Direct measurement of a remnant Fermi surface in SmB6

Visualizing the atomic-scale origin of metallic behavior in Kondo insulators

“…First, the detection of de Haas-van Alphen (magnetic) oscillations without accompanying Shubnikov-de Haas (resistiv-ity) oscillations (8-10) is expected for electrically isolated metallic puddles, provided that they do not meet the percolation threshold [which could be unreachable (17)]. Second, the large Fermi surface size and light effective mass extracted by bulk probes (9)(10)(11) is in excellent agreement with our observation of itinerant 5d electrons. Third, the magnetic length of the high-frequency (large-k F ) quantum oscillations that onset above 35 T (9, 10) is com-parable to the R(r) decay length of g = 2.6 nm, such that a Landau orbit could fit inside a metallic puddle.…”

“…Third, the magnetic length of the high-frequency (large-k F ) quantum oscillations that onset above 35 T (9, 10) is com-parable to the R(r) decay length of g = 2.6 nm, such that a Landau orbit could fit inside a metallic puddle. Additionally, many of the metallic properties were detected in floating zone-grown samples (5,6,(9)(10)(11), which are known to have higher concentrations of Sm vacancies than samples grown with an aluminum flux (60). Floating-zone samples also contain a higher concentration of dislocations (31), which may similarly disrupt the Kondo screening cloud and thus further enhance the quantum oscillation amplitude beyond that expected from Sm vacancies alone.…”

“…For example, the topological Kondo insulator samarium hexaboride (SmB 6 ) displays a sizable bulk optical conductivity at terahertz frequencies (5) and a finite electronic specific heat at low temperatures (6)(7)(8)(9). A complete three-dimensional (3D) Fermi surface matching its high-temperature metallic state was reconstructed from quantum oscillation (9,10) and Compton scattering (11) measurements performed in the insulating regime. Notably, these metallic properties persist even as the bulk resistivity of SmB 6 increases by 10 orders of magnitude (12).…”

Breakdown of bulk-projected isotropy in surface electronic states of topological Kondo insulator SmB$_6$(001)

“…From this anisotropy, the other electronic properties, such as the electron conductivity, are also suggested to be anisotropic on SmB 6 (001)-p(2×2), as far as they are derived from the TSS. Therefore, examining the rotation asymmetry from the vicinal SmB 6 (001) sample with insitu surface preparation would be an interesting new pathway to distinguish the origin and dimensionality (2D or 3D) of unconventional electronic phenomena observed in SmB 6 , such as the thermodynamic properties [32] and quantum oscillations [22][23][24][25][26][27].…”

“…This result emphasizes the important role of the surface atomic structure even in the TSS. We also discuss that the characteristic anisotropy of the SmB 6 (001) surface states could provide a new pathway to survey the peculiar Fermi surface without electric conduction observed in the small Kondo gap of SmB 6 [22][23][24][25][26][27], whose origin, from the 3D bulk or 2D surface, is still controversial.…”