Giant Nonlinear Optical Response via Coherent Stacking of In-Plane Ferroelectric Layers

Thin ferroelectric materials hold great promise for compact nonvolatile memory and nonlinear optical and optoelectronic devices. Herein, an ultrathin in-plane ferroelectric material that exhibits a giant nonlinear optical effect, group-IV monochalcogenide SnSe, is reported. Nanometer-scale ferroelectric domains with approximate to 90 degrees/270 degrees twin boundaries or approximate to 180 degrees domain walls are revealed in physical-vapor-deposited SnSe by lateral piezoresponse force microscopy. Atomic structure characterization reveals both parallel and antiparallel stacking of neighboring van der Waals ferroelectric layers, leading to ferroelectric or antiferroelectric ordering. Ferroelectric domains exhibit giant nonlinear optical activity due to coherent enhancement of second-harmonic fields and the as-resulted second-harmonic generation was observed to be 100 times more intense than monolayer WS2. This work demonstrates in-plane ferroelectric ordering and giant nonlinear optical activity in SnSe, which paves the way for applications in on-chip nonlinear optical components and nonvolatile memory devices.

Automated summary

Thin ferroelectric material SnSe with nanometer-scale ferroelectric domains exhibiting giant nonlinear optical effect and coherent enhancement of second-harmonic fields was reported. The ferroelectric domains show 90 degrees/270 degrees twin boundaries or 180 degrees domain walls and have parallel and antiparallel stacking of neighboring van der Waals ferroelectric layers. The second-harmonic generation in SnSe was observed to be 100 times more intense than monolayer WS2, demonstrating its potential in on-chip nonlinear optical components and nonvolatile memory devices.