Any Axion Insulator Must be a Bulk Three-Dimensional Topological Insulator

Abstract

In recent attempts to observe axion electrodynamics, much effort has focused on trilayer heterostructures of magnetic topological insulators, and in particular on the examination of a so-called zero Hall plateau, which has misguidedly been overstated as direct evidence of an axion insulator state. We investigate the general notion of axion insulators, which by definition must contain a nontrivial volume to host the axion term. We conduct a detailed magneto-transport analysis of Chern insulators comprised of a single magnetic topological insulator layer of varying thickness as well as trilayer structures, for samples optimized to yield a perfectly quantized anomalous Hall effect. Our analysis gives evidence for a topological magneto-electric effect quantized in units of e${}^2$/2h, allowing us to identify signatures of axion electrodynamics. Our observations may provide direct experimental access to electrodynamic properties of the universe beyond the traditional Maxwell equations, and challenge the hitherto proclaimed exclusive link between the observation of a zero Hall plateau and an axion insulator.

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Cited by in corpus (6)

• Routes to realize the axion-insulator phase in MnBi${}_2$Te${}_4$(Bi${}_2$Te${}_3$)${}_n$ family: a perspective
• Intrinsic magnetic topological insulators of the MnBi${}_2$Te${}_4$ family
• Observation of magnetism induced topological edge state in antiferromagnetic topological insulator MnBi4Te7
• Large-gap quantum anomalous Hall states induced by functionalizing buckled Bi-III monolayer/Al${}_2$O${}_3$
• Effects of GaAs buffer layer on quantum anomalous Hall insulator Vy(BixSb1-x)2-yTe3
• Effects of GaAs Buffer Layer on Structural, Magnetic, and Transport Properties of Magnetic Topological Insulators Cr${}_y$(Bi${}_x$Sb${}_{1-x}$)${}_{2-y}$Te${}_3$ and V${}_y$(Bi${}_x$Sb${}_{1-x}$)${}_{2-y}$Te${}_3$ Films