Experimental signature of the parity anomaly in a semi-magnetic topological insulator

M. Mogi, Y. Okamura, M. Kawamura, R. Yoshimi, K. Yasuda, A. Tsukazaki, K. S. Takahashi, T. Morimoto, N. Nagaosa, M. Kawasaki, Y. Takahashi, Y. Tokura

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


A three-dimensional (3D) topological insulator features a 2D surface state consisting of a single linearly dispersive Dirac cone1–3. Under broken time-reversal symmetry, the single Dirac cone is predicted to cause half-integer quantization of Hall conductance, which is a manifestation of the parity anomaly in quantum field theory1–9. However, despite various observations of quantization phenomena10–15, the half-integer quantization has not been observed because most experiments simultaneously measure a pair of equivalent Dirac cones16 on two opposing surfaces. Here we demonstrate the half-integer quantization of Hall conductance in a synthetic heterostructure termed a semi-magnetic topological insulator, where only one surface state is gapped by magnetic doping and the opposite one is non-magnetic and gapless. We observe half-quantized Faraday and Kerr rotations with terahertz magneto-optical spectroscopy and half-quantized Hall conductance in transport at zero magnetic field. Our results suggest a condensed-matter realization of the parity anomaly4–9 and open a way for studying the physics enabled by a single Dirac fermion.

Original languageEnglish
Pages (from-to)390-394
Number of pages5
JournalNature Physics
Issue number4
Publication statusPublished - 2022 Apr

ASJC Scopus subject areas

  • Physics and Astronomy(all)


Dive into the research topics of 'Experimental signature of the parity anomaly in a semi-magnetic topological insulator'. Together they form a unique fingerprint.

Cite this