Evidence on the macroscopic length scale spin coherence for the edge currents in a narrow HgTe quantum well

TL;DR

This study provides experimental evidence of macroscopic-length-scale spin-coherent edge transport in a narrow HgTe quantum well, confirming the robustness and helical nature of edge currents in topological insulators.

Contribution

First experimental demonstration of macroscopic spin-coherent edge transport in a narrow HgTe quantum well with band inversion.

Findings

Edge current contribution is significant at zero magnetic field.

Transport is sensitive to the relative magnetization orientations of ferromagnetic contacts.

Spin coherence persists over distances of hundreds of micrometers.

Abstract

We experimentally investigate spin-polarized electron transport between two ferromagnetic contacts, placed at the edge of a two-dimensional electron system with band inversion. The system is realized in a narrow (8~nm) HgTe quantum well, the ferromagnetic side contacts are formed from a pre-magnetized permalloy film. In zero magnetic field, we find a significant edge current contribution to the transport between two ferromagnetic contacts. We experimentally demonstrate that this transport is sensitive to the mutual orientation of the magnetization directions of two 200~$\mu$m-spaced ferromagnetic leads. This is a direct experimental evidence on the spin-coherent edge transport over the macroscopic distances. Thus, the spin is extremely robust at the edge of a two-dimensional electron system with band inversion, confirming the helical spin-resolved nature of edge currents.