Samarium hexaboride is a trivial surface conductor

Abstract

SmB6 is predicted to be the first member of the intersection of topological insulators and Kondo insulators, strongly correlated materials in which the Fermi level lies in the gap of a many-body resonance that forms by hybridization between localized and itinerant states. While robust, surface-only conductivity at low temperature and the observation of surface states at the expected high symmetry points appear to confirm this prediction, we find both surface states at the (100) surface to be topologically trivial. We find the state to appear Rashba split and explain the prominent state by a surface shift of the many-body resonance. We propose that the latter mechanism, which applies to several crystal terminations, can explain the unusual surface conductivity. While additional, as yet unobserved topological surface states cannot be excluded, our results show that a firm connection between the two material classes is still outstanding.

Comparative study of rare earth hexaborides using high resolution angle-resolved photoemission

“…Consequently, a second set of ARPES studies have argued that surface-related states may occur in these systems, possibly due to mechanisms other than topological insulator behavior, for example as a result of confinement of the bulk states in a potential generated by strong surface band bending [24,28,34] or the polarity of the cleavage surface [25].…”

“…The Kondo hybridization gap that arises from the interaction of localized f electrons and delocalized conduction carriers (d electrons) in SmB 6 was predicted to host surface states of non-trivial character [11][12][13]. This prediction gave rise to numerous transport [14][15][16][17][18], scanning tunneling microscopy/spectroscopy (STM/STS) [19][20][21] and angle-resolved photoelectron spectroscopy (ARPES) studies [22][23][24][25][26][27][28] that sought for signatures of topological characteristics in SmB 6 . At low temperatures (under 5K), various transport experiments [14,[16][17][18]29] and torque magnetometry [15] data point to the co-existence of a robust surface-related conduction channel in parallel to the bulk channel that dominates at higher temperatures.…”

Surface and electronic structure of SmB through scanning tunneling microscopy

“…the heavy quasiparticles related to the bulk and the conduction band being related to the surface states, both of which reside inside the hybridisation gap. Evidence for the former is found in specific heat [42] and recent ARPES measurements [19]. The latter may have been detected in de Haas-van Alphen experiments, which report twodimensional Fermi surfaces with light effective mass of the quasiparticles [43], a view which, however, has been challenged [35].…”

“…However, other views have also been put forward including the involvement of a surface reconstruction and of the polar nature of the (0 0 1) SmB 6 surface [17,18]. In addition, ARPES results down to 1 K have been discussed in terms of Rashba splitting [19].…”

Foreward for special issue of philosophical magazine on: topological correlated insulators and SmB6

“…As predicted, ARPES does indeed find surface states on the [1 0 0] surface at T and X , and nowhere else, and those at X are quite robust [55], even against extreme oxidation. However, the crucial Γ state (crucial because it renders the total number odd) shows great variability among data-sets and measurement surfaces [55], and some ARPES data [56] have indicated the presence of a trivial Γ Rashba surface state. If such were definitely the only Γ surface state it would immediately rule out the TI narrative.…”