Topological nature of the Kondo insulator SmB$_6$ and its sensitiveness to Sm vacancy

TL;DR

This study investigates how Sm vacancies affect the topological surface states of SmB$_6$, revealing that disorder influences the coherence of these states despite the bulk gap remaining stable, highlighting the interplay of correlations and topology.

Contribution

It provides new spectroscopic evidence that Sm vacancies disrupt the coherence of topological surface states in SmB$_6$, challenging the notion of their robustness against disorder.

Findings

Bulk hybridization gap remains stable with up to 1% Sm deficiency.

Surface states show altered temperature behavior in Sm-deficient crystals.

Topological surface states remain incoherent due to interaction with spin excitons.

Abstract

The true topological nature of the Kondo insulator SmB$_6$ remains to be unveiled. Our previous tunneling study not only found evidence for the existence of surface Dirac fermions, but it also uncovered that they inherently interact with the spin excitons, collective excitations in the bulk. We have extended such a spectroscopic investigation into crystals containing a Sm deficiency. The bulk hybridization gap is found to be insensitive to the deficiency up to 1% studied here, but the surface states in Sm-deficient crystals exhibit quite different temperature evolutions from those in stoichiometric ones. We attribute this to the topological surface states remaining incoherent down to the lowest measurement temperature due to their continued interaction with the spin excitons that remain uncondensed. This result shows that the detailed topological nature of SmB$_6$ could vary drastically in the presence of disorder in the lattice. This sensitiveness to disorder is seemingly contradictory to the celebrated topological protection, but it can be understood as being due to the intimate interplay between strong correlations and topological effects.