This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers at Tohoku University and the Japan Atomic Energy Agency (JAEA) have successfully controlled a unique quantum phenomenon—the quantum-geometric nonlinear Hall (QgNLH) state—using electric current for the first time. The breakthrough was achieved by revealing and exploiting the coupling between the spin structure and the QgNLH state in an electrically switchable chiral antiferromagnet.
The achievements, published in the journal Newton on Nov. 4, 2026, offer a potential approach for developing electrically tunable devices that use quantum-geometric effects to perform nonlinear signal processing functions. Electrical conduction underpins modern electronics. In an ordinary conductor, the voltage and the current are proportional, as described by Ohm's law and the Hall effect.
In some materials, however, these linear laws can be violated. A typical example is the nonlinear Hall effect, in which the Hall voltage appearing in the transverse direction of the current no longer follows the usual linear relationship. Quantum geometry—the geometric structure of electronic quantum states—plays a crucial role in producing such an unconventional nonlinear voltage-current response.
The corresponding quantum-geometric nonlinear Hall (QgNLH) state is therefore of interest both as a way to explore the quantum properties of solids and as a new basis for nonlinear signal processing. For practical electronic devices, however, it is necessary not only to observe this response but also to control it by electric current. This has remained challenging because the quantum geometry has been interpreted as a built-in property of the material.
The research team investigated epitaxial thin films of the chiral antiferromagnet Mn₃Sn. Its spin structure is closely connected to its electronic states, making Mn₃Sn a promising material to explore how the control of magnetic properties can be used to manipulate the unconventional responses from quantum geometry. They first observed a third-order nonlinear Hall effect at room temperature, i.e., the nonlinear voltage is proportional to the cube of the current.
Combining experiments with theoretical calculations, they verified that the observed effect has a quantum-geometric origin and is reversible by switching the spin structure of Mn₃Sn, hence revealing the interplay between the QgNLH state and the spin structure. The team subsequently used spintronic approaches to electrically control the magnetic order and the associated QgNLH state. When an electric current flows in a heavy metal layer adjacent to Mn₃Sn, the resulting spin-orbit torque acts on the spin structure of Mn₃Sn and is capable of switching it.
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