Imaging the topological current carrying state and the surface to bulk transformation, in Bi2Se3 single crystal and thin film

TL;DR

This study uses magneto-optics to image topological surface currents in Bi2Se3, revealing temperature-driven surface-to-bulk transformation and edge current behavior in thin films, highlighting disorder-driven phase transition phenomena.

Contribution

It provides direct imaging of topological current distribution and surface-bulk transformation in Bi2Se3, demonstrating the temperature dependence and magnetic field effects on edge currents.

Findings

Surface current sheets are about 3.6 nm thick at low temperatures.

Temperature induces a transition from surface to bulk current, resembling a classical phase transition.

Weak magnetic fields suppress edge currents, leading to uniform bulk currents.

Abstract

Magneto-optics based current imaging technique compares the nature of topological current distribution in a single crystal and thin film of topological insulator material, Bi2Se3. The single crystal, at low temperatures, has uniform topological surface current sheets which are about 3.6 nm thick. With increasing temperature, the current partially diverts into the crystal bulk and concomitantly, the sheet break up into a patchy network of high and low current density regions. The temperature dependence of the high current density areas shows that the surface to bulk transformation in the crystal has features of classical phase transition phenomena. The surface area fraction with topological high current density behaves like an order parameter. This phase transition is driven by disorder. In Bi2Se3 thin film we show the presence of quasi one-dimensional topological edge currents which are suppressed with a weak applied magnetic field. The edge current transforms into a uniform bulk current in the film.