Importance of Charge Fluctuations for the Topological Phase inSmB6

Abstract

Typical Kondo insulators (KIs) can have a nontrivial Z_{2} topology because the energy gap opens at the Fermi energy (E_{F}) by a hybridization between odd- and even-parity bands. SmB_{6} deviates from such KI behavior, and it has been unclear how the insulating phase occurs. Here, we demonstrate that charge fluctuations are the origin of the topological insulating phase in SmB_{6}. Our angle-resolved photoemission spectroscopy results reveal that with decreasing temperature the bottom of the d-f hybridized band at the X[over ¯] point, which is predicted to have odd parity and is required for a topological phase, gradually shifts from below to above E_{F}. We conclude that SmB_{6} is a charge-fluctuating topological insulator.

Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States

“…Among the most vivid examples are the surface states of topological insulators in which the coupling of the spin and momentum degrees of freedom gives rise to helical spin textures in momentum space [6]. Moreover, spin-orbit split band structures, in general, attract attention in a broad range of materials, including Weyl semimetals [7], with unconventional spin-polarized states in the bulk and at the surface, stronglycorrelated topological Kondo insulators [8,9], as well as twodimensional systems, such as metallic oxide interfaces [5] and transition-metal dichalcogenide layers [3]. Thus, given the tremendous interest in spin-orbit coupled materials, it is of critical importance to probe their electronic structure with spin sensitivity and to reliably verify the anticipated spin dependences, see, e.g., Refs.…”

Topological surface states interacting with bulk excitations in the Kondo insulator SmB 6 revealed via planar tunneling spectroscopy

“…In particular, samarium hexaboride (SmB 6 ) has drawn great attention owing to its telltale resistivity behavior saturating below 4 K (5). Various experiments have been implemented to investigate this possibility (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24), establishing the robustness of the surface states and the Kondo hybridization leading to a formation of the bulk gap, but their topological origin and nature has not been unambiguously confirmed. Factors contributing to this situation include their inherently complex nature due to strong correlations, nontrivial surface chemistry, and insufficient energy resolution.…”

Two-component analysis of the 4f multiplet of samarium hexaboride

“…For instance, localized 4f states with odd parity are forming hybridization gaps with the conduction band at the Fermi 5 energy, possibly resulting in physical phases with non-trivial Z 2 topology [5,6] and thereby giving rise to quantum spin Hall states in strongly correlated materials [3]. However, the hybridized nature of the 4f states can cause difficulties in estimating the Z 2 topological indices because the hybridization may induce an odd-parity character even in the electronic states predominantly assigned 10 to the other elements [7]. When the 4f states are occupied with more that one single electron (or hole), the experimental investigation by photoemission spectroscopy is usually difficult because the spectral signatures of the 4f states appear as complicated final state multiplets [8].…”

“…Recently, samarium hexaboride (SmB 6 ) has drawn much attention because it exemplifies a strongly correlated system with non-trivial Z 2 topology [7, 9,10,11]. Its resistivity below 5 K was found to be temperature-independent, which cannot be explained by the impurity scattering mechanisms in a classical metal [12,13] and which has been interpreted as a signature of topological 20 surface states [14,15].…”

“…gives rise to a complex thermal evolution in the electronic structure accompanied by an energy shift and a redistribution of spectral weight near E F [10,18,26].…”