"Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb2"

Ke-Jun Xu: Su-Di Chen, Yu He, View ORCID ProfileJunfeng He, Shujie Tang, Chunjing Jia, View ORCID ProfileEric Yue Ma, View ORCID ProfileSung-Kwan Mo, Donghui Lu, Makoto Hashimoto, View ORCID ProfileThomas P. Devereaux, and Zhi-Xun Shen; Proceedings of the Nationa Academy of Sciences, 06/22/20.

Additional Authors: Su-Di Chen, Yu He, View ORCID ProfileJunfeng He, Shujie Tang, Chunjing Jia, View ORCID ProfileEric Yue Ma, View ORCID ProfileSung-Kwan Mo, Donghui Lu, Makoto Hashimoto, View ORCID ProfileThomas P. Devereaux, and Zhi-Xun Shen

Abstract:

The resistance of a conventional insulator diverges as temperature approaches zero. The peculiar low-temperature resistivity saturation in the 4f Kondo insulator (KI) SmB6 has spurred proposals of a correlation-driven topological Kondo insulator (TKI) with exotic ground states. However, the scarcity of model TKI material families leaves difficulties in disentangling key ingredients from irrelevant details. Here we use angle-resolved photoemission spectroscopy (ARPES) to study FeSb2, a correlated d-electron KI candidate that also exhibits a low-temperature resistivity saturation. On the (010) surface, we find a rich assemblage of metallic states with two-dimensional dispersion. Measurements of the bulk band structure reveal band renormalization, a large temperature-dependent band shift, and flat spectral features along certain high-symmetry directions, providing spectroscopic evidence for strong correlations. Our observations suggest that exotic insulating states resembling those in SmB6 and YbB12 may also exist in systems with d instead of f electrons.