STM Spectroscopy of ultra-flat graphene on hexagonal boron nitride

TL;DR

This study uses STM to analyze ultra-flat graphene on hBN, revealing reduced charge fluctuations and conforming lattice structures, which enhances the potential for exploring Dirac physics in cleaner, more stable devices.

Contribution

It demonstrates that graphene on hBN exhibits significantly reduced charge disorder without opening a band gap, improving the platform for Dirac physics experiments.

Findings

Charge fluctuations are reduced by two orders of magnitude.

Graphene conforms to hBN without a sizable band gap.

Charge fluctuations are comparable to suspended graphene.

Abstract

Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy-momentum dispersion relations which cross at the Dirac point. However, accessing the physics of the low density region at the Dirac point has been difficult because of the presence of disorder which leaves the graphene with local microscopic electron and hole puddles, resulting in a finite density of carriers even at the charge neutrality point. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance. In this letter, we use scanning tunneling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moire patterns in the topographic images. However, contrary to recent predictions, this conformation does not lead to a sizable band gap due to the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron-hole charge fluctuations are reduced by two orders of magnitude as compared to those on silicon oxide. This leads to charge fluctuations which are as small as in suspended graphene, opening up Dirac point physics to more diverse experiments than are possible on freestanding devices.