Signature of band inversion in the antiferromagnetic phase of axion insulator candidate ${\mathrm{EuIn}}_{2}{\mathrm{As}}_{2}$

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Signature of band inversion in the antiferromagnetic phase of axion insulator candidate ${EuIn}_{2} {As}_{2}$

Takafumi Sato, Zhiwei Wang, Daichi Takane, Seigo Souma, Chaoxi Cui, Yongkai Li, Kosuke Nakayama, Tappei Kawakami, Yuya Kubota, Cephise Cacho, Timur K. Kim, Arian Arab, Vladimir N. Strocov, Yugui Yao, and Takashi Takahashi

Phys. Rev. Research 2, 033342 – Published 1 September 2020

Abstract

We have performed angle-resolved photoemission spectroscopy on ${EuIn}_{2} {As}_{2}$ which is predicted to be an axion insulator in the antiferromagnetic state. By utilizing soft-x-ray and vacuum-ultraviolet photons, we revealed a three-dimensional hole pocket centered at the $Γ$ point of the bulk Brillouin zone together with a heavily hole-doped surface state in the paramagnetic phase. Upon entering the antiferromagnetic phase, the band structure exhibits a marked reconstruction characterized by the emergence of an “M”-shaped bulk band near the Fermi level. The qualitative agreement with first-principles band-structure calculations suggests the occurrence of bulk-band inversion at the $Γ$ point in the antiferromagnetic phase. We suggest that ${EuIn}_{2} {As}_{2}$ provides a good opportunity to study the exotic quantum phases associated with a possible axion-insulator phase.

Received 22 February 2020
Accepted 2 July 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.033342

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Fermi surface Surface states

Topological insulators

Density functional theory Photoemission spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Takafumi Sato ^1,2,3,*, Zhiwei Wang^4,*, Daichi Takane¹, Seigo Souma ^2,3, Chaoxi Cui⁴, Yongkai Li⁴, Kosuke Nakayama ^1,5, Tappei Kawakami¹, Yuya Kubota¹, Cephise Cacho⁶, Timur K. Kim ⁶, Arian Arab⁷, Vladimir N. Strocov⁷, Yugui Yao^4,†, and Takashi Takahashi^1,2,3,‡

¹Department of Physics, Tohoku University, Sendai 980-8578, Japan
²Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
³WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
⁴Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (Ministry of Education), Beijing Key Lab of Nanophotonics, and Ultrafine Optoelectronic Systems, and School of Physics, Beijing Institute of Technology, 100081 Beijing, China
⁵Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), Tokyo 102-0076, Japan
⁶Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0QX, United Kingdom
⁷Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland

^*These authors contributed equally to this work.
^†Corresponding author: ygyao@bit.edu.cn
^‡Corresponding author: t.takahashi@arpes.phys.tohoku.ac.jp

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Vol. 2, Iss. 3 — September - November 2020

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Figure 1
(a) Crystal structure of ${EuIn}_{2} {As}_{2}$ . (b) Bulk hexagonal BZ and corresponding surface BZ. (c) Energy distribution curve (EDC) in a wide $E_{B}$ region measured with $h ν = 90$ eV in the PM phase ( $T = 30$ K). Inset shows the near- $E_{F}$ EDC measured with $h ν = 427$ eV. (d) ARPES-intensity mapping at $E_{F}$ as a function of in-plane wave vectors ( $k_{x}$ and $k_{y}$ ) at $k_{z} \sim 0$ ( $h ν = 427$ eV) measured at $T = 30$ K. (e) ARPES-intensity mapping at $E_{F}$ as a function of $k_{∥}$ and $k_{z}$ measured with $h ν = 360$ –480 eV at $T = 30$ K, highlighting the bulk holelike Fermi surface centered at $Γ$ (dashed rectangle). (f)–(h) ARPES intensity as a function of $k_{∥}$ and $E_{B}$ measured along cuts A–C in (e), respectively.
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Figure 2
(a) ARPES-intensity mapping at $E_{F}$ as a function of in-plane wave vectors measured with VUV photons ( $h ν = 90$ eV) at $T = 35$ K. The dashed circle shows the bulk FS at the $k_{z} = 0$ plane determined with SX photons [see Fig. 1]. (b) ARPES-intensity mapping at $E_{F}$ as a function of $k_{∥}$ and $k_{z}$ measured with $h ν = 20$ –40 eV at $T = 35$ K. The dashed curve shows the bulk FS determined with SX photons [see Fig. 1]. (c) ARPES intensity as a function of $k_{∥}$ and $E_{B}$ measured along cuts A–D in (b).
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Figure 3
(a), (b) ARPES intensities as a function of $k_{∥}$ and $E_{B}$ at $k_{z} \sim 0$ ( $h ν$ = 31 eV) and $k_{z} \sim π$ ( $h ν = 27$ eV), respectively, measured at $T = 35$ K. The EDC at point D is also plotted by the light blue curve in (b) to show the existence of a Fermi edge supporting the $E_{F}$ crossing of the weak holelike feature. (c), (d) Same as (a) and (b), respectively, but measured at $T = 6$ K. (e), (f) Band structures obtained from first-principles band-structure calculations for the $AFM ∥ b$ state [see inset to (f)], for $k_{z} = 0$ and $π$ , respectively. (g), (h) Same as (e) and (f) but for the $AFM ∥ c$ state. (i) EDCs at $T = 6$ and 35 K measured at three representative $k$ points (A–C) indicated by white solid lines in (c). The EDC at $T = 6$ K magnified around $E_{F}$ at point B is shown in the inset. (j) Schematic band picture in the AFM phase for bulk In $5 s$ , As $4 p$ states and SS deduced from the present ARPES experiment.
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Figure 4
Magnetic field dependence of $ρ_{y x}$ at $T = 2$ K (black) and 300 K (red).
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Figure 5
(a) Surface hexagonal BZ of ${EuIn}_{2} {As}_{2}$ and a $k$ cut (red line) where the calculation was performed. (b), (c) Calculated ARPES intensity profiles along the $\bar{Γ} \bar{M}$ cut for the Eu-terminated surface in the $AFM ∥ b$ and $AFM ∥ c$ phases, respectively. (d), (e) Same as (b) and (c), respectively, but for the As-terminated surface.
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Physical Review Research

Signature of band inversion in the antiferromagnetic phase of axion insulator candidate EuIn2As2

Takafumi Sato, Zhiwei Wang, Daichi Takane, Seigo Souma, Chaoxi Cui, Yongkai Li, Kosuke Nakayama, Tappei Kawakami, Yuya Kubota, Cephise Cacho, Timur K. Kim, Arian Arab, Vladimir N. Strocov, Yugui Yao, and Takashi Takahashi

Phys. Rev. Research 2, 033342 – Published 1 September 2020

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Signature of band inversion in the antiferromagnetic phase of axion insulator candidate ${EuIn}_{2} {As}_{2}$