Quantum Cafe: Laura H. Greene

Quantum Café is CCQ’s ongoing seminar series: open to all bona fide members of the greater NYC scientific community and held every second week, Quantum Café presents a series of informal, highly interactive talks, typically by external speakers, which present the most interesting recent developments and open questions in our field.

Title: The Topological Kondo Insulator SmB6: Surface States and Bulk Spin Excitons and The Dark Energy of Quantum Materials

Abstract: Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating behavior of the bulk arises from strong electron correlations, has recently attracted great attention owing to its possible topological nature; thereby harboring protected surface states. Although there is strong evidence for this, corroborative spectroscopic evidence was lacking; unlike in the weakly correlated counterparts, e.g., Bi2Se3. Our planar tunneling spectroscopy results obtained on the (001) and (011) crystal faces reveal the linear density of states (DOS) as expected for Dirac cones.  Our spectroscopic results also surprisingly reveal the bulk gap (below the surface state), whose signature can only arise from interactions with the bulk. We argue these are spin excitons, and above ~ 4 K, their thermal population keeps the surface state from being protected.