Over the past decades, the study of electronic behavior in novel materials has gained significant attention, driven by both the miniaturization of technology and the discovery of quantum effects at micro- and nanoscale dimensions. Meanwhile, there has also been significant progress in building graphene-based multilayer systems to engineer interesting band structures and boost correlation effects.

High-harmonic generation (HHG) are fundamentally interesting and frequently discussed as versatile probes of quantum materials with potential for optical information processing applications. Motivated by the successful demonstration of HHG in graphene, we here study this effect in rhombohedral stacks of n layers of graphene, a recent very prominent representative of correlated multilayer graphene systems.

We explore how the chiral Bloch states of the valleys of this system crucially affect the HHG, showing how the ‘winding’ of the Bloch states scales linearly with n, just like the dominant harmonic order. The presence of an interaction-induced splitting of the two valleys leads to a complex interplay between opposite chiralities of the two valleys, directly visible in the n dependence of the circular dichroism. We also analyze the impact of doping and identify a quantity that tracks the net chirality of the occupied states. Our findings show that rhombohedral graphene constitutes a promising platform for exploring rich nonlinear optical phenomena.