_6$ target
• Topological nature of the Kondo insulator SmB${}_6$ and its sensitiveness to Sm vacancy
• An STM perspective on hexaborides: Surface states of the Kondo insulator SmB${}_6$
• Topological surface states in the Kondo insulator YbB${}_{12}$ revealed via planar tunneling spectroscopy