Tunable thermopower in a graphene-based topological insulator

TL;DR

This study demonstrates that graphene with randomly distributed indium or thallium adatoms can reliably exhibit a stable quantum spin Hall phase and high thermopower, with tunable temperature range and promising efficiency.

Contribution

It shows that a disordered adatom-decorated graphene system maintains a robust topological phase and exhibits tunable thermopower, simplifying experimental realization.

Findings

Stable quantum spin Hall phase despite disorder

Thermopower tunable from 1 to 80K with high efficiency

Homogeneous model effectively describes inhomogeneous system

Abstract

Following the recent proposal by Weeks et al., which suggested that indium (or thallium) adatoms deposited on the surface of graphene should turn the latter into a quantum spin Hall (QSH) insulator characterized by a sizeable gap, we perform a systematic study of the transport properties of this system as a function of the density of randomly distributed adatoms. While the samples are, by construction, very disordered, we find that they exhibit an extremely stable QSH phase with no signature of the spatial inhomogeneities of the adatom configuration. We find that a simple rescaling of the spin-orbit coupling parameter allows us to account for the behaviour of the inhomogeneous system using a homogeneous model. This robustness opens the route to a much easier experimental realization of this topological insulator. We additionally find this material to be a very promising candidate for thermopower generation with a target temperature tunable from 1 to 80K and an efficiency ZT close to 1.