Nanoscale view of engineered massive Dirac quasiparticles in lithographic superstructures

TL;DR

This study demonstrates a novel method to engineer and visualize massive Dirac quasiparticles in graphene superstructures at the nanoscale, revealing tunable band gaps and effective masses through lithography and spectroscopy.

Contribution

It introduces a new approach for band structure engineering by lithographically patterning graphene to induce and directly observe massive Dirac fermions with tunable properties.

Findings

Linear scaling of effective mass with feature size

Electrostatic doping enhances effective hole mass

Observation of a 0.64 eV band gap in superstructures

Abstract

Massive Dirac fermions are low-energy electronic excitations characterized by a hyperbolic band dispersion. They play a central role in several emerging physical phenomena such as topological phase transitions, anomalous Hall effects and superconductivity. This work demonstrates that massive Dirac fermions can be controllably induced by lithographically patterning superstructures of nanoscale holes in a graphene device. Their band dispersion is systematically visualized using angle-resolved photoemission spectroscopy with nanoscale spatial resolution. A linear scaling of effective mass with feature sizes is discovered, underlining the Dirac nature of the superstructures. In situ electrostatic doping dramatically enhances the effective hole mass and leads to the direct observation of an electronic band gap that results in a peak-to-peak band separation of (0.64 $\pm$ 0.03) eV, which is shown via first-principles calculations to be strongly renormalized by carrier-induced screening. The presented methodology outlines a new approach for band structure engineering guided by directly viewing structurally- and electrically-tunable massive Dirac quasiparticles in lithographic superstructures at the nanoscale.