Single-layer behavior and slow carrier density dynamic of twisted graphene bilayer

TL;DR

This study uses STM and STS to investigate twisted graphene bilayer on SiC, revealing a unique defect-induced shift in the Dirac point linked to substrate decoupling and slow carrier density changes.

Contribution

It provides new insights into the local electronic behavior and slow carrier dynamics of twisted graphene bilayer on SiC substrates.

Findings

Dirac point located 0.40 eV below Fermi level at ~4.5° twist

Nanoscale defect causes Dirac point to shift towards Fermi level over 100 seconds

Decoupling from substrate reduces carrier density during measurements

Abstract

We report scanning tunneling microscopy (STM) and spectroscopy (STS) of twisted graphene bilayer on SiC substrate. For twist angle ~ 4.5o the Dirac point ED is located about 0.40 eV below the Fermi level EF due to the electron doping at the graphene/SiC interface. We observed an unexpected result that the local Dirac point around a nanoscaled defect shifts towards the Fermi energy during the STS measurements (with a time scale about 100 seconds). This behavior was attributed to the decoupling between the twisted graphene and the substrate during the measurements, which lowers the carrier density of graphene simultaneously.