Low energy rectified response of superconducting twisted bilayer graphene under the influence of disorder

Nonlinear responses hold important clues for underlying symmetries and hidden wavefunction-dependent details of a quantum material. Here, we reveal a novel rectified photocurrent in superconductors with a disorder-assisted 2Δ resonance at second order in electromagnetic field. In particular, we investigate the shift and injection currents in presence of disorder, and find large contributions from excitations between particle-hole quasiparticle bands which have been otherwise found to be vanishing even with complex pairing orders with intrinsically broken inversion symmetry. We demonstrate this in superconducting twisted bilayer graphene which due to its flat bands and enhanced quantum geometry is expected to host large responses. Such photocurrents could provide insights into symmetry properties and pairing mechanisms in superconductors with broader potential applications in microwave quantum sensing and next-gen optoelectronics.