Julien Barrier
The response of a metallic system to an electric field is usually described by a displacement of the Fermi surface in momentum space. For low fields, the displacement is small enough that the drift velocity is small compared to the Fermi velocity. In such linear regime, the voltage across a sample scales linearly with the sourced current.
Moiré superlattices, created stacking together two-dimensional materials with small alignment mismatch between their crystallographic axes, produce smooth periodic potentials with a reduced Fermi velocity and small bandwidth, which enable large Fermi surface displacements. The superlattice can be driven into a supercritical regime where extra-carriers are produced through inter-band transitions. I will show that this effect is generic to all known moiré materials, with a critical behaviour that can be leveraged to map the bandwidth of moiré superlattices. Deep into the non-linear regime, a region of negative differential conductivity with a bistable state emerges with giant photo-response. Operating in this regime, I will demonstrate single photon detection at mid-IR and visible wavelengths.