Quasi-two-dimensional spin helix and magnon-induced singularity in twisted bilayer graphene

TL;DR

This paper explores the emergence of a quasi-two-dimensional spin helix and magnon-induced singularity in twisted bilayer graphene, revealing complex correlated phenomena involving Kondo physics, Luttinger liquids, and magnetism.

Contribution

It introduces a novel coupled system of localized spins and interacting electrons in twisted bilayer graphene, predicting a spin helix phase and magnon-induced singularities with experimental signatures.

Findings

Prediction of a spin helix phase in twisted bilayer graphene.

Identification of magnon-induced singularities affecting correlation functions.

Observable magnetic resonance and susceptibility features as experimental indicators.

Abstract

Twisted bilayer graphene exhibits prominent correlated phenomena in two distinct regimes: a Kondo lattice near the magic angle, resembling heavy fermion systems, and a triangular correlated domain wall network under interlayer bias, akin to sliding Luttinger liquids previously introduced for cuprates. Combining these characteristics, here we investigate a system where interacting electrons in the domain wall network couple to localized spins. Owing to inter-domain-wall correlations, a quasi-two-dimensional spin helix phase within the localized spins emerges as a result of spatial phase coherence across parallel domain walls. Within the spin helix phase, magnons can induce a singularity, reflected in the scaling exponents of various correlation functions, accessible through electrical means and by adjusting the twist angle. We predict observable features in magnetic resonance and anisotropic paramagnetic spin susceptibility for the spin helix and the magnon-induced singularity, serving as experimental indicators of the interplay between the Kondo lattice and sliding Luttinger liquids. Integrating critical aspects of Luttinger liquid physics, magnetism, and Kondo physics in twisted bilayer graphene, our findings offer insights into similar correlated phenomena across a broad range of twisted van der Waals structures.