Magnetic field Characterization of edge currents in quantum spin Hall insulators

TL;DR

This paper investigates the magnetic fields generated by edge currents in quantum spin Hall insulators and explores how nitrogen-vacancy centers can be used as local probes to detect spin accumulation and edge states.

Contribution

It provides a detailed calculation of magnetic fields near QSH edges and assesses NV centers as tools for characterizing topological insulator edge states.

Findings

Stronger magnetic fields are produced by larger band gaps and lower Fermi velocities.

Detectable spin accumulation is more concentrated near the edge with larger gaps.

Magnetic field detectability varies with the distance from the edge depending on the band gap.

Abstract

Quantum spin Hall (QSH) insulators are materials with nontrivial topological properties, characterized by helical edge currents. In 2D strips, the application of a bias voltage along the edge generates a magnetization that can be measured using quantum sensors and magnetometry techniques. In this work, we calculate the magnetic field in the vicinity of the edge and explore the potential role of nitrogen-vacancy (NV) centers in diamond as local probes for the characterization of QSH edge states in topological insulators. We characterize the magnetic field near the edges produced by both electron currents and spin accumulation at the edge. We focus on identifying the position from the edge at which the effects of spin accumulation become detectable. We observe that a larger gap between the conduction and valence bands, along with a lower Fermi velocity, results in a stronger magnetic field, with the detectable spin accumulation being more concentrated near the edge. Conversely, a smaller gap results in a slight reduction in the magnetic field magnitude, but the field associated with spin accumulation becomes detectable further from the edge. This work provides insights that could be useful for the characterization of topological materials and the development of novel electro-optical devices.