Electronic transport properties and quantum localization effects monitored by selective functionalization in Bernal bilayer graphene

TL;DR

This study investigates how selective functionalization affects the electronic transport and localization in Bernal bilayer graphene, revealing complex behaviors like gap opening and abnormal conductivity influenced by adsorbate placement and concentration.

Contribution

It provides a detailed numerical analysis of the combined effects of multiple adsorbate types and their positions on BLG's electronic properties, highlighting quantum effects often neglected in semi-classical models.

Findings

Quantum effects significantly influence electronic structure at low doping.

Adsorbate position and concentration determine gap opening and conductivity.

Midgap states enable conduction via quantum fluctuations despite zero average velocity.

Abstract

Monitoring electronic properties of 2D materials is an essential step to open a way for applications such as electronic devices and sensors. From this perspective, Bernal bilayer graphene (BLG) is a fairly simple system that offers great possibilities for tuning electronic gap and charge carriers' mobility by selective functionalization (adsorptions of atoms or molecules). Here, we present a detailed numerical study of BLG electronic properties when two types of adsorption site are present simultaneously. We focus on realistic cases that could be realized experimentally with adsorbate concentration c varying from 0.25% to 5%. For a given value of c, when the electronic doping is lower than c we show that quantum effects, which are ignored in usual semi-classical calculations, strongly affect the electronic structure and the transport properties. A wide range of behaviors is indeed found, such as gap opening, metallic behavior or abnormal conductivity, which depend on the adsorbate positions, the c value, the doping, and eventually the coupling between midgap states which can create a midgap band. These behaviors are understood by simple arguments based on the fact that BLG lattice is bipartite. We also analyze the conductivity at low temperature, where multiple scattering effects cannot be ignored. Moreover, when the Fermi energy lies in the band of midgap states, the average velocity of charge carriers cancels but conduction is still possible thanks to quantum fluctuations of the velocity.