Imaging Topologically Emergent Dirac States of a Kondo Insulator

Correlated topological matter is a frontier in the search for exotic quantum phases. Theory now predicts that heavy fermion systems, fertile grounds for discovery in strongly interacting electronic materials, may host such novel phases in the form of topological Kondo insulators. Within these systems, a correlation-driven gap protected by a bulk topological invariant is predicted to harbor emergent surface modes that are entangled with f-electrons, spawning heavy Dirac fermions. In stark contrast to conventional surface states of the non-interacting topological insulators, heavy Dirac fermions are expected to give rise to exotic Dirac liquid states, non-Abelian quantum statistics and topological order. In search of these strongly interacting topological states SmB₆ has recently emerged as the most promising candidate. However, no experiments have directly observed the correlated ground state and its emergent heavy Dirac fermions. Here we report the use of heavy fermion quasiparticle interference imaging and co-tunneling spectroscopy to resolve the topological nature of SmB₆. On cooling through T_Δ* ≈ 35 K we observe the opening of a Kondo insulator gap that expands to Δ* ≈ 10 meV at 2 K, in agreement with transport studies. Within the gap, momentum space imaging reveals flatly dispersing Dirac surface states with effective masses reaching m* = (330 ±20)m_e. Collectively, our observations demonstrate existence of a strongly correlated topological phase hosting the heaviest known Dirac fermions. The prodigious density of the Dirac states observed near zero energy magnifies their susceptibility to novel orders anticipated for interacting topological matter. Further, direct access at the material surface lifts prospects for manipulation and interface engineering necessary for next-generation quantum devices and universal topological quantum computation.