Robust Surface States and Coherence Phenomena in Magnetically AlloyedSmB6

Abstract

Samarium hexaboride is a candidate for the topological Kondo insulator state, in which Kondo coherence is predicted to give rise to an insulating gap spanned by topological surface states. Here we investigate the surface and bulk electronic properties of magnetically alloyed Sm 1-x M x B 6 (M=Ce, Eu). Remarkably, in-gap surface states visible to angle-resolved photoemission spectroscopy (ARPES) and resistivity features associated with Kondo coherence are both found to persist in highly modified samples with up to 30% Sm substitution. The results are interpreted in terms of a hierarchy of energy scales, in which surface state emergence is linked to the relatively robust formation of a direct Kondo gap.

Crystal Growth by the Floating Zone Method of Ce-Substituted Crystals of the Topological Kondo Insulator SmB6

“…In contrast to the saturation plateau seen in the resistivity of SmB 6 at lowest temperatures, ρ (T) for the Sm 1−x Ce x B 6 samples increases monotonically with decreasing temperature below 10 K. These results are in agreement with the transport measurements performed on aluminium flux grown Ce-substituted SmB 6 single crystals [54]. There is an evolution from the TKI behaviour of pure SmB 6 to a dense Kondo system with low temperature spin ordering of CeB 6 [7,8,75].…”

“…The effective moment, µ eff , per formula unit at 300 K varies from 2.4(1)µ B for x = 0.00 to 2.5(1)µ B for x = 0.20. The form of χ (T) for the Sm 1−x Ce x B 6 crystals is qualitatively similar than data reported for aluminium flux grown Ce-substituted SmB 6 single crystals, although the effective moments in our samples are substantially lower, especially for lower Ce concentrations [54]. The χ (T) data are consistent with magnetic response expected for a mixture of 4 f 1 Ce 3+ ions 2.54µ B /Ce 3+ and divalent and trivalent Sm ions in a variety of magnetic and nonmagnetic electronic configurations, 4 f 6 , 4 f 5 d 1 , and 4 f 5 [68,73,74].…”

“…One route towards the investigation of the exotic metallic surface state arising in SmB 6 and understanding of its topological nature, is through chemical substitution in this TKI with other rare earth ions. Recently, studies have been carried out on Eu, Gd, La, Y and Yb-substituted SmB 6 [18,21,[49][50][51][52][53][54]. High levels of substitution of non-magnetic ions (above 30%), and substitutions with small amounts of magnetic ions, were found to destroy the saturation seen in the low temperature resistivity of pure SmB 6 .…”

“…In the present work, we investigated single crystals of Sm 1−x Ce x B 6 , with a focus on studying the effects that the substitution of the magnetic Ce ion have on the structural and physical properties of SmB 6 . The physical properties of Ce-substituted SmB 6 samples have previously been investigated; however, this has only been done on polycrystalline samples and flux grown crystals [21,49,54]. Crystals of pure cerium and samarium hexaboride have previously been grown using the floating zone (FZ) technique [55][56][57]; however, Ce-substituted SmB 6 compounds have only been grown in crystal form using the flux method [54].…”

“…The physical properties of Ce-substituted SmB 6 samples have previously been investigated; however, this has only been done on polycrystalline samples and flux grown crystals [21,49,54]. Crystals of pure cerium and samarium hexaboride have previously been grown using the floating zone (FZ) technique [55][56][57]; however, Ce-substituted SmB 6 compounds have only been grown in crystal form using the flux method [54]. SmB 6 crystals grown using Al flux could suffer from contamination by the flux affecting some of the physical properties of the crystals, thereby making it difficult to study the intrinsic properties of pure samarium hexaboride [58].…”