Origin of the asymmetric training behavior at fractional filling

Determine the origin of the training asymmetry in the zero-field Chern-insulating state at moiré filling factor ν=1/2, including whether twist-angle inhomogeneity causes the asymmetry.

Background

At ν=1/2, the Hall-resistance hysteresis loop is well quantized when the device is trained at positive out-of-plane magnetic field but not when trained at negative field. The authors report that the physical origin of this asymmetry has not been established and suggest twist-angle inhomogeneity as one possible explanation.

References

The loop at ν=1/2 is well quantized when trained at B>0 but not at B<0; the origin of this training asymmetry is unresolved, but may result from twist angle inhomogeneity.

— Incipient superconductivity and tunable Chern insulators in twisted Bernal bilayer-trilayer graphene  (2609.30202 - Waleffe et al., 24 Sep 2026) in Section “Chern insulators at integer and fractional fillings”