Moire folded helical states at the interfaces of heterostructures

TL;DR

This paper models moire superlattices in graphene heterostructures, showing how spin orbit interactions reshape minibands, induce helicity fragmentation, and support relativistic quasiparticles, revealing new ways to engineer spin-related properties.

Contribution

It introduces a minimal model demonstrating how moire patterns amplify spin orbit effects and generate complex miniband structures with emergent helicity and Dirac crossings.

Findings

Moire patterns modulate Rashba spin orbit interaction.

Spin orbit lifts degeneracy and reduces spectral periodicity.

Helicity fragmentation enhances helicity fluctuations.

Abstract

A minimal model of a graphene topological insulator heterostructure is considered, where a moire superlattice modulates the Rashba spin orbit interaction. In the spin degenerate, spin orbit free limit, the reduced Brillouin zone contains flat, spin degenerate moire minibands, with periodicity determined by superlattice folding. The inclusion of spin orbit interaction lifts the spin degeneracy and reduces the effective spectral periodicity by a factor of two. Through spin orbit interaction, the moire potential entangles spin, sublattice, and leg degrees of freedom, reshaping the miniband structure in momentum space and generating emergent helicity spectral functions. As the Rashba coupling is renormalized by the moire pattern, it induces helicity fragmentation, in which the helicity weight is distributed across a dense manifold of moire minibands, forming an extended network of helicity carrying states and significantly enhancing helicity fluctuations at the bare response level. The emergence of Dirac like miniband crossings at finite spin orbit interaction demonstrates that moire heterostructures can support relativistic quasiparticles through band reconstruction. This model provides a microscopic mechanism by which proximity induced spin orbit coupling can be amplified via moire engineering.