Giant nonlinear Hall effect in isospin symmetry broken bilayer graphene.

Spontaneous isospin ordering fundamentally reshapes quantum nonlinear transport, yet the nature of nonlinear responses in strongly correlated and symmetry-broken quantum states remain largely unexplored. In this work, we investigate a regime where symmetry breaking is not static but emerges dynamically as a tunable property of the electronic system, driven by strong correlations. Using high-quality, dual-gated Bernal bilayer graphene, we observe a giant nonlinear Hall conductivity (9.1 µm S V⁻¹) that manifests strongly in a field-driven isospin-polarized phase. In this correlated regime, the nonlinear conductivity scales exponentially with the linear conductivity, in stark contrast to the quadratic scaling expected in conventional nonlinear systems. Combined with quantum oscillation measurements and self-consistent theoretical modelling, our results indicate that this giant response is closely linked to an interaction-driven valley-polarized state. Our findings establish spontaneous isospin symmetry breaking as an effective route to giant nonlinear quantum transport, where interaction-enhanced skew scattering emerges as the dominant transport mechanism.