Without Gain or Loss: Non-Hermitian Topology Emerges from Quantum Anomalous Hall Edge Transport

Non-Hermitian physics can host unusual phenomena such as exceptional points and the non-Hermitian skin effect, but most experimental realizations have relied on engineered gain, loss, or specially designed couplings to the environment. A natural question is whether a solid-state electronic system with a fully Hermitian microscopic Hamiltonian can generate non-Hermitian topology purely through its own transport dynamics. Recently, a team led by Prof. X. C. Xie at the International Center for Quantum Materials, School of Physics, Peking University, together with collaborators, answered this question affirmatively in quantum anomalous Hall (QAH) systems. They showed that the interplay between a unidirectional chiral edge channel and an ordinary diffusive edge channel produces intrinsic nonreciprocal transport and maps the edge dynamics onto the non-Hermitian Hatano–Nelson model. This mechanism yields experimentally accessible signatures of the non-Hermitian skin effect in local voltage and heat dissipation, providing a new route to non-Hermitian topology in solid-state quantum materials.

Figure 1  Chiral edge channel (blue) and ordinary edge channel (red) in the quantum anomalous Hall state, and the resulting nonreciprocal transport.

An ideal QAH insulator supports only a chiral edge channel propagating in a fixed direction, whereas realistic materials may also host ordinary edge channels with diffusive transport. When the two types of channels coexist and scatter into one another, transport becomes intrinsically directional. The researchers showed that this edge dynamics can be mapped exactly onto the continuum Hatano–Nelson model. In other words, the microscopic Hamiltonian of the sample remains Hermitian, while non-Hermiticity emerges at the level of the macroscopic transport response.

Figure 2  Spatial profiles of the electrochemical potential (voltage) and local heat dissipation along the QAH boundary, together with the length dependence of the longitudinal conductance.

The mapping leads to clear experimental signatures. In the QAH state, the local voltage develops an exponential spatial profile along the edge, and heat dissipation becomes localized in specific regions. As the sample length increases, the longitudinal conductance decays exponentially while the Hall conductance remains quantized. Numerical simulations further confirmed these predictions. By contrast, in the axion-insulator state, where the chiral edge channel is absent, these exponential features disappear. Reversing the magnetization also reverses the direction of exponential localization. Multi-terminal voltage measurements and local thermal imaging therefore provide direct ways to identify the non-Hermitian skin effect.

The study demonstrates that non-Hermitian topology does not necessarily require external gain, loss, or specially engineered devices. It can instead emerge naturally from chiral transport inside a Hermitian quantum system. By directly connecting non-Hermitian topology with mesoscopic electronic transport, this work provides a new solid-state route for exploring non-Hermitian phenomena in magnetic topological insulators and related quantum materials.

The work, entitled “Non-Hermitian Topology from Edge Transport in Hermitian Quantum Anomalous Hall Systems,” was published online in Nature Communications on 27 August 2026. Humian Zhou, a postdoctoral researcher at the International Center for Quantum Materials, Peking University, is the first author; Ming Lu from the Beijing Academy of Quantum Information Sciences is a coauthor; Prof. Chui-Zhen Chen from Soochow University and Prof. X. C. Xie from Peking University are the corresponding authors.

The work was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, the Natural Science Foundation of Jiangsu Province, and the Innovation Program for Quantum Science and Technology. The authors also acknowledge the High-performance Computing Platform of Peking University.

Website: https://doi.org/10.1038/s41467-026-77208-6