Fig. 1: Dual polarization in transition metal dichalcogenides/black phosphorus (TMD/BP) heterostructure.
From: Dual polarization-enabled ultrafast bulk photovoltaic response in van der Waals heterostructures
a Symmetry breaking in TMD monolayers. Five polar groups can be obtained by breaking the D3h symmetry for the bulk photovoltaic effect (BPVE). b Polar symmetry Cs obtained by stacking a TMD monolayer onto a BP monolayer. The generated in-plane and out-of-plane polarizations are illustrated by the white and the yellow arrows, respectively. The green and red arrows indicate the charge carrier transfer in conductive band (CB) and valance band (VB), respectively.
