Second-Order Synaptic Memory using Inherent Plasticity of Moir\'e Superlattices

Achieving synaptic functionality electronically in a single-element quantum material is a fundamental challenge, as conventional methods rely on the introduction of extrinsic charge-traps or polar components. Here, we demonstrate that twisted double bilayer graphene (tDBLG) moir\'e superlattices, composed purely of carbon, exhibit electronic hysteresis and plasticity in presence of twist-angle disorder. Inversion symmetry breaking at the moir\'e length scales also gives rise to second-order nonlinear electrical response via disorder-mediated extrinsic mechanisms. Such second-order nonlinearity is highly tunable in both sign and magnitude by varying carrier concentration and vertical displacement field. We harness the coexistence of electronic plasticity and second-order nonlinearity to realize a second-order synaptic memory device. Our findings establish strained moir\'e carbon systems as a powerful new platform for energy-efficient neuromorphic computing, demonstrating that complex electronic functionality can emerge purely from symmetry breaking physics in a single-element material.