Chemical Potential Fluctuations in Topological Insulator (Bi$_{0.5}$Sb$_{0.5}$)$_2$Te$_3$ Films Visualized by Photocurrent Spectroscopy

TL;DR

This study visualizes chemical potential fluctuations in topological insulator films using photocurrent spectroscopy, revealing nanoscale disorder and thermoelectric effects at the interface, advancing understanding of surface state properties.

Contribution

The paper introduces a method to visualize and quantify chemical potential fluctuations in topological insulator films at the nanoscale using photocurrent spectroscopy.

Findings

Reproducible submicron photocurrent patterns linked to potential fluctuations

Potential disorder magnitude in the meV range quantified

Dominant photo-thermoelectric current observed in nanoscale constrictions

Abstract

We investigate the photocurrent properties of the topological insulator (Bi$_{0.5}$Sb$_{0.5}$)$_2$Te$_3$ on SrTiO$_3$-substrates. We find reproducible, submicron photocurrent patterns generated by long-range chemical potential fluctuations, occurring predominantly at the topological insulator/substrate interface. We fabricate nano-plowed constrictions which comprise single potential fluctuations. Hereby, we can quantify the magnitude of the disorder potential to be in the meV range. The results further suggest a dominating photo-thermoelectric current generated in the surface states in such nanoscale constrictions.