Chiral Fermionic Valve Quantum Geometry

Scientists Create First Chiral Fermionic Valve Without Magnetism

Quantum Geometry Enables Unprecedented Control of Quantum Particles

A joint team led by Stuart Parkin at the Max Planck Institute of Microstructure Physics in Halle (Saale) and Claudia Felser at the Max Planch Institute for Chemical Physics of Solids in Dresden has unveiled a fundamentally new method for controlling quantum particles in solid materials.

Writing in Nature, the researchers describe the first experimental realization of a chiral fermionic valve—a device that spatially separates quantum particles of opposite chirality using quantum geometry alone, without the need of magnetic fields or magnetic materials.

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Breakthrough Driven by Mesoscopic Quantum Devices

The breakthrough was driven by Anvesh Dixit, a PhD student in Parkin's and the study's first author, who designed, fabricated and measured the mesoscopic devices at the heart of the discovery.

"This project was only possible because we were able to combine materials of exceptional topological quality with transport experiments operating at the mesoscopic quantum limit," Dixit said. "Observing chiral fermions separate and interfere purely as a result of quantum geometry is truly exciting."

Quantum Geometry as a New Control Principle

Chiral fermions—quantum particles defined by their handedness—play a pivotal role in topological quantum materials and hold promise for applications ranging from ultra-low-power electronics and spintronics to quantum information technologies.

Until now, however, controlling these particles has relied on strong magnetic fields or magnetic doping, severely constraining realistic device designs.

In the new study, the researchers show that quantum geometry a fundamental characteristic of electronic wavefunctions—can serve as an alternative means of control.

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How PdGa Enables Chirality Separation

High-quality single crystals of the homochiral topological semimetal PdGa, grown by Felser's team in Dresden, host multifold fermions with large and opposite Chern numbers.

When an electric current is applied, the non-trivial quantum geometry of these electronic bands produces chirality-dependent anomalous velocities.

By micro-structuring PdGa into three-arm devices, Dixit and his colleagues demonstrated that fermions of opposite chirality are steered into separate arms, while ordinary charge carriers are effectively filtered out.

"This represents an entirely new electronic function," said Stuart Parkin. "In the same way that transistors regulate charge and spin valves manipulate spin, this device enables control over fermionic chirality—a degree freedom that electronics has not previously been able to access."

Current-Induced Magnetization and Quantum Interference

The researchers showed that the separated chiral currents carry orbital magnetizations of opposite sign, generated dynamically by the electric current itself.

Crucially, these remain phase-coherent over mesoscopic distances of more than 15 micrometers.

By fabricating a Mach-Zehnder interferometer directly from PdGa, the team observed clear quantum interference of chiral currents even in the absence of any external magnetic field.

The result demonstrates coherent quantum transport of topological quasiparticles within a realistic device architecture.

"This work beautifully illustrates how quantum materials can give rise to entirely new device concepts," said Claudia Felser. "Here, quantum geometry takes the place of magnetism as the key functional element."

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Toward Chiral Quantum Electronics

The demonstrated chiral fermionic valve delivers three core functionalities:

• Spatial separation of chiral fermions into Chern-number-polarized states
• Electrical control over current-induced orbital magnetization, including its polarity
• A tunable platform that enables quantum interference of chiral quasiparticles

Because the effect operates without magnetic fields, magnetic order, or electrostatic gating, it can be applied across a broad class of homochiral and multifold topological materials.

Together, these results point towards a new era of chiral quantum electronics, in which information is encoded and processed using the handedness of quantum states.

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