Effects of spin excitons on the surface states of SmB6 : A photoemission study

Abstract

We present the results of high-resolution valence-band photoemission spectroscopic study of SmB6 which shows evidence for a V-shaped density of states of surface origin within the bulk gap. The spectroscopy data is interpreted in terms of the existence of heavy 4f surface states, which may be useful in resolving the controversy concerning the disparate surface Fermi-surface velocities observed in experiments. Most importantly, we 1 find that the temperature dependence of the valence-band spectrum indicates that a small feature appears at a binding energy of about -9 meV at low temperatures. We attribute this feature to a resonance caused by the spin-exciton scattering in SmB6 which destroys the protection of surface states due to time-reversal invariance and spin-momentum locking. The existence of a low-energy spin-exciton may be responsible for the scattering which suppresses the formation of coherent surface quasi-particles and the appearance of the saturation of the resistivity to temperatures much lower than the coherence temperature associated with the opening of the bulk gap.

An STM Perspective on Hexaborides: Surface States of the Kondo Insulator SmB6

“…[128]. The hybridization gap obtained ranged between 14–20 meV, [ 127,128,140,165,167 ] in line with results of other measurements, [ 16–18,20,21,134,155,166,177–179 ] albeit smaller gaps were also reported. [ 23,122,123 ] The observation of co‐tunneling phenomena also on reconstructed [ 126 ] or less well‐defined surfaces is consistent with the bulk nature of the underlying Kondo effect.…”

Samarium hexaboride is a trivial surface conductor

“…Although small, the 10 meV surface shift we find for B termination is crucial, because it still considerably exceeds the ~3.5 meV activation energy found in transport measurements 6 , 24 , 25 . This activation energy is often attributed to (as yet unidentified) states inside a wider 15–20 meV bulk hybridization gap 26 , 27 , and photoemission results are generally regarded to support this notion of a large bulk gap. As we will see shortly, however, the results depend strongly on the sample termination in this regard as well.…”

Topological Impurity States in Three-dimensional Topological Kondo Insulators?

“…Despite a number of experimental efforts by various groups, no direct evidence has been obtained which conclusively proves that SmB 6 has a non-trivial gauge topology. The properties of SmB 6 are not well-understood, probably partially due to the strong electronic correlations [6][7][8][9][10][11][12][13] and probably due to the presence of impurities [14][15][16][17][18][19]. In this article, we show that Kondo Insulators support two-types of impurity states, and that the in-gap states could be topologically non-trivial.…”