Evidence for in-gap surface states on the single phase SmB6(001) surface

Abstract

Structural and electronic properties of the SmB6(001) single-crystal surface prepared by Ar+ ion sputtering and controlled annealing are investigated by scanning tunneling microscopy. In contrast to the cases of cleaved surfaces, we observe a single phase surface with a non-reconstructed p(1 × 1) lattice on the entire surface at an optimized annealing temperature. The surface is identified as Sm-terminated on the basis of spectroscopic measurements. On a structurally uniform surface, the emergence of the in-gap state, a robust surface state against structural variation, is further confirmed inside a Kondo hybridization gap at 4.4 K by temperature and atomically-resolved spatial dependences of the differential conductance spectrum near the Fermi energy.

Topological nonmagnetic impurity states in topological Kondo insulators

“…The bulk component of the resistivity is thermally activated and increases by ten orders of magnitude [15], indicating that the bulk is an exceptionally good insulator and that the surface is metallic. Surface states have also been observed in ARPES [16,17,18] and tunneling spectroscopies [19,20,21,22,23,24], which provides further evidence that is consistent with SmB 6 being topological. However, 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 topological.…”

Comparative Scanning Tunneling Microscopy Study on Hexaborides

“…Upon searching, a surface reconstruction can usually be found. [ 28,30,39 ] The reconstruction was also observed by low‐energy electron diffraction, [ 36,40,41 ] as well as by STM on LaB 6 . [ 42 ] Clearly, if we assume that the reconstruction results from each second row of Sm atoms missing on top of an otherwise B‐terminated surface, such a reconstruction is energetically favorable compared with an unreconstructed polar surface.…”

“…[ 28 ] The orange spectrum attained on the elevated part of the topography in Figure 3 shows a well‐developed hump at mV. [ 27,28,41 ] It is tempting to compare this hump with the conspicuous maximum observed on Sm‐terminated surfaces of larger areas. [ 27,28 ] Note that we did not observe (Figure 4 and the study by Rößler et al [ 28 ] ) a pronounced shift in energy of features at negative V as reported in previous studies.…”

Non-trivial surface states of samarium hexaboride at the (111) surface

“…Although the metallic surface states dispersed across the bulk Kondo gap were discovered in TKI, as predicted 9–13 , a subsequent high-resolution ARPES study made a counter-claim regarding such TKI assignment by stating that some of the metallic surface states do not disperse continuously across the bulk Kondo gap but accidentally lie at the Fermi level ( E F ) 14 . Although numerous other studies such as surface-transport 15 and scanning tunnelling microscopy 16,17 strongly suggest the topologically non-trivial nature of SmB 6 , the detailed surface electronic and spin texture of SmB 6 have remained unclear because of this disagreement. Moreover, a peculiar Fermi surface behaviour of SmB 6 has been reported recently through the de Haas–van Alphen (dHvA) measurements 18–21 .…”