Tuning the Electronic States of Bi2Se3 Films with Large Spin-Orbit Interaction Using Molecular Heterojunctions

TL;DR

This study demonstrates how molecular heterojunctions can tune the electronic states and enhance the spin-orbit interaction in Bi2Se3 thin films, with potential for optically controlled quantum transport applications.

Contribution

It introduces a method to modify spin-orbit coupling in topological insulator films using molecular diodes without destroying surface topology.

Findings

Charge transfer alters carrier density and mobility.

Spin-orbit lifetime decreases significantly with molecular diodes.

Optical irradiation can control the coupling effect.

Abstract

An electric bias can shift the Fermi level along the Dirac cone of a topological insulator and modify its charge transport, but tuning the electronic states and spin-orbit interaction (SOI) without destroying the surface topology is challenging. Here, we show that thin film Bi2Se3/n-p (p-n) molecular diodes form ordered interfaces where charge transfer and orbital re-hybridisation result in a decrease (increase) of the carrier density and improved mobility. In Bi2Se3 the spin-orbit lifetime, t_so, is 0.13 ps, which is comparable to the strongest spin-orbit materials. This lifetime drops further to 0.06 ps (0.09 ps) with the addition of p-n (n-p) molecular diodes, at the limit of measurable values. This strengthened spin-orbit interaction occurs even though molecules are made of light elements and increase the mean free path of the charge carriers by almost 50%, indicating changes to the Berry curvature and/or Rashba splitting around the hybridisation points. Raman spectroscopy gives evidence that the coupling effect may be controlled by optical irradiation, opening a pathway towards the design of heavy-light element hybrids with optically tunable quantum transport.