A chiral fermionic valve driven by quantum geometry - Nature

"Multifold topological semimetals host fermions with opposite chiralities at topological band crossings1,2,3. Chiral fermionic transport in topological systems often relies on high magnetic fields or magnetic dopants to suppress trivial transport and create an imbalance in occupancy of opposite Chern-number states4,5. Here we use the quantum geometry6,7 of topological bands to filter fermions by chirality into distinct Chern-number-polarized states. This allows for the real-space separation of currents with opposite fermionic chiralities, which we have demonstrated by observing their quantum interference in the absence of any magnetic field."

"Devices fabricated from single-crystal PdGa in a three-arm geometry exhibit quantum-geometry-induced anomalous velocities8,9 of chiral fermions, thereby exhibiting a nonlinear Hall effect. The resultant transverse chiral currents with opposite anomalous velocities are thereby spatially separated into the outer arms of the device. These chiral currents in opposing Chern number states also carry orbital magnetizations with opposite signs. The mesoscopic phase coherence of these chiral currents facilitated their quantum interference10 in a Mach-Zehnder interferometer."

Multifold topological semimetals host fermions with opposite chiralities at topological band crossings. Quantum geometry of topological bands filters fermions by chirality into distinct Chern-number–polarized states, enabling real-space separation of currents with opposite chiralities. Single-crystal PdGa devices fabricated in a three-arm geometry exhibit quantum-geometry–induced anomalous velocities of chiral fermions and a nonlinear Hall effect in zero magnetic field. Transverse chiral currents with opposite anomalous velocities populate outer device arms and carry orbital magnetizations with opposite signs. Mesoscopic phase coherence permits quantum interference of these chiral currents in a Mach–Zehnder interferometer. The system functions as a chiral fermionic valve with tunable current-induced magnetization and controllable interferometry.

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