Loss of Hall conductivity quantization in a non-Hermitian quantum anomalous Hall insulator

Timothy M. Philip, Mark R. Hirsbrunner, Matthew J. Gilbert

Research output: Contribution to journalArticlepeer-review


Recent work has extended topological band theory to open, non-Hermitian Hamiltonians, yet little is understood about how non-Hermiticity alters the topological quantization of associated observables. We address this problem by studying the quantum anomalous Hall effect (QAHE) generated in the Dirac surface states of a three-dimensional time-reversal-invariant topological insulator (TI) that is proximity coupled to a metallic ferromagnet. By constructing a contact self-energy for the ferromagnet, we show that in addition to generating a mass gap in the surface spectrum, the ferromagnet can introduce a non-Hermitian broadening term, which can obscure the mass gap in the spectral function. We calculate the Hall conductivity for the effective non-Hermitian Hamiltonian describing the heterostructure and show that it is no longer quantized despite being classified as a Chern insulator based on non-Hermitian topological band theory. Our results indicate that the QAHE will be challenging to experimentally observe in ferromagnet-TI heterostructures due to the finite lifetime of quasiparticles at the interface.

Original languageEnglish (US)
Article number155430
JournalPhysical Review B
Issue number15
StatePublished - Oct 22 2018
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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