Layer-independent and layer-dependent nonlinear optical properties of two-dimensional GaX (X = S, Se, Te) nanosheets

This is the authors' abstract. We don't add key points for this paper.

-GaSe crystals are very close to that of the GaSe ML, showing no dependence on the layer number. The magnitude of the SHG coefficient of the trilayer exfoliated from the bulk β-GaSe crystals is around 1/3 of that of the GaSe ML, decreasing rapidly with the layer number. This study indicates that a strong SHG response can be obtained in a wide range of monolayers and few-layers. Moreover, we point out that one can identify the layer number and the stacking sequence of 2D nanosheets by measuring their elastic constants and SHG coefficients.