Realization of the Axion Insulator State in Quantum Anomalous Hall Sandwich Heterostructures

Editors' Suggestion

Realization of the Axion Insulator State in Quantum Anomalous Hall Sandwich Heterostructures

Di Xiao, Jue Jiang, Jae-Ho Shin, Wenbo Wang, Fei Wang, Yi-Fan Zhao, Chaoxing Liu, Weida Wu, Moses H. W. Chan, Nitin Samarth, and Cui-Zu Chang

Phys. Rev. Lett. 120, 056801 – Published 31 January 2018

Abstract

The “magnetoelectric effect” arises from the coupling between magnetic and electric properties in materials. The $Z_{2}$ invariant of topological insulators (TIs) leads to a quantized version of this phenomenon, known as the topological magnetoelectric (TME) effect. This effect can be realized in a new topological phase called an “axion insulator” whose surface states are all gapped but the interior still obeys time reversal symmetry. We demonstrate such a phase using electrical transport measurements in a quantum anomalous Hall (QAH) sandwich heterostructure, in which two compositionally different magnetic TI layers are separated by an undoped TI layer. Magnetic force microscopy images of the same sample reveal sequential magnetization reversals of the top and bottom layers at different coercive fields, a consequence of the weak interlayer exchange coupling due to the spacer. When the magnetization is antiparallel, both the Hall resistance and Hall conductance show zero plateaus, accompanied by a large longitudinal resistance and vanishing longitudinal conductance, indicating the realization of an axion insulator state. Our findings thus show evidence for a phase of matter distinct from the established QAH state and provide a promising platform for the realization of the TME effect.

Received 1 October 2017
Revised 28 November 2017

DOI:https://doi.org/10.1103/PhysRevLett.120.056801

Physics Subject Headings (PhySH)

Quantum anomalous Hall effect

Heterostructures Thin films Topological insulators

Dilution refrigerator Magnetic force microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Di Xiao¹, Jue Jiang¹, Jae-Ho Shin¹, Wenbo Wang², Fei Wang¹, Yi-Fan Zhao¹, Chaoxing Liu¹, Weida Wu², Moses H. W. Chan^1,*, Nitin Samarth^1,†, and Cui-Zu Chang^1,‡

¹Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
²Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA

^*Corresponding author. mhc2@psu.edu
^†Corresponding author. nxs16@psu.edu
^‡Corresponding author. cxc955@psu.edu

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 120, Iss. 5 — 2 February 2018

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
V-doped ${(Bi, Sb)}_{2} {Te}_{3} / TI / Cr$ -doped ${(Bi, Sb)}_{2} {Te}_{3}$ sandwich heterostructure. (a) Signatures of the QAH insulator states in individual Cr- and V-doped ${(Bi, Sb)}_{2} {Te}_{3}$ films measured at $T = 30 mK$ . The $H_{c}$ of the V-doped QAH film $H_{c 1} \sim 1.06 T$ ; the $H_{c}$ of the Cr-doped QAH film $H_{c 2} \sim 0.14 T$ . (b) Schematic drawing and cross-sectional TEM image of a QAH sandwich heterostructure. (c) Schematics of a sandwich heterostructure with parallel magnetization alignment surfaces, supporting a 1D chiral edge state. (d) Schematics of a sandwich heterostructure with antiparallel magnetization alignment surfaces, supporting an axion insulator state.
Reuse & Permissions
Figure 2
Signature of an axion insulator in a 3-5-3 SH1 with antiparallel magnetization alignment. (a, b) $μ_{0} H$ dependence of $σ_{x x}$ and $σ_{x y}$ of 3-5-3 SH1 at $V_{g} = V_{g}^{0}$ and $T = 30 mK$ . An axion insulator is observed if the zero $σ_{x y}$ plateau region is the consequence of antiparallel magnetization alignment. The red and blue lines are guides to the eye. (c) Flow diagram of ( $σ_{x y}$ , $σ_{x x}$ ) of the 3-5-3 SH1 from $μ_{0} H = 1.8$ to $μ_{0} H = - 1.8 T$ [the red curves in (a) and (b)]. Two semicircles of radius $0.5 h / e^{2}$ centered at ( $0.5 h / e^{2}$ , 0) and ( $- 0.5 h / e^{2}$ , 0) are shown in dashed lines. (d) Flow diagram of ( $σ_{x y}^{b}$ , $σ_{x x}^{b}$ ) of the bottom surface from $μ_{0} H = 1.8$ to $μ_{0} H = - 0.45 T$ . (e) Flow diagram of ( $σ_{x y}^{t}$ , $σ_{x x}^{t}$ ) of the top surface from $μ_{0} H = - 0.45$ to $μ_{0} H = - 1.8 T$ . A semicircle of radius $0.5 h / e^{2}$ centered at (0, 0) is shown in a dashed line in (d) and (e). Here $μ_{0} H = - 0.45 T$ is chosen to separately study the scalings of the top and bottom surfaces of the QAH sandwich heterostructures in proper magnetic field sweeping regions.
Reuse & Permissions
Figure 3
Two-step magnetization reversal in the 3-5-3 SH2. (a) $μ_{0} H$ dependence of $ρ_{x y}$ of 3-5-3 SH2 at $V_{g} = 0 V$ and $T = 5.3 K$ . (b) $μ_{0} H$ dependence of magnetic domain contrasts ( $δ f$ ) at $V_{g} = 0$ and $T = 5.3 K$ . The $δ f$ is estimated from the rms value of MFM images in (c)–(j). (c)–(j)The MFM images at various $μ_{0} H s$ . Red and blue represent respectively upward and downward parallel magnetization alignment regions, green represents antiparallel magnetization alignment regions. The Hall traces in (a) and the MFM images in (c)–(j)are measured simultaneously. (k) $μ_{0} H$ dependence of $ρ_{y x}$ at various temperatures. $ρ_{y x}$ exhibits two-step transition when $T < 10 K$ . (l), (m) Minor loops of the $ρ_{y x}$ at $V_{g} = V_{g}^{0}$ and $T = 30 mK$ (l) and at $V_{g} = 0 V$ , and $T = 5.3 K$ (m).
Reuse & Permissions
Figure 4
Gate tuning of $ρ_{x x}$ , $ρ_{y x}$ , and $σ_{x y}$ of the 3-5-3 SH1 at $T = 30 mK$ . (a)–(e) $μ_{0} H$ dependence of $ρ_{x x}$ (top panels), $ρ_{y x}$ (middle panels), and $σ_{x y}$ (bottom panels) at varied $V_{g} s$ . The red and blue curves show results sweeping $μ_{0} H$ downward and upward, respectively.
Reuse & Permissions

Physical Review Letters