Spin Susceptibility and Helical Magnetic Orders at the Edges/Surfaces of Topological Insulators Due to Fermi Surface Nesting

TL;DR

This paper investigates how Fermi surface nesting induces helical spin density waves and magnetic orders on the edges and surfaces of topological insulators, highlighting the role of spin-momentum locking and time-reversal symmetry.

Contribution

It reveals that Fermi surface nesting leads to helical spin susceptibility and magnetic orders, a novel insight into magnetic phenomena in topological insulators.

Findings

Helical spin density wave state emerges at low temperature due to nesting.

Spin susceptibility exhibits strong helical features at the nesting wavevector.

Predicted helical magnetic order in magnetically doped topological insulator surfaces.

Abstract

We study spin susceptibility and magnetic order at the edges/surfaces of two-dimensional and three-dimensional topological insulators when the Fermi surface is nested. We find that due to spin-momentum locking as well as time-reversal symmetry, spin susceptibility at the nesting wavevector has a strong {\em helical} feature. It follows then, a {\em helical} spin density wave (SDW) state emerges at low temperature due to Fermi surface nesting. The helical feature of spin susceptibility also has profound impact on the magnetic order in magnetically doped surface of three dimensional topological insulators. In such system, from the mean field Zener theory, we predict a {\em helical} magnetic order.