Programmable SHG switching enabled by sliding ferroelectricity in bilayer MoS2

Achieving programmable second-harmonic generation (SHG) switching in two-dimensional materials is highly desirable for optical switching, communication, and information storage in next-generation integrated photonic technologies. In this work, we reveal that sliding ferroelectricity can programmably and reversibly modulate the SHG response, thereby enabling SHG switching in bilayer MoS2 based on compelling first-principles calculations. Interlayer sliding induces interfacial charge redistribution, giving rise to ferroelectric polarization reversal, accompanied by systematic modulation of interlayer coupling and electronic structure. Correspondingly, the SHG tensor is reconstructed in a symmetry-dependent manner, while the out-of-plane components exhibit a one-to-one correspondence with ferroelectric polarization reversal, realizing robust and programmable SHG switching with broad amplitude tunability. The underlying SHG polarity reversal originates from sign-inverted momentum-resolved susceptibility distributions and two-photon transitions between mirror-symmetric electronic states. The switching behavior is further manifested in polarization-resolved SHG patterns, which evolve from a threefold distribution to a sixfold pattern and recover with a rigid π/3 rotation. Building on these characteristics, we propose a sliding-ferroelectric nonlinear optical device enabling high-contrast optical readout in a compact footprint. Our work establishes sliding ferroelectricity as an effective paradigm for programmable SHG switching, shedding light on the intrinsic coupling of sliding ferroelectricity with SHG and guiding the design of ultrathin, integrated nonlinear photonic devices.