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Stacking atomically thin two-dimensional materials with a rotational misalignment between their layers produces a van der Waals bilayer in which all mirror symmetries can be broken. A fundamental experimental signature of a twisted multilayer is circular dichroism (CD): the conversion of a linearly polarized incident optical field to an elliptically polarized field in transmission. This work investigates the relations between CD, the twist angle, and interlayer slip. In experiments where bilayers are formed by contacting one layer with another, the relative rotation angle between the symmetry axes of each sheet are controlled, but the lateral shifts between the layers are not. Accounting for the lateral shift between the layers expands the configuration space of twisted bilayer structures. Here we demonstrate how the symmetry constraints in this expanded configuration space are expressed in the CD spectrum of twisted bilayer graphene as a function of the rotation angle and interlayer slip.
Addison et al. (Fri,) studied this question.