Ambipolar transport in bulk crystals of a topological insulator by gating with ionic liquid

TL;DR

This study demonstrates that ionic-liquid gating can effectively control surface carrier types and induce ambipolar transport in bulk topological insulator crystals, enabling new experimental approaches.

Contribution

It introduces a method to achieve ambipolar transport in bulk topological insulators using ionic-liquid gating, with potential for reversible bulk doping.

Findings

Ionic-liquid gating controls surface carrier type in bulk crystals.

Achieved ambipolar transport in a bulk topological insulator.

Evidence of reversible electrochemical doping during gating.

Abstract

We report that the ionic-liquid gating of bulk single crystals of a topological insulator can control the type of the surface carriers and even results in ambipolar transport. This was made possible by the use of a highly bulk-insulating BiSbTeSe2 system where the chemical potential is located close to both the surface Dirac point and the middle of the bulk band gap. Thanks to the use of ionic liquid, the control of the surface chemical potential by gating was possible on the whole surface of a bulk three-dimensional sample, opening new experimental opportunities for topological insulators. In addition, our data suggest the existence of a nearly reversible electrochemical reaction that causes bulk carrier doping into the crystal during the ionic-liquid gating process.