Scanning Tunneling Spectroscopy and Imaging of Topological Kondo Insulators

Topological insulators host spin-polarized surface states which robustly span the band gap and hold promise for novel applications. Recent theoretical predictions have suggested that topologically protected surface states may similarly span the hybridization gap in some strongly correlated heavy fermion materials, particularly $SmB_6$. Scanning tunneling spectroscopy (STS) is a powerful tool for studying topological materials because it is directly sensitive to the surface states of interest, and their scattering processes. Here we present the first atomic resolution spectroscopic study of the cleaved surface of $SmB_6$ [1]. Using a combination of real space imaging and filled and empty state spectroscopy, we reveal a robust hybridization gap that universally spans the Fermi level on four distinct surface morphologies despite shifts in the f band energy. Using a cotunneling model, we separate the density of states of the hybridized bands from which the predicted topological surface states must be disentangled. Our technique lays the groundwork for understanding the first strongly correlated topological insulator, and implements a generally applicable method to quantitatively understand a wider class of Kondo insulators.\\[4pt] [1] arXiv:1308.1085