Imaging Emergent Heavy Dirac Fermions of a Topological Kondo Insulator

Abstract

The interplay between strong electron interactions and band topology is a new frontier in the search for exotic quantum phases. The Kondo insulator SmB6 has emerged as a promising platform as its correlation-driven bulk gap is predicted to host topological surface modes entangled with f electrons, spawning heavy Dirac fermions . Unlike the conventional surface states of non-interacting topological insulators, heavy Dirac fermions are expected to harbor spontaneously generated quantum anomalous Hall states, non-Abelian quantum statistics, fractionalization, and topological order. However, the small energy scales required to probe heavy Dirac fermions have complicated their experimental realization. Here we use high-energy-resolution spectroscopic imaging in real and momentum space on SmB6. On cooling through 35 K, we observe the opening of an insulating gap that expands to 14 meV at 2 K. Within the gap, we image the formation of linearly dispersing surface states with effective masses reaching 410 ± 20 me. Our results demonstrate the presence of correlation-driven heavy surface states in SmB6, in agreement with theoretical predictions . Their high effective mass trans- lates to a large density of states near zero energy, which magnifies their susceptibility to the anticipated novel orders, and their potential utility.