Advanced Photon Source

An Office of Science National User Facility

NST Seminar: The Topological Kondo Insulator SmB6: Surface States and Bulk Spin Excitons; plus…

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Laura G. Greene, National MagLab, Florida State University, and Center for Emergent Superconductivity
Daniel Lopez
Start Date: 
Monday, July 16, 2018
Start Time: 
1:30 p.m.


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. 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 reveal the linear density of states (DOS) as expected for Dirac cones. The energy and temperature dependence indicate that the topological surface states are not protected above a certain temperature and energy range, and we invoke an inelastic tunneling model involving spin excitons [2.3] that accounts for the observed behavior.

[1] W.K. Park et al., “Topological surface states interacting with bulk excitons in the Kondo insulator SmB6 revealed via planar tunneling spectroscopy” PNAS 113, 6599 (2016).
[2] W.T. Fuhrman et al., “Interaction driven subgap spin exciton in the Kondo insulator SmB6” Phys. Rev. Lett. 114, 036401 (2015).
[3] G.A. Kapilevich et al. “Incomplete protection of the surface Weyl cones of the Kondo insulator SmB6: Spin exciton scattering” Phys. Rev. B 92, 085133 (2015).

After this semi-informal talk, we may have informal discussions on any of these topics.

(PCS = Point Contact Spectroscopy; PTS = Planar Tunneling Spectroscopy)
Fe-based SCs: PCS detects DoS arising from nematicity, which is explained by orbital fluctuations.
URu2Si2:        PCS shows hybridization gap is not the hidden order, and more.
CeCoIn5:        Old PCS work first showing background is a Fano lineshape
                        Preliminary, undigested PTS work, showing a field-induced pseudogap.

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