Importance of Charge Fluctuations for the Topological Phase in SmB6

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. SmB6 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 SmB6. Our angle-resolved photoemission spectroscopy results reveal that with decreasing temperature the bottom of the d-f hybridized band at the (X) over bar 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 SmB6 is a charge-fluctuating topological insulator.