Global and Local Optoelectronic Probes of Out-of-Equilibrium Criticalities in Tunable Graphene Moiré Superlattices

2D moiré crystals have opened a new era in quantum materials, offering a tunable platform to engineer novel electronic properties. Thanks to their narrow bands, they provide a unique system to explore the nonlinear and out-of-equilibrium physics of electrons under high electric fields. As the DC bias current increases, graphene superlattices show a drastic change in transport properties, marked by a peak in differential resistivity at a critical current [1]. This out-of-equilibrium criticality is believed to mark a transition from a Fermi-liquid to an electron–hole plasma, and has proven extreme sensitivity to light, enabling broadband single-photon detection [2]. Yet, the microscopic nature of this transition and its interaction with light is still unknown. We investigate this regime in Bernal bilayer graphene aligned to hBN, whose bandstructure can be modified with external electric fields. By measuring changes in the critical current, we demonstrate the sensitivity of nonlinear transport to variations in moiré bands and its ability to probe their bandwidth. Using scanning photocurrent microscopy, we reveal field-induced domains hosting the observed nonlinearities and provide new insight into the origin of the criticality. Our results establish the high-bias regime as a new probe of moiré minibands and as a platform to exploit the physics of nonequilibrium electrons for novel optoelectronic applications.  

 

[1] - Berdyugin A. I. et al. Science 375, (2022).

[2]- Nowakowski K. et al. Science 389, (2025).