Mapping the effect of defect-induced strain disorder on the Dirac states of topological insulators

TL;DR

This study investigates how defect-induced local strain affects the Dirac states in topological insulators, revealing nanoscale fluctuations in the Dirac spectrum caused by microscopic stain variations.

Contribution

It provides a microscopic understanding of how defect-induced strain influences Dirac states, extending beyond chemical potential fluctuation models.

Findings

Nanoscale fluctuations in Dirac point energy and velocity detected

Local stain couples to topological states, reshaping Dirac dispersion

Spatially varying stain impacts the electronic properties over large energy ranges

Abstract

We provide a detailed microscopic characterization of the influence of defects-induced disorder onto the Dirac spectrum of three dimensional topological insulators. By spatially resolved Landau-levels spectroscopy measurements, we reveal the existence of nanoscale fluctuations of both the Dirac point energy as well as of the Dirac-fermions velocity which is found to spatially change in opposite direction for electrons and holes, respectively. These results evidence a scenario which goes beyond the existing picture based on chemical potential fluctuations. The findings are consistently explained by considering the microscopic effects of local stain introduced by defects, which our model calculations show to effectively couple to topological states, reshaping their Dirac-like dispersion over a large energy range. In particular, our results indicate that the presence of microscopic spatially varying stain, inevitably present in crystals because of the random distribution of defects, effectively couple to topological states and should be carefully considered for correctly describing the effects of disorder.