Tunable Layer Circular Photogalvanic Effect in Twisted Bilayers

TL;DR

This paper presents a comprehensive theory of the layer circular photogalvanic effect (LCPGE) in chiral bilayers, demonstrating its geometric origins and tunability in twisted bilayer graphene, with potential applications in frequency-sensitive light detection.

Contribution

It introduces a general geometric framework for LCPGE in bilayers and calculates its behavior in twisted bilayer graphene, revealing tunable resonance peaks across a broad frequency range.

Findings

LCPGE arises from interlayer coordinate shifts linked to quantum geometry.

Resonance peaks in LCPGE can be tuned from visible to infrared frequencies.

LCPGE enables potential infrared circularly polarized light detection.

Abstract

We develop a general theory of the layer circular photogalvanic effect (LCPGE) in quasi two-dimensional 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.