Half-Quantized Chiral Edge Current in a Parity Anomaly State
Phys. Rev. Lett. 136, 016601 – Published 2 January, 2026
DOI: https://doi.org/10.1103/vxcb-rwbl
Abstract
A single massive Dirac surface band is predicted to exhibit a half-quantized Hall conductance, a hallmark of the parity anomaly state in quantum field theory. Experimental signatures of the parity anomaly state have been observed in semimagnetic topological insulator (TI) bilayers, yet whether it supports a half-quantized chiral edge current remains elusive. Here, we observe a robust half-quantized Hall conductance plateau in a molecular beam epitaxy grown asymmetric magnetic TI trilayer under specific in plane magnetic field regimes, corresponding to the parity anomaly state. Within this state, both nonlocal and nonreciprocal transport signals are greatly enhanced, which we identify as direct evidence for a half-quantized chiral edge current localized at the boundary of the top gapped surface. Our numerical simulations demonstrate that this half-quantized chiral edge channel is the essential carrier of the observed half-quantized Hall conductance plateau. The half-quantized chiral edge channel emerges from the collective behavior of multiple metallic modes of massless Dirac electrons and is fundamentally distinct from the fully quantized chiral edge channel in the quantum anomalous Hall state. Our results provide experimental evidence for the half-quantized chiral edge transport in a parity anomaly state. This Letter establishes asymmetric magnetic TI trilayers as a platform for probing single Dirac fermion physics and paves the way to explore a series of exciting phenomena in the parity anomaly state, including the topological magnetoelectric effect and quantized magneto-optical response.
