Optically probing the sliding ferroelectricity in 3R-MoS₂ bilayer

Under an external electric field, the out-of-plane polarization in the parallel-stacked transition metal dichalcogenides (TMDs) is shown to be switchable via an in-plane sliding motion [1]. Such a switchable spontaneous polarization together with a bandgap in the visible range makes the rhombohedral-stacked TMD a promising ferroelectric material for novel electronic and optoelectronic applications [2]. Besides the artificially stacked homobilayers, rhombohedral-stacking can also be realized in a chemically synthesized crystal of the 3R phase. In an exfoliated MoS₂ bilayer, the ferroelectric polarization is directly coupled to the excitonic effects through an asymmetric interlayer coupling [3]. Here, we present an optical method to probe the sliding ferroelectricity by utilizing such a direct coupling. Interestingly, we find that polarization switching can occur coherently over an area of more than 100 μm², unexpected for an exfoliated flake. Our work demonstrates the possibility of a non-volatile control of the optical response in rhombohedral-stacked TMDs.