High-harmonic generation in systems with chiral Bloch states: application to rhombohedral graphene

TL;DR

This paper investigates high-harmonic generation in rhombohedral graphene, revealing how chiral Bloch states influence nonlinear optical responses and offering insights into valley interactions and doping effects.

Contribution

It demonstrates the impact of chiral Bloch states on HHG in rhombohedral graphene and explores valley interactions, doping, and quantum geometry effects.

Findings

Winding of Bloch states scales linearly with the number of layers.

Strong quantum geometry imprints on momentum distribution at pulse start.

Valley splitting and chirality affect circular dichroism and doping response.

Abstract

Nonlinear light-matter interaction and, in particular, high-harmonic generation (HHG) are fundamentally interesting and frequently discussed as versatile probes of quantum materials with potential for optical information processing applications. Meanwhile, there has also been significant progress in graphene-based multilayer systems to engineer interesting band structures and boost correlation effects. 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 show how the chiral Bloch states of the valleys of this system crucially affect the HHG. The "winding" of the Bloch states scales linearly with $n$, just like the dominant harmonic order. The location of the strongest quantum geometry in momentum space on a ring of finite radius is shown to be imprinted on the time-dependent momentum distribution at the beginning of the strong laser pulse. We further demonstrate that the presence of an interaction-induced splitting of the two valleys leads to a complex interplay of the 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.