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

Ke-Jun Xu; Su-Di Chen; Yu He; Junfeng He; Shujie Tang; Chunjing Jia; Eric Yue Ma; Sung-Kwan Mo; Donghui Lu; Makoto Hashimoto; Thomas P Devereaux; Zhi-Xun Shen

doi:10.1073/pnas.2002361117

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

Proc Natl Acad Sci U S A. 2020 Jul 7;117(27):15409-15413. doi: 10.1073/pnas.2002361117. Epub 2020 Jun 22.

Authors

Ke-Jun Xu^{1

2

3}, Su-Di Chen^{1

2

3}, Yu He^{1

2

3}, Junfeng He^{1

2}, Shujie Tang^{1

2

4}, Chunjing Jia¹, Eric Yue Ma^{2

3}, Sung-Kwan Mo⁴, Donghui Lu⁵, Makoto Hashimoto⁵, Thomas P Devereaux^{1

2

6}, Zhi-Xun Shen^{7

2

3

8}

Affiliations

¹ Stanford Institute for Materials and Energy Sciences, Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory, Menlo Park, CA 94025.
² Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305.
³ Department of Applied Physics, Stanford University, Stanford, CA 94305.
⁴ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
⁵ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025.
⁶ Department of Material Science and Engineering, Stanford University, Stanford, CA 94305.
⁷ Stanford Institute for Materials and Energy Sciences, Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory, Menlo Park, CA 94025; zxshen@stanford.edu.
⁸ Department of Physics, Stanford University, Stanford, CA 94305.

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.

Keywords: angle-resolved photoemission spectroscopy; correlated materials; quantum materials; topological materials.