Twisting graphene to achieve programmable memory

Twisted double bilayer graphene (tDBLG) moiré superlattices have been shown to exhibit electronic hysteresis and plasticity due to twist-angle disorder. The inversion symmetry breaking at moiré length scales results in a second-order nonlinear electrical response through disorder-mediated extrinsic mechanisms. By controlling carrier concentration and vertical displacement field, the sign and magnitude of this nonlinearity are tunable. These combined effects allow the realization of a second-order synaptic memory device, showing that complex functions can arise from symmetry-breaking physics in single-element materials.