Stacking and configuration dependent photocurrent in van der Waals heterostructures

Conventional photocurernts at p-n junctions depend on the macroscopic built-in field and are typically independent of microscopic details of atomic configurations. Here we demonstrate stacking and configuration dependent shift photocurrent in van der Waals heterostructures. Such shift current arises in noncentrosymmetric materials as a result of real-space shift of electrons upon photo-excitation and is thus sensitive to the symmetry and atomic arrangement in the unit cell. We illustrate the stacking and configuration dependence in Bernal stacked bilayers of graphene and graphene-like 2D materials. The shift photocurrent switches sign when the stacking arrangement is changed from AB to BA or the interlayer potential switches direction. The direction of the photocurrent depends on the light polarisation and is transverse when the polarisation is aligned with the high-symmetry axes of the material. Furthermore, in the presence of strain, the photocurrent is nonzero even for unpolarised light. Our results provide a tool to determine the stacking arrangement, lattice orientation and strain in van der Waals heterostructures from optical responses.