Condensed Matter Journal Club: "Sliding Ferroelectricity in 2D material: From atomic motion to artificial synapses"

Sliding ferroelectricity in van der Waals materials provides an atomically thin platform for integrating nonvolatile memory with programmable electronic transport. In rhombohedral (3R) MoS₂, individual monolayers lack out-of-plane polarization, but their stacking arrangement makes the two layers electronically inequivalent, producing asymmetric charge redistribution and a spontaneous out-of-plane dipole. A small lateral displacement interconverts two energetically equivalent stacking configurations with opposite polarization. An applied out-of-plane electric field favors one configuration, enabling polarization reversal through interlayer sliding and domain-wall propagation. Domain-wall pinning influences the switching threshold and stabilizes the programmed polarization after the electric field is removed. This coupling between atomic stacking and polarization provides a basis for nonvolatile memory and artificial synapses. In a ferroelectric semiconductor transistor, polarization modifies the channel electrostatic potential and carrier distribution, producing electrically distinguishable conductance states. Electrical pulses can program these states, with channel conductance representing the synaptic weight. Partial polarization switching offers a route to multilevel conductance and gradual weight updates analogous to synaptic potentiation and depression. We examine how switching kinetics and domain dynamics influence pulse-dependent conductance modulation, retention, and reproducibility, connecting the microscopic physics of sliding ferroelectricity to the requirements of neuromorphic devices.