Tunable Layer Circular Photogalvanic Effect in Twisted Bilayers

Abstract

We develop a general theory of the layer circular photogalvanic effect (LCPGE) in quasi twodimensional chiral bilayers, which refers to the appearance of a polarization-dependent, out-of-plane dipole moment induced by circularly polarized light. We elucidate the geometric origin of the LCPGE as two types of interlayer coordinate shift weighted by the quantum metric tensor and the Berry curvature, respectively. As a concrete example, we calculate the LCPGE in twisted bilayer graphene, and find that it exhibits a resonance peak whose frequency can be tuned from visible to infrared as the twisting angle varies. The LCPGE thus provides a promising route towards frequency-sensitive, circularly-polarized light detection, particularly in the infrared range.

High-order nonlinear optical response of a twisted bilayer graphene

“…Another approach is the perturbation theory for the optical field. In this approach, the circular photogalvanic effect [70,71], one of the lowest-order nonlinear effects, has been found, but analyzing higher-order effects would become more challenging.…”

“…Indeed the interlayer coupling is important and, as shown in Fig. 4(c), there occurs significant charge transfer between the layers including some dc (0 ) component corresponding to the photogalvanic effect [70,71]. However, the in-plane currents accompanied by the interlayer hopping give less contribution to the total current.…”

Optical Coherent Injection of Carrier and Current in Twisted Bilayer graphene

“…This work mostly focuses on the comparison of the injection coefficients of twisted bilayer graphene and those of graphene, and there also exists other important injection processes appearing only in twisted bilayer graphene that are worth to be explored but not discussed here. For example, the stacking of two layers of graphene opens the responses along the perpendicular direction, 41 which are usually ignored in a monolayer graphene, the two-color optical injection tensors have nonzero components for oblique incident light. Moreover, due to the lower symmetry, a single color light with an appropriate polarization is also possible to inject currents.…”

Eshelby-twisted three-dimensional moiré superlattices

“…Chiral phenomena are an intensely studied topic in the field of condensed matter, such as chiral bands in Weyl semimetals [16], polarization of valley degrees of freedom [17], and chiral pairing in superconductivity [18]. Structural chirality will play a similar and important role as in the electronic chiral structures [19], giving rise to pseudomagnetic field [20] and nonreciprocal effects [21,22]. Eshelby twist can combine the features of 2D moiré superlattices and chirality in 3D to realize fantastic physics.…”