Band manipulation and spin texture in interacting moir\'e helical edges

TL;DR

This paper presents a theoretical framework for controlling the band structure and spin texture of interacting helical edge states in topological insulators using moiré potentials, enabling gap suppression and flat band creation.

Contribution

It introduces a novel method to manipulate the edge band structure and spin texture via external moiré potentials, including gap suppression and Dirac point re-emergence.

Findings

Interacting edge band gaps can be tuned and suppressed by moiré potentials.

Moiré potentials can create nearly flat bands with long periods.

The approach enhances coherence length of helical edges by gap suppression.

Abstract

We develop a theory for manipulating the effective band structure of interacting helical edge states realized on the boundary of two-dimensional time-reversal symmetric topological insulators. For sufficiently strong interaction, an interacting edge band gap develops, spontaneously breaking time-reversal symmetry on the edge. The resulting spin texture, as well as the energy of the the time-reversal breaking gaps, can be tuned by an external moir\'e potential (i.e., a superlattice potential). Remarkably, we establish that by tuning the strength and period of the potential, the interacting gaps can be fully suppressed and interacting Dirac points re-emerge. In addition, nearly flat bands can be created by the moir\'e potential with a sufficiently long period. Our theory provides an unprecedented way to enhance the coherence length of interacting helical edges by suppressing the interacting gap. The implications of this finding for ongoing experiments on helical edge states is discussed.