Metallic chemical potentials in an insulating topological state

Abstract

Controlling the density of electrons inside an insulator via the chemical potential is a cornerstone of modern electronics, enabling the electrical conductivity of semiconductors and the emergence of fascinating new properties linked with electronic correlations. The compound SmB6 has drawn widespread attention in recent years as the first insulator to feature both strong electronic correlations and topological quantum order1-7, potentially enabling a host of new phenomenologies as charge density is modified. However, chemical potential has not been experimentally controlled in studies to date of the electronic structure. Here we present an angle-resolved photoemission spectromicroscopy (μ-ARPES) study of SmB6 alloys, using the natural inhomogeneity of sample surfaces to create the analogue of a multi-dimensional doping series. The role of electronic correlations is observed in the interplay of the topologically ordered conducting states with one another and with the chemical potential. Higher doping is found to result in the transformation of these interdependencies as the disorder from impurities erodes quantum coherence. These findings set the stage for a holistic understanding of the interplay between strong correlations and topological features in the electron system. Moreover, they validate recent analyses suggesting that the electronic structure of SmB6 can present the key hallmarks of conventional electron doping, such as a Fermi surface, while nonetheless preserving long-range insulating character in electrical transport measurements8-10.

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

“…S2), implying that the charge density at position r can usually be inferred by measuring trueε˜fboldnormalr. In fact, the linear dependence of trueε˜fboldnormalr on n c ( r ) was recently verified experimentally by micrometer-scale angle-resolved photoemission spectroscopy (ARPES) measurements in Eu-doped SmB 6 ( 42 ).…”

Recent progress in clean-surface formation of topological Kondo insulators and topological surface states observed there

“…One possible approach to solve this problem is to use ARPES with high spatial resolution [61], which can pick up the surface bands in only one surface domain. However, the available data reported so far are limited to an order of 10 μm [62]. While such ARPES microscopy provides valuable data, this spatial scale is not enough to resolve a complex mosaic of surface domains on SmB 6 (001), as shown in figure 6.…”