Velocity and confinement of edge plasmons in HgTe-based 2D topological insulators

TL;DR

This study measures the plasmon velocity in HgTe-based 2D topological insulators, revealing the significant impact of charge puddles on edge state transport and highlighting challenges for robust topological conduction.

Contribution

It provides the first phase-resolved GHz measurement of edge plasmon velocity in HgTe quantum wells in QSH and QH regimes, emphasizing the role of charge puddles.

Findings

Low plasmon velocities observed, indicating large transverse widths.

Charge puddles significantly influence edge plasmon behavior.

Puddles may hinder the development of robust edge transport.

Abstract

High-frequency transport in the edge states of the quantum spin Hall (QSH) effect has to date rarely been explored, though it could cast light on the scattering mechanisms taking place therein. We here report on the measurement of the plasmon velocity in topological HgTe quantum wells both in the QSH and quantum Hall (QH) regimes, using harmonic GHz excitations and phase-resolved detection. We observe low plasmon velocities corresponding to large transverse widths, which we ascribe to the prominent influence of charge puddles forming in the vicinity of edge channels. Together with other recent works, it suggests that puddles play an essential role in the edge state physics and probably constitute a main hurdle on the way to clean and robust edge transport.